Optical detector, methods of forming and operating the same

Abstract

Various embodiments may relate to an optical detector including a first photosensitive element including a two-dimensional material. The optical detector may also include a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The optical detector may further include a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element. An armchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.

Description

OPTICAL DETECTOR, METHODS OF FORMING AND OPERATING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No. 10202302985X filed October 23, 2023, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] Various embodiments of this disclosure may relate to an optical detector. Various embodiments of this disclosure may relate to a method of forming an optical detector. Various embodiments of this disclosure may relate to a method of operating an optical detector.BACKGROUND

[0003] The inherent properties of a light field, such as polarization, intensity and wavelength, provide multidimensional optical information for numerous applications including, but not limited to, environmental monitoring, thermal imaging, medical diagnosis and free-space communications. Simultaneous detection of this multidimensional optical information provides many degrees of freedom for accurately identifying diverse targets and performing multiform tasks in parallel in complex environments. Currently, most of the previously reported photodetectors can only detect information in one dimension, either wavelength, intensity or polarization, due to the intercoupling of various polarization states with light intensity and wavelength which makes detection in multiple dimensions more challenging. In addition, the actual polarization state cannot be accurately detected by most available photodetectors because the photocurrents measured at different polarization angles (0) overlap twice (have the same values) in the range from 0° to 180° such that the angles 0 and (180° - 0) cannot be differentiated.

[0004] Recently, a few attempts have been made to create photodetectors using two- dimensional (2D) materials and artificial metasurfaces to detect multidimensional optical information through their tailorable device architectures and physical properties For example, a twisted double-bilayer graphene photodetector is capable of determining polarization, wavelength and intensity due to its gate-tunable moire quantum geometry, but thisimplementation requires a complex convolutional neural network trained with big data. In addition, various polarization states can be precisely identified using twisted black phosphorus polarimeters, 2D black arsenic phosphorus (b-AsP)Ztungsten sulfide (WS2) / b-AsP van der Waals heterostructures and 2D material / metasurface hybrid structures However, extraction of light intensity from these devices still requires an additional power-calibrated device to decouple the intensity-polarization relationship, which results in an increase in system complexity and device size. Moreover, it is even more difficult for those devices to obtain wavelength information that is coupled with the polarization angles. It therefore remains a challenge to simultaneously and unambiguously acquire multidimensional optical information using a compact and miniaturized device.SUMMARY

[0005] Various embodiments may relate to an optical detector. The optical detector may include a first photosensitive element including a two-dimensional material. The optical detector may also include a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The optical detector may further include a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element. An armchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.

[0006] Various embodiments may relate to a method of forming an optical detector. The method may include forming a first photosensitive element including a two-dimensional material. The method may also include forming a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The method may additionally include fonning a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element. An annchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a seconddirection different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.

[0007] Various embodiments may relate to a method of operating an optical detector. The method may include providing a light to the optical detector. The optical detector may include a first photosensitive element include a two-dimensional material. The optical detector may also include a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The optical detector may further include a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element. The method may also include determining a first photocurrent flowing through the first homojunction. The method may additionally include determining a second photocurrent flowing through the second homojunction. An armchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.FIG. 1 provides a general illustration of the optical detector including the features according to various embodiments.FIG. 2 provides a schematic of one possible implementation of the optical detector according to various embodiments.FIG. 3 shows a general illustration of a method of forming an optical detector according to various embodiments.FIG. 4 shows a general illustration of a method of operating an optical detector according to various embodiments.FIG. 5A shows a schematic of an optical detector according to various embodiments.FIG. 5B shows (above) a perspective view and (below) a top view illustrating the anisotropic structure of black arsenic phosphorus (b-AsP) according to various embodiments.FIG. 5C shows schematics illustrating the predicted photocurrent signs in the optical detector according to various embodiments under illumination with different polarization angles.FIG. 5D shows plots of absorption / temperature and hole concentrations illustrating the absorption, temperature and hole concentration profiles of the various flakes of the optical detector according to various embodiments under illumination of light at polarization angles 0 = 0° and 90°.FIG. 5E shows a two-dimensional plot of predicted first photocurrent IDS, J) as a function of predicted second photocurrent IDS, 2) of the optical detector according to various embodiments at different polarization angles (0) and incident intensities (P), which enables simultaneous detection of 0 and P.FIG. 6A shows an optical microscopy image of an optical detector (device 1) according to various embodiments.FIG. 6B shows an atomic force microscopy (AFM) image illustrating the topology of the optical detector (device 1) according to various embodiments. The thickness of these b-AsP flakes was determined to be ~ 120 nm.FIG. 6C shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the left black arsenic phosphorus (L-AsP) flake of the optical detector (device 1) according to various embodiments.FIG. 6D shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the middle black arsenic phosphorus (M-AsP) flake of the optical detector (device 1) according to various embodiments.FIG. 6E shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the right black arsenic phosphorus (R-AsP) flake of the optical detector (device 1) according to various embodiments.FIG. 6F shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 1) according to various embodiments, which makes it possible to determine the crystal orientation of the b-AsP flake via Ag2 / Ag1(armchair or AC) > Ag2 / Ag1(zig-zag or ZZ).FIG. 6G shows the anisotropic optical absorption of a black arsenic phosphorous (b-AsP) flake (-126 nm thick) according to various embodiments at a wavelength 1 = 3.7 pm.FIG. 7A shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of a black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of - 55 nm for polarization angles from 0° to 90°, with the inset showing a microscopy optical image of the b-AsP flake.FIG. 7B shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 7A according to various embodiments for polarization angles from 100° to 180°.FIG. 7C shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG 7A according to various embodiments for polarization angles from 190° to 270°.FIG. 7D shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 7A according to various embodiments for polarization angles from 280° to 350°.FIG. 7E shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b- AsP) flake according to various embodiments with a thickness of - 55 nm for polarization angles from 0° to 90°.FIG. 7F shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b- AsP) flake according to various embodiments for polarization angles from 100° to 180°.FIG. 7G shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenicphosphorous (b-AsP) flake according to various embodiments for polarization angles from 190° to 270°.FIG. 7H shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 280° to 350°.FIG. 71 shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of - 55 nm for polarization angles from 0° to 90°.FIG. 7J shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 100° to 180°.FIG. 7K shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 190° to 270°.FIG. 7L shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 280° to 350°.FIG. 7M shows the anisotropic optical absorption of a black arsenic phosphorous (b-AsP) flake (-55 nm thick) according to various embodiments at a wavelength = 3.7 pm.FIG. 7N shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the optical absorption in the armchair (AC) orientation of black arsenic phosphorous (b-AsP) flakes with different thicknesses according to various embodiments.FIG. 70 shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of- 126 nm forpolarization angles from 0° to 90°, with the inset showing a microscopy optical image of the b-AsP flake.FIG. 7P shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 70 according to various embodiments for polarization angles from 105° to 165°.FIG. 8A shows a plot of the first photocurrent IDS.I (in micro-Amperes or pA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. FIG. 8B shows a plot of the second photocurrent IDS.2 (in micro-Amperes or pA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. 0° and 90° refer to the polarization angles of the incident light.FIG. 8C shows a plot of the first photocurrent IDS.I (in micro-Amperes or pA) as a function of drain-source voltage VDS (in volts or V) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments under large VDS bias voltage range (±1V) in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2.FIG. 8D shows a plot of the second photocurrent IDS.2 (in micro-Amperes or pA) as a function of drain-source voltage VDS (in volts or V) illustrating the IDS - VDS characteri sties of the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments under large VDS bias voltage range (±1V) in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2.FIG. 8E shows a plot of the first photocurrent IDS.I (in micro-Amperes or pA) as a function of gate-source voltage VGS (in volts or V) illustrating the transfer characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments under dark and a drain-source voltage VDS of 10 mV.FIG. 8F shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) as a function of gate-source voltage VGS (in volts or V) illustrating the transfer characteristics of the secondhomojunction (HJ-2) of the optical detector (device 1) according to various embodiments under dark and a drain-source voltage VDS of 10 mV.FIG. 9A shows a schematic of the photocurrent mapping measured from the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments.FIG. 9B shows the simplified diagram of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments.FIG. 9C shows the qualitative band diagram of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments.FIG. 9D shows a schematic diagram of carrier flow dominated by photovoltaic (PV) effect according to various embodiments. The photocurrent signs at positions 1 - 4 are marked asFIG. 9E shows a schematic diagram of carrier flow dominated by the photothermoelectric (PTE) effect according to various embodiments.FIG. 10A shows a plot of photocurrents IDS,I IDS, 2 (in micro- Amperes or pA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments when the polarization angle 6 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity ( / ■’) of 28.7 W cm-2.FIG. 10B shows a plot of the first photocurrent IDS,I (in micro-Amperes or pA) exhibited by the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of polarization angle 9 (in degrees or deg) under 3.7 pm laser illumination at different incident intensities (1.9, 6.7, 11.4, 18.1, 23.9 and 28.7 W cm l.FIG. 10C shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) exhibited by the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or deg) under 3.7 pm laser illumination at different incident intensities (1.9, 6.7, 11.4, 18.1, 23.9 and 28.7 W cm-2). These photocurrents were measured at VDS = 0V.FIG. 10D shows a plot of the first photocurrent IDS,I (in nano- Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 6 (in degrees or °) under 3.7 pm laser illumination at different low incident intensities (0.05. 0.1, 0.3 and 0.5 W cm-2).FIG. 10E shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 6 (in degrees or °) under 3.7 pm laser illumination at different low incident intensities (0.05. 0.1, 0.3 and 0.5 W cm"2).FIG. 10F shows a plot of the first photocurrent IDS,I (in micro- Amperes or A) exhibited by the optical detector (device 1) according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrents of the optical detector (device 1) according to various embodiments with incident intensity under 3.7 pm laser illumination at two selected polarization angles 0 = 20° and 110°.FIG. 10G shows a plot of the second photocurrent IDS, 2 (in micro- Amperes or A) exhibited by the optical detector according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrents of the optical detector (device 1) according to various embodiments with incident intensity under 3.7 pm laser illumination at two selected polarization angles 0 = 70° and 160°.FIG. 10H shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 3.7 pm laser illumination for different intensities and polarization angles such that the polarization angle from 0° to 180° and incident intensity from 0.05 W / cm2to 0.5 W / cm2can be simultaneously determined.FIG. 101 shows a two dimensional plot of the first photocurrent IDS.I (in micro- Amperes or pA) as a function of the second photocurrent IDS, 2 (in micro- Amperes or pA) of the optical detector (device 1) according to various embodiments under 3.7 pm laser illumination for different intensities and polarization angles such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determined.FIG. 1 1 A shows a plot of the photocurrent IDS (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments to different wavelengths with a polarization angle of 0° at drain-source bias VDS = 0 V.FIG. 1 IB shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of the power density (in Watts per square centimeter or W cm'2) illustrating thevariation of photocurrent with power density at different wavelengths with polarization angle 6 = 0°, showing a linear dependence on intensity (IDS ~ P').FIG. 11C shows a plot of photocurrent IDS (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) according to various embodiments for 3.7 gm laser illumination.FIG. 1 ID shows a plot of photocurrent IDS (in micro- Amperes or gA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments for 3.7 gm laser illumination.FIG. 1 IE shows a plot of photocurrent IDS (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) according to various embodiments for 4.6 gm laser illumination.FIG. 1 IF shows a plot of photocurrent IDS (in micro-Amperes or gA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments for 4.6 gm laser illumination.FIG. 1 1 G shows a plot of photocurrent IDS (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) according to various embodiments for 5.7 gm laser illumination.FIG. 11H shows a plot of photocurrent IDS (in micro-Amperes or gA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments for 5.7 gm laser.FIG. 12A shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths.FIG. 12B shows a plot of responsivity (in milli- Amperes per Watt or mA / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation responsivity of the optical detector (device 1 ) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.FIG. 12C shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of wavelength (in micro-meters or gm) illustrating the wavelength-dependent responsivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1)according to various embodiments for polarization angle 9 = 0° and drain-source bias VDS = 0V.FIG. 12D shows a plot of noise current (in square Amperes per Hertz or A2 / Hz) as a function of frequency (in Hertz or Hz) illustrating variation of noise currents of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with frequency.FIG. 12E shows a plot of noise equivalent power NEP (in pico-Watts per square-root Hertz or pW / Hz°5) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the NEP of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.FIG. 12F shows a plot of detectivity (x lO9centimeter square-root Hertz per Watt or cm Hz05 / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the detectivity of the first homojunction HJ-1 and the second homojunction HJ- 2 of the optical detector (device 1) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.FIG. 12G shows a plot of detectivity (* 109cm centimeter square-root Hertz per Watt or cm Hz05 / W) as a function of wavelength (in micrometer or pm) illustrating the wavelengthdependent detectivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1 ) according to various embodiments for polarization angle 9 = 0° and drain-source bias VDS = 0V.FIG. 13 A shows a plot of normalized voltage (in arbitrary units or a.u.) as a function of time (in milli-seconds or ms) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments.FIG. 13B shows a plot of normalized voltage (in arbitrary units or a.u.) as a function of time (in milli-seconds or ms) illustrating the response time with a rising time of ~21 ps and a decay time of ~17 ps of the optical detector (device 1) according to various embodiments.FIG. 14A shows a plot of the first photocurrent IDS.I (in nano- Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 4.6 pm laser illumination at different incident intensities from 0.2 W / cm2to 16.7 W / cm2.FIG. 14B shows a plot of the second photocurrent IDS.2 (in nano- Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 4.6 pm laser illumination at different incident intensities from 0.2 W / cm2to 16.7 W / cm2.FIG. 14C shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 4.6 pm laser illumination for different intensities from 2.0 W / cm2to 16.7 W / cm2and polarization angles 0° to 180°.FIG. 14D shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 4 6 pm laser illumination for different intensities of 0.2 W / cm2and 0.9 W / cm2and polarization angles 0° to 180°.FIG. 14E shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with incident intensity under 4.6 pm laser illumination at two selected polarization angles 0 = 20°and 110°.FIG. 14F shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity under 4.6 pm laser illumination at two selected polarization angles 0 = 70°and 160°.FIG. 15A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities from 0.6 W / cm2to 34.1 W / cm2.FIG. 15B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities from 0.6 W / cm2to 34.1 W / cm2,FIG. 15C shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector(device 1) according to various embodiments under 5.7 gm laser illumination for different intensities from 6.9 W / cm2to 34.1 W / cm2and polarization angles 0° to 180°.FIG. 15D shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 5.7 pm laser illumination for different intensities of 0.6 W / cm2, 1.5 W / cm2, and 2.8 W / cm2and polarization angles 0° to 180°.FIG. 15E shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the optical detector according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with incident intensity under 5.7 pm laser illumination at two selected polarization angles 9 = 20°and 110°FIG. 15F shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity under 5.7 pm laser illumination at two selected polarization angles 0 = 70°and 160°.FIG. 16A shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of polarization angle 0 (in degrees or deg) illustrating the variation of responsivity of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of polarization angle for different wavelengths.FIG. 16B shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of polarization angle 0 (in degrees or deg) illustrating the variation of responsivity of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of polarization angle for different wavelengths.FIG. 16C shows a two dimensional plot of the responsivity of the first homojunction HJ-1 (in milli-Amperes per Watt or mA W'1) as a function of the responsivity of the second homojunction HJ-2 (in milli-Amperes per Watt or mA W'1) of the optical detector (device 1) according to various embodiments such that the polarization and wavelength can be simultaneously determined under normalization of incident intensity.FIG. 17A shows an optical microscopy image of a bismuth selenite (BizOzSe) bolometric detector according to various embodimentsFIG. 17B shows a schematic illustrating the bismuth selenite (BizOzSe) bolometric detector according to various embodiments under mid infrared (MIR) light illumination.FIG. 17C shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the mid infrared (MIR) absorption of three bismuth selenite (BizOzSe) according to various embodiments, with the inset showing that the MIR absorptions of the three samples are similar in the 3 pm to 6 pm range.FIG. 17D shows a plot of current (in micro- Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (BizOzSe) bolometric detector according to various embodiments in the dark and under illumination of 3.7 pm laser. FIG. 17E shows a plot of current (in micro-Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (BizOzSe) bolometric detector according to various embodiments in the dark and under illumination of 4.6 pm laser. FIG. 17F shows a plot of current (in micro-Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (BizOzSe) bolometric detector according to various embodiments in the dark and under illumination of 5.7 pm laser. FIG. 17G shows a plot of current (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the bismuth selenite (BizOzSe) bolometric detector according to various embodiments.FIG. 17H shows a plot of resistance variation AR / R (in percent or %) as a function of polarization angle (in degrees or °) illustrating the resistance variation of the detector according to various embodiments under 3.7 pm laser illumination with different polarization angles.FIG. 171 shows a plot of resistance variation AR / R (in percent or %) as a function of power density (in Watts per square centimeters or W / cm2) illustrating the resistance variation of the detector according to various embodiments with incident intensity.FIG. 18A shows an optical microscopy image of an optical detector (device 2) according to various embodiments.FIG. 18B shows an atomic force microscopy (AFM) image illustrating the topology of the optical detector (device 2) according to various embodiments.FIG. 18C shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device2) according to various embodiments, which indicates that the crystal orientation differences of the left black arsenic phosphorus (L-AsP) flake and the right black arsenic phosphorus (R- AsP) flake relative to the middle black arsenic phosphorus (M-AsP) flake are determined to be -45° and -135°, respectivelyFIG. 18D shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the left black arsenic phosphorus (L-AsP) flake of the optical detector (device 2) according to various embodiments.FIG. 18E shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the middle black arsenic phosphorus (M-AsP) flake of the optical detector (device 2) according to various embodiments.FIG. 18F shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the right black arsenic phosphorus (R-AsP) flake of the optical detector (device 2) according to various embodiments.FIG. 19A shows the optical microscopy image of the first homojunction HJ-1 of the optical device (device 2) according to various embodimentsFIG. 19B shows a schematic of the photocurrent mapping measured from the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments. It can be observed that the photocurrent signs at positions 1, 2, 3, and 4 areand respectively.FIG. 19C shows a plot of the photocurrent IDS (in micro- Amperes or pA) as a function of drainsource voltage VDS (in volts or V) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments under large VDS bias voltage range (±1V) in the dark and under 532 nm laser illumination at position 2 (laser@2) and position 3 (laser@3).FIG. 19D shows a plot of the photocurrent IDS (in nano-Amperes or nA) as a function of drainsource voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments under VDS bias voltage range (±10 mV) in the dark and under 532 nm laser illumination at position 2 (laser@,2) and position 3 (laser@3).FIG. 20A shows a plot of photocurrents fos.i IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 6 is rotated from 0° to 180° with a step of 10° at Vos = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 1.9 W / cm2.FIG. 20B shows a plot of the photocurrents IDS,I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) at the incident intensity of 1.9 W / cm2.FIG. 20C shows a plot of photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 6.7 W / cm2.FIG. 20D shows a plot of the photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 6.7 W / cm2.FIG. 20E shows a plot of photocurrents IDS,I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 11.4 W / cm2. FIG. 20F shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) at the incident intensity of 11.4 W / cm2.FIG. 20G shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 18.1 W / cm2.FIG. 20H shows a plot of the photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 18.1 W / cm2.FIG. 201 shows a plot of photocurrents IDS,I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction Hl-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 23.9 W / cm2. FIG. 20J shows a plot of the photocurrents IDS,I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 23.9 W / cm2.FIG. 20K shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity ( / ') of 28.7 W / cm2. FIG. 20L shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 28.7 W / cm2.FIG. 21A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2.FIG. 2 IB shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the second homojunction (HJ-2) of the optical detector (device 2) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. 0° and 90° refer to the polarization angles of the incident light.FIG. 21C shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1 .9 W cm'2to 28.7 W cm'2).FIG. 2 ID shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2).FIG. 21E shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 2) according to various embodiments under 3.7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determined.FIG. 22A shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 4.6 pm laser illumination at different incident intensities (4.4 W cm'2to 16.7 W cm'2).FIG. 22B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 4.6 pm laser illumination at different incident intensities (4.4 W cm'2to 16.7 W cm'2). These photocurrents were measured at VDS = 0V.FIG. 22C shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 2) according to various embodiments under 4.6 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 4.4 W cm'2to 16.7 W cm'2can be simultaneously determined. These photocurrents were measured at VDS = 0V.FIG. 22D shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 5.7 pm laser illumination at different incident intensities (2.8 W cm'2to 34. 1 W cm'2).FIG. 22E shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities (2.8 W cm'2to 34.1 W cm'2). These photocurrents were measured at VDS = OV.FIG. 22F shows a two dimensional plot of the first photocurrent IDS.I (in nano- Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano- Amperes or nA) of the optical detector (device 2) according to various embodiments under 5.7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 2.8 W cm'2to 34.1 W cm'2can be simultaneously determined.FIG. 23A shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) of the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths.FIG. 23B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths. The polarization angle is fixed at 0 = 0°. These photocurrents may exhibit a linear dependence on the incident intensity. FIG. 23 C shows a plot of responsivity (in milli-Amperes per Watt or mA / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation responsivity of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.FIG. 23D shows a plot of responsivity (in milli-Amperes per W or mA / W) as a function of polarization angle 0 (in degrees or °) illustrating the variation of responsivity of the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments with polarization angle for different wavelengths.FIG. 23E shows a plot of responsivity (in milli-Amperes per W or mA / W) as a function of polarization angle 0 (in degrees or °) illustrating the variation of responsivity of the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with polarization angle for different wavelengths.FIG. 23F shows a two dimensional plot of the responsivity of the first homojunction HJ-1 (in milli-Amperes per Watt or mA / W) as a function of the responsivity of the second homojunction HJ-2 (in milli-Amperes per Watt or mA / W) of the optical detector (device 2) according to various embodiments such that the polarization and wavelength can be simultaneously determined under normalization of incident intensity.FIG. 24A shows a plot of noise current (in square Amperes per Hertz or A2 / Hz) as a function of frequency (in Hertz or Hz) illustrating variation of noise currents of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with frequency.FIG. 24B shows a plot of noise equivalent power NEP (in pico-Watts per square-root Hertz or pW / Hz°5) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the NEP of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 9 = 0°.FIG. 24C shows a plot of detectivity (xlO8centimeter square-root Hertz per Watt or cm Hz05 / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the detectivity of the first homojunction HJ-1 and the second homojunction HJ- 2 of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.FIG. 25A shows an optical microscopy image of an optical detector (device 3) according to various embodiments. The thickness of as-used b-AsP flakes is about 60 nm.FIG. 25B shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 3) according to various embodiments, which makes it possible to determine the crystal orientation of the b-AsP flake via Ag2 / Ag1(armchair or AC) > Ag2 / Ag1(zig-zag or ZZ).FIG. 25C shows a schematic illustrating that the crystal orientation differences of the left black arsenic phosphorus (L-AsP) flake and the right black arsenic phosphorus (R-AsP) flake relative to the middle black arsenic phosphorus (M-AsP) flake are determined to be -60° and -120°, respectively.FIG. 25D shows a plot of the first photocurrent IDS,I (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 3) according to various embodimentsas a function of polarization angle 9 (in degrees or °) under 3.7 gm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2).FIG. 25E shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2).FIG. 25F shows a two dimensional plot of the first photocurrent IDS,I (in nano- Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano- Amperes or nA) of the optical detector (device 3) according to various embodiments under 3.7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determinedFIG. 26A shows a plot of photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity P) of 1.9 W / cm2.FIG. 26B shows a plot of the photocurrents IDS,I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 9 (in degrees or °) at the incident intensity of 1.9 W / cm2.FIG. 26C shows a plot of photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity ( / ■’) of 6.7 W / cm2.FIG. 26D shows a plot of the photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 6.7 W / cm2.FIG. 26E shows a plot of photocurrents IDS.I IDS, 2 (in nano- Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to variousembodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 11.4 W / cm2. FIG. 26F shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 11.4 W / cm2.FIG. 26G shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 18.1 W / cm2. FIG. 26H shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 18.1 W / cm2.FIG. 261 shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 23.9 W / cm2. FIG. 26J shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or deg) at the incident intensity of 23.9 W / cm2.FIG. 26K shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 28.7 W / cm2. FIG. 26L shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device3) according to various embodiments as a function of polarization angle 0 (in degrees or deg) at the incident intensity of 28.7 W / cm2.FIG. 27A shows a plot of polarization angle 9 (in degrees or °) as a function of gate voltage KGS (in volts or V) illustrating the photocurrent map of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with 0 and KGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V.FIG. 27B shows a plot of polarization angle 0 (in degrees or °) as a function of gate voltage KGS (in volts or V) illustrating the photocurrent map of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with 0 and KGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V.FIG. 27C shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments at different polarization angles (0 = 0 - 180°) and gate voltage (KGS = 0, -20 and -40 V), demonstrating the electrically tunable polarization response characteristics.FIG. 27D shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of gate voltage KGS (in Volts or V) illustrating variation of responsivity of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with gate voltage at polarization angles 0 = 20° and 0 = 110°.FIG. 28A shows an optical microscopy image of an optical detector (device 4) according to various embodiments.FIG. 28B shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device4) according to various embodiments.FIG. 28C shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of drain-source bias VDS (in milli-Volts or mV) illustrating the output characteristics curves of the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments. FIG. 28D shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of drain-source bias VDS (in milli-Volts or mV) illustrating the output characteristics curves of the second homojunction HJ-2 of the optical detector (device 4) according to various embodiments.FIG. 28E shows a plot of the photocurrent IDS (in nano-Amperes or nA) / gate current IGS (in nano-Amperes or nA) as a function of gate voltage VGS (in Volts or V) illustrating the characteristic curves of the optical detector (device 4) according to various embodiments at drain-source bias VDS = 10 mV.FIG. 28F shows a plot of the photocurrent IDS (in nano-Amperes or nA) as a function of gate voltage VGS (in Volts or V) illustrating the characteristic curves of the optical detector (device 4) according to various embodiments at drain-source bias VDS = 0 V.FIG. 29A shows a plot of polarization angle 9 (in degrees or °) as a function of gate voltage VGS (in volts or V) illustrating the photocurrent map of the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments with 9 and VGS under 3.7 pm laser illumination with an incident intensity of 1 .9 W cm'2at drain-source bias VDS = 0 V.FIG. 29B shows a plot of polarization angle 9 (in degrees or °) as a function of gate voltage VGS (in volts or V) illustrating the photocurrent map of the second homojunction HJ-2 of the optical detector (device 4) according to various embodiments with 9 and VGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V.FIG. 29C shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the gate voltage VGS (in Volts or V) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments at polarization angles 9 = 0° and 9 = 90° (3.7 pm laser illumination with an incident intensity of 1.9 W cm'2), which increases with more negative gate voltage.FIG. 29D shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of polarization angle 9 (in degrees or °) illustrating the variation of the photocurrent at the first homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2with polarization angles at VGS = 0 V, -20 V and -40 V.FIG. 29E shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of polarization angle 9 (in degrees or °) illustrating the variation of the photocurrent at the second homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2with polarization angles at VGS = 0 V, -20 V and -40 V.FIG. 29F shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector(device 4) according to various embodiments under 3.7 gm laser illumination with an incident intensity of 1.9 W cm'2at different polarization angles (0 = 0 - 180°) and gate voltages (KGS = 0 V, -20 V and -40 V), demonstrating the electrically tunable polarization response characteristicsFIG. 30A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of polarization angle 0 (in degrees or °) illustrating the variation of the photocurrent at the first homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0. 15 W cm'2with polarization angle at KGS = 0 V and -40 V.FIG. 30B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of polarization angle 0 (in degrees or °) illustrating the variation of the photocurrent at the second homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0.15 W cm'2with polarization angle at KGS = 0 V and -40V.FIG. 30C shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0.15 W cm'2at different polarization angles (0 = 0 - 180°) and gate voltages ( KGS = 0 V and -40 V), demonstrating more accurate discrimination of polarization angles with a low incident intensity by applying a more negative gate voltage.FIG. 31A is a schematic illustrating a simple imaging set-up and data-processing method for image reconstruction according to various embodiments.FIG. 3 IB shows the measured photocurrent for the first homojunction HI-1 of the optical detector (device 1) according to various embodiments.FIG. 31C shows the measured photocurrent for the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments.FIG. 3 ID shows the reconstructed intensity information of the ‘N’, ‘T’ and ‘U’ targets obtained using the data-processing method according to various embodiments.FIG. 3 IE shows the reconstructed polarization angle information of the ‘N’, ‘T’ and ‘U’ targets obtained using the data-processing method according to various embodiments.FIG. 32A shows a plot of intensity P (in Watts per square centimeters or W / crn2) as a function of position comparing the reconstructed intensity information with pre-set intensity data (denoted by horizontal dashed lines) according to various embodiments.FIG. 32B shows a plot of polarization angle 0 (in degrees or °) as a function of position comparing the reconstructed polarization angle information with pre-set polarization angle data (denoted by horizontal dashed lines) according to various embodiments.FIG. 33 shows a table providing the value of constants A, B, C, D for different wavelengths according to various embodimentsDESCRIPTION

[0009] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0010] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0011] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0012] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e.g., within 10% of the specified value.

[0013] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0014] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0015] By “consisting of’ it is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0016] Embodiments described in the context of one of the optical detectors / systems are analogously valid for the other optical detectors / systems. Similarly, embodiments described in the context of a method are analogously valid for an optical detector / system, and vice versa.

[0017] Various embodiments may seek to address one or more issues faced by conventional optical detectors.

[0018] FIG. 1 shows a general illustration of an optical detector according to various embodiments. FIG. 2 shows a top planar view schematic of an optical detector according to various embodiments. The optical detector may include a first photosensitive element 102, 202 including a two-dimensional material. The optical detector may also include a second photosensitive element 104, 204 including the two-dimensional material, the second photosensitive element 104, 204 forming a first homojunction with the first photosensitive element 102, 202. The optical detector may further include a third photosensitive element 106, 206 including the two-dimensional material, the third photosensitive element 106, 206 forming a second homojunction with the first photosensitive element 102, 202. An armchair (AC) orientation of the first photosensitive element 102, 202 may be along a first direction, while an armchair orientation (AC) of the second photosensitive element 104, 204 may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element 106, 206 may be along a third direction different from the first direction and different from the second direction

[0019] In other words, the optical detector may include three photosensitive elements 102 - 106, 202 - 206 with armchair (AC) orientations in different directions. The first photosensitive element 102, 202 may contact the second photosensitive element 104, 204 to form a first homojunction, and may also contact the third photosensitive element 106, 206 to form a second homojunction.

[0020] FIG. 1 provides a general illustration of the optical detector including the features according to various embodiments, while FIG. 2 provides a schematic of one possibleimplementation of the optical detector according to various embodiments. In this regard, FIG. 2 is not intended to limit, for instance, the shape, size, orientation, arrangement etc. of the features. For instance, while FIG. 2 shows the photosensitive elements 202 - 206 forming an “U” shape, various other embodiments may relate to an optical detector with photosensitive elements arranged in any suitable manner and in any suitable orientation, such an inverted “U” shape.

[0021] In various embodiments, the optical detector may be a photothermoelectric detector. In other words, the optical detector may operate based on the photothermoelectric effect. The optical detector may be configured to operate in mid-infrared (MIR) regime. Each of the first photosensitive element 102, 202, the second photosensitive element 104, 204 and the third photosensitive element 106, 206 may be configured to generate heat in response to light, e g., MIR light, incident on the photosensitive element, which may in turn generate a photocurrent due to the Seebeck effect. The MIR light may, for instance, be of a wavelength or range of wavelengths selected from a range from 3 pm to 10 pm.

[0022] In various embodiments, the second direction may be at an angle of al degrees relative to the first direction, while the third direction may be at an angle of a2 degrees relative to the first direction, a2 degrees being equal to 180 degrees subtracted by al degrees. In other words, in various embodiments, when the AC orientation of the second photosensitive element 104, 204 is al degrees relative to the AC orientation of the first photosensitive element 102, 202, the AC orientation of the third photosensitive element 106, 206 may be 180 - al degrees relative to the AC orientation of the first photosensitive element 102, 202, i.e., a2 = 180 - al.

[0023] In various embodiments, the orientations of the photosensitive elements 102 - 106, 202 - 206 may not exactly follow the abovementioned relationship. For instance, when the AC orientation of the second photosensitive element 104, 204 is al degrees relative to the AC orientation of the first photosensitive element 102, 202, the AC orientation of the third photosensitive element 106, 206 may be at any angle within a range of 180 - al ± 10 degrees, e.g., a range of 180 - al ± 5 degrees relative to the AC orientation of the first photosensitive element 102, 202.

[0024] In various embodiments, a thickness of the first photosensitive element 102, 202, a thickness of the second photosensitive element 104, 204 and a thickness of the third photosensitive element 106, 206 may substantially be equal. In the current context, the term “substantially” may refer to a variance of ±5 %. In other words, in various embodiments, athickness of the first photosensitive element 102, 202, a thickness of the second photosensitive element 104, 204 and a thickness of the third photosensitive element 106, 206 may be within a value selected from a range from 95% to 105% of one another.

[0025] In various embodiments, a size of the first photosensitive element 102, 202, a size of the second photosensitive element 104, 204 and a size of the third photosensitive element 106, 206 may substantially be equal. In other words, a size of the first photosensitive element 102, 202, a size of the second photosensitive element 104, 204 and a size of the third photosensitive element 106, 206 may be within a value selected from a range from 95% to 105% of one another.

[0026] Having similar thicknesses and / or sizes may help avoid photothermoelectric or photovoltaic effects induced by asymmetric geometries.

[0027] In various embodiments, the two-dimensional material may be any 2D layered material with in-plane anisotropic crystal structure. For instance, the two-dimensional material may be any one selected from a group consisting of black arsenic-phosphorous (bAsP), black phosphorous (bP), palladium selenide (I’dScj), tantalum iridium telluride (TaIrTe4), tellurium (Te) and tantalum nickel selenide (Ta2NiSes).

[0028] In various embodiments, each of the first photosensitive element 102, 202, the second photosensitive element 104, 204 and the third photosensitive element 106, 206 may be a flake (with a regular or an irregular shape) including one or more monolayers. In various other embodiments, it may be envisioned that the first photosensitive element 102, 202, the second photosensitive element 104, 204 and the third photosensitive element 106, 206 may be of any other suitable structures, such as nanowires or nanoribbons.

[0029] In various embodiments, the optical detector may further include a substrate. The optical detector may also include an insulating (or dielectric) layer on the substrate such that the first photosensitive element 102, 202, the second photosensitive element 104, 204 and the third photosensitive element 106, 206 are on the insulating (or dielectric) layer. In other words, the substrate may be separated or spaced apart from the first photosensitive element 102, 202, the second photosensitive element 104, 204 and the third photosensitive element 106, 206 by the insulating layer. In various embodiments, the insulating or dielectric layer may be insulating and insensitive to incident light. The insulating or dielectric layer may include any suitable materials, such as silicon oxide (SiCh), or calcium fluoride (CaFi). The substrate may include any suitable semiconductor material such as silicon.

[0030] In various embodiments, the optical detector may also include a first electrode in contact with the first photosensitive element 102, 202. The optical detector may further include a second electrode in contact with the second photosensitive element 104, 204. The optical detector may additionally include a third electrode in contact with the third photosensitive element 106, 206. The first electrode, the second electrode, and the third electrode may each include one or more suitable electrically conductive material, such as chromium (Cr), gold (Au), or silver (Ag).

[0031] In various embodiments, the optical detector may be configured to determine a polarization angle and an intensity of a light incident onto the optical detector by measuring a first photocurrent flowing through the first homojunction and a second photocurrent flowing through the second homojunction. In various embodiments, the optical detector may include one or more current detectors, e.g., ammeters, to measure or detect the first photocurrent and the second photocurrent. In various other embodiments, the optical detector may be part of a system which may include the one or more current detectors. In various embodiments, the optical detector or the system may include a first ammeter in electrical connection or contact with the second electrode, and a second ammeter in electrical connection or contact with the third electrode.

[0032] In various embodiments, the optical detector may be configured to determine the polarization angle and a wavelength of the light incident onto the optical detector by determining a first responsivity of the first homojunction and a second responsivity of the second homojunction. In various other embodiments, the system may include a processor in communication with the optical detector. The processor may be configured to determine the polarization angle and a wavelength of the light incident onto the optical detector by determining a first responsivity of the first homojunction and a second responsivity of the second homojunction.

[0033] In other words, in various embodiments, the optical detector may include an onboard processor configured to determine or calculate the first responsivity of the first homojunction, the second responsivity of the second homojunction, the polarization angle, the intensity of the light, and / or the wavelength of the light based on the first responsivity and the second responsivity In various other embodiments, the system may include the separate processor, which may be in communication with the optical system (e.g., via wired or wireless means), and which may be configured to determine or calculate the first responsivity of the firsthomojunction, the second responsivity of the second homojunction, the polarization angle, the intensity of the light, and / or the wavelength of the light based on the first responsivity and the second responsivity.

[0034] Tn various embodiments, the optical detector may include a first source and a first drain associated with the first homojunction, the first source and the first drain configured to be biased with a first potential difference between the first source and the first drain. The optical detector may include a second source and a second drain associated with the second homojunction, the second source and the second drain configured to be biased with a second potential difference between the second source and the second drain. Various embodiments may include one or more electrical biasing voltage sources for providing the first potential difference and / or the second potential difference. Tn various embodiments, the first potential difference may be 0 V, and the second potential difference may be 0 V. In various embodiments, the first electrode may be or function as both the first source and the second source. The second electrode may be or function as the first drain, while the third electrode may be or function as the second drain.

[0035] In various embodiments, the substrate may act as a gate electrode. A biasing gate voltage may be applied to the substrate for tuning electrical conductivity of the first homojunction and the second homojunction. Various embodiments may include a gate biasing voltage source for providing the biasing gate voltage.

[0036] FIG. 3 shows a general illustration of a method of forming an optical detector according to various embodiments. The method may include, in 302, forming a first photosensitive element including a two-dimensional material. The method may also include, in 304, fonning a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The method may additionally include, in 306, forming a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element. An armchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.

[0037] In other words, the method of forming the optical detector may include forming the first photosensitive element, the second photosensitive element and the third photosensitive element with their AC orientations in different directions.

[0038] For avoidance of doubt, FIG. 3 is not intended to limit the sequence of the various steps. For instance, step 302 may occur before, after or at the same time as step 304.

[0039] In various embodiments, the second direction may be at an angle of al degrees relative to the first direction, while the third direction may be at an angle of a2 degrees relative to the first direction, a2 degrees being equal to 180 degrees subtracted by al degrees.

[0040] In various embodiments, a thickness of the first photosensitive element, a thickness of the second photosensitive element and a thickness of the third photosensitive element may substantially be equal

[0041] In various embodiments, a size of the first photosensitive element, size of the second photosensitive element and a size of the third photosensitive element may substantially be equal.

[0042] In various embodiments, the two-dimensional material may be any one selected from a group consisting of black arsenic-phosphorous (bAsP), black phosphorous (bP), palladium selenide (PdSe?), tantalum iridium telluride (TaIrTe4), tellurium (Te) and tantalum nickel selenide (TazNiSes).

[0043] In various embodiments, each of the first photosensitive element, the second photosensitive element and the third photosensitive element may be a flake including one or more monolayers.

[0044] In various embodiments, the first photosensitive element, the second photosensitive element and the third photosensitive element may be formed over a substrate. The method may include forming an insulating (or dielectric) layer on the substrate. The method may include forming the first photosensitive element, the second photosensitive element and the third photosensitive element on the insulating (or dielectric) layer.

[0045] In various embodiments, the method may include forming a first electrode in contact with the first photosensitive element. The method may also include forming a second electrode in contact with the second photosensitive element. The method may additionally include forming a third electrode in contact with the third photosensitive element

[0046] In various embodiments, the optical detector may be configured to determine a polarization angle and an intensity of a light incident onto the optical detector by measuring afirst photocurrent flowing through the first homojunction and a second photocurrent flowing through the second homojunction.

[0047] In various embodiments, the optical detector may be configured to determine the polarization angle and a wavelength of the light incident onto the optical detector by determining a first responsivity of the first homojunction and a second responsivity of the second homojunction.

[0048] In various embodiments, the optical detector may include a first source and a first drain associated with the first homojunction, the first source and the first drain configured to be biased with a first potential difference between the first source and the first drain. The optical detector may include a second source and a second drain associated with the second homojunction, the second source and the second drain configured to be biased with a second potential difference between the second source and the second drain.

[0049] In various embodiments, the substrate may act as a gate electrode. A biasing gate voltage may be applied to the substrate for tuning electrical conductivity of the first homojunction and the second homojunction. In various embodiments, a gate biasing voltage source may be provided for providing the biasing gate voltage.

[0050] FIG. 4 shows a general illustration of a method of operating an optical detector according to various embodiments. The method may include, in 402, providing a light to the optical detector. The optical detector may include a first photosensitive element include a two- dimensional material. The optical detector may also include a second photosensitive element including the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element. The optical detector may further include a third photosensitive element including the two-dimensional material, the third photosensitive element forming a second homoj unction with the first photosensitive element. The method may also include, in 404, determining a first photocurrent flowing through the first homojunction. The method may additionally include, in 406, determining a second photocurrent flowing through the second homojunction. An armchair (AC) orientation of the first photosensitive element may be along a first direction, while an armchair orientation (AC) of the second photosensitive element may be along a second direction different from the first direction, and an armchair orientation of the third photosensitive element may be along a third direction different from the first direction and different from the second direction.

[0051] In other words, various embodiments to operate the optical detector as described herein may include providing light to the optical detector, as well as determining or measuring the first photocurrent flowing through the first homojunction and the second photocurrent flowing through the second homojunction.

[0052] In various embodiments, step 402 may occur before or at the same time as steps 404 and step 406. Step 404 may occur before, after or at the same time as step 406.

[0053] In various embodiments, the optical detector may be configured to determine a polarization angle and an intensity of the light incident onto the optical detector based on the first photocurrent and the second photocurrent.

[0054] In various embodiments, the method may include determining a first responsivity of the first homojunction based on the first photocurrent. The method may also include determining a second responsivity of the second homojunction based on the second photocurrent. The optical detector may be configured to determine the polarization angle and a wavelength of the light incident onto the optical detector based on the first responsivity and the second responsivity.

[0055] In various embodiments, the method may also include applying a first potential difference between a first source and a first drain associated with the first homojunction before determining the first photocurrent flowing through the first homojunction. The method may further include applying a second potential difference between a second source and a second drain associated with the second homojunction before determining the second photocurrent flowing through the second homojunction.

[0056] In various embodiments, the method may additionally include applying a biasing gate voltage to a substrate. The substrate may be separated or spaced apart from the first photosensitive element, the second photosensitive element and the third photosensitive element by an insulating (or dielectric) layer.

[0057] Various embodiments may relate to a device operated in the mid-infrared (MIR) regime at room temperature, with the device demonstrating multidimensional optical detection. The device may include double twisted black arsenic-phosphorus (b-AsP) homojunctions and may work at zero bias by virtue of the photothermoelectric effect. The bipolar and phase-offset polarization photoresponse of the double twisted b-AsP homojunctions may enable unambiguous detection of linear polarization angles from 0° to 180°. More importantly, simultaneous detection of polarization angle and incident intensity may be realized by directlymeasuring the photocurrents generated from the double twisted b-AsP homojunctions under uniform and global illumination. The wavelength coupled with polarization angles can also be extracted from the responsivity of the device. The responsivity, detectivity and response speed of the device at zero bias may reach ~50 mAW-1, ~1.2 109cm Hz°3W-1and~20 ps, respectively. The responsivity of the device may be enhanced to~150 mAW’1by applying a gate field, which is favorable for distinguishing polarization angles more accurately in low- light-intensity irradiation conditions. In addition, the device may exhibit highly accurate image reconstruction of multidimensional information, which provides a promising platfonn for compact, miniaturized and multifunctional photodetectors.

[0058] FIG. 5 A shows a schematic of an optical detector according to various embodiments. The optical detector may include a middle b-AsP flake (also referred to as M-AsP) 502, a right b-AsP flake (also referred to as R-AsP) 504, and a left b-AsP flake (also referred to as L-AsP) 506. The L-AsP 506 and the R-AsP 504 may be twisted by 45° and 135° as compared to the M-AsP 502 respectively. The armchair (AC) orientations of the flakes are marked in FIG. 5A. The M-AsP 502 and the R-AsP 504 may form a first homojunction (HJ-1), while the M-AsP 502 and the L-AsP 506 may form a second homojunction (HJ-2). E, k and 0 are the electric magnitude, wave vector and polarization angle of the incident MIR light, respectively, and I7GS is the gate voltage. The photocurrents (IDS,I and IDS, 2) are measured under zero drain-source bias (VDS.I = VDS.Z = 0 V). The optical detector may also include a first electrode 508, a second electrode 510 and a third electrode 512 in contact with the flakes 502, 504, 506 respectively. The flakes 502, 504, 506 and the electrodes 508, 510, 512 may be over a substrate 514a. The substrate 514a may include a semiconductor material such as silicon (Si). The optical detector may also include an insulating (or dielectric) layer 514b separating the substrate 514a and the flakes 502, 504, 506. The insulating (or dielectric) layer 514b may include a material such as silicon oxide (SiOz). =

[0059] FIG. 5B shows (above) a perspective view and (below) a top view illustrating the anisotropic structure of black arsenic phosphorus (b-AsP) according to various embodiments. The As atoms may be randomly distributed in the crystal structure. The armchair (AC) and zigzag (ZZ) orientations are also shown.

[0060] The anisotropic structure and the narrow bandgap (~0.2 eV) of b-AsP may provide distinct anisotropic optical absorption in the MIR region. In addition, b-AsP confers excellent thermoelectric properties with a large Seebeck coefficient of -723 gVK-1, enabling asignificant photothermoelectric effect in the device. The three b-AsP photosensitive elements 502, 504, 506 used in the device may be of similar thicknesses and sizes to avoid photothermoelectric or photovoltaic effects induced by asymmetric geometries. For photoresponse measurements, the device operating at zero drain-source bias (VDS = 0 V) is globally illuminated by a wavelength-tunable MIR quantum cascaded laser with a spot diameter of around 100 pm. The polarization angle of incident light may be controlled by rotating a half-wave plate.

[0061] FIG. 5C shows schematics illustrating the predicted photocurrent signs in the optical detector according to various embodiments under illumination with different polarization angles. FIG. 5D shows plots of absorption / temperature and hole concentrations illustrating the absorption, temperature and hole concentration profiles of the various flakes 502, 504, 506 of the optical detector according to various embodiments under illumination of light at polarization angles 0 = 0° and 90°. Under uniform illumination with 0 = 0°, the polarization direction of incident light is parallel to the AC orientation of M-AsP 502. The optical absorption of M-AsP 502 may be stronger than that of L-AsP 506 and R-AsP 504 due to the intrinsic anisotropic properties, which give rise to a higher temperature and larger carrier concentrations (holes for p-type b-AsP) in M-AsP 502 due to the photothermal effect, as shown in the upper part of FIG. 5D In this case, the temperature gradient and the carrier concentration gradient may drive hole diffusion from M-AsP 502 to L-AsP 506 and R-AsP 504, thus forming positive photocurrents from source (S) to drain (D) in both HJ-1 and HJ-2 (IDSJ > 0, IDS, 2 > 0). The black curve arrows in FIG. 5D show the direction of hot carrier diffusion.

[0062] For 9 = 45°, the polarization direction of the incident light may be parallel to the AC orientation of L-AsP 506, and perpendicular to that of R-AsP 504. The optical absorption (corresponding to the temperature and the carrier concentrations) may present a trend of L- AsP 506 > M-AsP 502 > R-AsP 504, which results in the diffusion of carriers from L-AsP 506 to M-AsP 502 in HJ-2 (IDS, 2 < 0) and from M-AsP 502 to R-AsP 504 in HJ-1 (IDS,i > 0).

[0063] Analogously, the diffusion direction of the photoexcited carriers at 0 = 90° (IDSJ < 0, IDS2< 0) is opposite to 9 = 0°, as shown at the bottom of FIG. 5D. FIG. 5D shows negative photocurrents may be formed at 9 = 90°.

[0064] For 9 = 135°, IDSJ < 0 and IDS, 2 > 0, which are contrary to those for 0 = 45°.

[0065] FIG. 5E shows a two-dimensional plot of predicted first photocurrent (IDS. / ) as a function of predicted second photocurrent (IDS, 2) of the optical detector according to variousembodiments at different polarization angles (9) and incident intensities (P), which enables simultaneous detection of 9 and P. From the plot with a closed curve, the polarization angle can be unambiguously determined at a certain incident intensity (P). It should be noted that the signs of the photocurrents may depend on the polarization angle, while the values of the photocurrents may be determined by the polarization angle and the incident intensity. As a result, the closed curve would expand with increasing incident intensity. Therefore, the polarization angle and incident intensity of an unknown linear polarization MIR. light may be simultaneously detected using the double twisted b-AsP homojunctions.

[0066] A typical device (device 1) was fabricated using mechanically exfoliated b-AsP flakes. FIG. 6A shows an optical microscopy image of an optical detector (device 1) according to various embodiments. FIG 6B shows an atomic force microscopy (AFM) image illustrating the topology of the optical detector (device 1 ) according to various embodiments. The thickness of these b-AsP flakes was determined to be —120 nm. The AC orientation of the three b-AsP flakes was determined by polarized Raman spectroscopy. FIG. 6C shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the left black arsenic phosphorus (L-AsP) flake of the optical detector (device 1) according to various embodiments. FIG. 6D shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the middle black arsenic phosphorus (M- AsP) flake of the optical detector (device 1) according to various embodiments. FIG. 6E shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the right black arsenic phosphorus (R-AsP) flake of the optical detector (device 1) according to various embodiments. The peak positions of Ag1, fhg, and Ag2vibration modes are located at -360 cm'1, -440 cm'1, and -460 cm'1, respectively.

[0067] FIG. 6F shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 1) according to various embodiments, which makes it possible to determine the crystal orientation of the b-AsP flake via Ag2 / Ag1(armchair or AC) > Ag2 / Ag1(zig-zag or ZZ). The maximum ratio corresponds to the AC orientation of a b-AsP flake. The crystal orientation differences of the L-AsP flake and the R-AsP flakes relative to the M-AsP flake may be determined to be -45° and -135°, respectively. In other words, the twist angle between the M-AsP flake and the L-AsP flake may be determined to be -45°, while that between the M-AsP flake and the R-AsP flake may be determined to be -135°.

[0068] In addition, the b-AsP with a thickness of ~ 126 nm exhibits a remarkable anisotropic optical absorption in the mid-infrared (MIR) region. FIG. 6G shows the anisotropic optical absorption of a black arsenic phosphorous (b-AsP) flake (-126 nm thick) according to various embodiments at a wavelength X = 3.7 pm. FIG 7A shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of a black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of- 55 nm for polarization angles from 0° to 90°, with the inset showing a microscopy optical image of the b-AsP flake. FIG. 7B shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 7A according to various embodiments for polarization angles from 100° to 180°. FIG. 7C shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 7A according to various embodiments for polarization angles from 190° to 270°. FIG. 7D shows a plot of transmission (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical transmission spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 7A according to various embodiments for polarization angles from 280° to 350°. FIG. 7E shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of- 55 nm for polarization angles from 0° to 90°. FIG. 7F shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 100° to 180°. FIG. 7G shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 190° to 270°. FIG. 7H shows a plot of reflection (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical reflection spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 280° to 350°. FIG. 71 shows a plot of absorption (inpercent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of- 55 nm for polarization angles from 0° to 90°. FIG. 7J shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments for polarization angles from 100° to 180°. FIG. 7K shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b- AsP) flake according to various embodiments for polarization angles from 190° to 270°. FIG. 7L shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b- AsP) flake according to various embodiments for polarization angles from 280° to 350°. FIG. 7M shows the anisotropic optical absorption of a black arsenic phosphorous (b-AsP) flake (-55 nm thick) according to various embodiments at a wavelength Z = 3.7 pm. The absorption in the AC direction may be nearly twice that in the ZZ direction. FIG. 7N shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the optical absorption in the armchair (AC) orientation of black arsenic phosphorous (b-AsP) flakes with different thicknesses according to various embodiments The MIR absorption of the -126 nm b-AsP flake may be stronger than that of the -52 nm b-AsP flake. FIG. 70 shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake according to various embodiments with a thickness of - 126 nm for polarization angles from 0° to 90°, with the inset showing a microscopy optical image of the b-AsP flake. FIG. 7P shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the polarized optical absorption spectra of the black arsenic phosphorous (b-AsP) flake shown in FIG. 70 according to various embodiments for polarization angles from 105° to 165°.

[0069] From FIGS. 6G and 7A-P, the absorption along the AC orientation may be about twice that of the zigzag (ZZ) orientation, which is consistent with the previous reports.

[0070] After characterizing the crystal orientation and optical absorption of the devices, their photoresponse characteristics may be further demonstrated. Note that all devices were encapsulated by thick hexagonal boron nitride flakes to prevent oxidation in the air. The initialpolarization angle (0 = 0°) of incident light is fixed along the AC orientation of M-AsP. FIG. 8A shows a plot of the first photocurrent IDS.I (in micro- Amperes or pA) as a function of drainsource voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. FIG. 8B shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. 0° and 90° refer to the polarization angles of the incident light.

[0071] FIG. 8C shows a plot of the first photocurrent IDS.I (in micro-Amperes or pA) as a function of drain-source voltage VDS (in volts or V) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments under large VDS bias voltage range (±1V) in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. FIG. 8D shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) as a function of drain-source voltage VDS (in volts or V) illustrating the IDS - VDS characteristics of the second homojunction (HJ-2) of the optical detector (device 1 ) according to various embodiments under large VDS bias voltage range (±1 V) in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. FIG. 8E shows a plot of the first photocurrent IDS.I (in micro-Amperes or pA) as a function of gatesource voltage VGS (in volts or V) illustrating the transfer characteristics of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments under dark and a drain-source voltage VDS of 10 mV. FIG. 8F shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) as a function of gate-source voltage GS (in volts or V) illustrating the transfer characteristics of the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments under dark and a drain-source voltage VDS of 10 mV.

[0072] FIGS. 8C - F show the electrical properties of the device with linear IDS-VDS characteristics for a large bias voltage range (±1V) and high carrier (hole) mobility up to 620 cm2V-1s-1, suggesting negligible Schottky barriers exist between b-AsP and gold electrodes. In addition, the contact barrier height of b-AsP / Au was evaluated to be 35 meV, indicating that the photovoltaic effect induced by the Schottky barrier may be negligible. TheIDS-VDS lines under illumination with 0 = 0° and 90° shift opposite to the lines in the dark, and opposite photocurrents can be observed at zero bias (VDS = 0 V). Specifically, the IDS.I (IDS, 2) is + 1,280 nA (+1,198 nA) and -1,099 nA (-1,057 nA) for 0 = 0° and 90°, respectively. The positive and negative photocurrent signals may be consistent with the inference in FIGS. 5C- D, and may support the mechanism that the photothermoelectric photoresponse dominates. Moreover, scanning photocurrent mappings at zero bias (VDS = 0 V) provide direct evidence of the photothermoelectric effect in the devices.

[0073] FIG. 9A shows a schematic of the photocurrent mapping measured from the second homojunction (HJ-2) of the optical detector (device 1) according to various embodiments. FIG. 9B shows the simplified diagram of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments. FIG. 9C shows the qualitative band diagram of the first homojunction (HJ-1) of the optical detector (device 1) according to various embodiments. FIG. 9D shows a schematic diagram of carrier flow dominated by photovoltaic (PV) effect according to various embodiments. The photocurrent signs at positions 1 - 4 are marked as “-++”. FIG. 9E shows a schematic diagram of carrier flow dominated by the photothermoelectric (PTE) effect according to various embodiments The photocurrent signs at position 1 - 4 are marked as “-+-+”. The PTE effect may be well matched with the results of photocurrent mapping.

[0074] FIG. 10A shows a plot of photocurrents IDS.I IDS, 2 (in micro- Amperes or pA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 28.7 W cm-2. It is observed that both HJ-1 and HJ-2 demonstrate a bipolar photoresponse and the polarization ratio (PR = iDs.max / Ios, mm) is about -1.1.

[0075] FIG. 10B shows a plot of the first photocurrent IDS.I (in micro- Amperes or pA) exhibited by the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or deg) under 3.7 pm laser illumination at different incident intensities (1.9, 6.7, 11.4, 18.1, 23.9 and 28.7 W cm-2). FIG. 10C shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) exhibited by the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or deg) under 3.7 pm laser illumination atdifferent incident intensities (1.9, 6.7, 11.4, 18.1, 23.9 and 28.7 W cm-2). These photocurrents were measured at VDS = OV.

[0076] FIG. 10D shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 3.7 pm laser illumination at different low incident intensities (0.05. 0.1, 0.3 and 0.5 W cm-2). FIG. 10E shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 3.7 pm laser illumination at different low incident intensities (0.05. 0.1, 0.3 and 0.5 W cm-2).

[0077] The polarization-angle-dependent photocurrent curves that can be fitted well with cosine functions show an ~45°phase offset, and the photocurrents are linearly proportional to the incident intensity. FIG. 10F shows a plot of the first photocurrent IDS.I (in micro- Amperes or A) exhibited by the optical detector (device 1) according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrents of the optical detector (device 1) according to various embodiments with incident intensity under 3.7 pm laser illumination at two selected polarization angles 0 = 20° and 110°. FIG. 10G shows a plot of the second photocurrent IDS, 2 (in micro-Amperes or pA) exhibited by the optical detector according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrents of the optical detector (device 1) according to various embodiments with incident intensity under 3.7 pm laser illumination at two selected polarization angles 9 = 70° and 160°. The corresponding responsivities are listed next to the lines.

[0078] Therefore, by plotting the polarization-angle-dependent photocurrents of HJ-1 and HJ-2 at different incident intensities in 2D coordinates, the polarization angle and incident intensity may simultaneously and unambiguously be read out. FIG. 10H shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent I S, 2 (in nano-Amperes or nA) of the optical detector (device 1 ) according to various embodiments under 3.7 pm laser illumination for different intensities and polarization angles such that the polarization angle from 0° to 180° and incident intensity from 0.05 W / cm2to 0.5 W / cm2can be simultaneously determined. FIG. 101 shows a two dimensional plot of the first photocurrent IDS.I (in micro-Amperes or A) as a function of the second photocurrent IDS, 2 (in micro-Amperes or pA) of the optical detector (device 1)according to various embodiments under 3.7 gm laser illumination for different intensities and polarization angles such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determined.

[0079] This feature may be useful for optical communication applications, such as information decoding for polarization-division multiplexing.

[0080] The wavelength-dependent photoresponse of device 1 may be evaluated at zero external bias (VDS = 0 V). Under illumination at wavelengths of 3.7 pm, 4.6 pm and 5.7 pm and a fixed polarization angle of 9 = 0°, the device may be able to demonstrate stable and repeatable photoswitching response. FIG. 11 A shows a plot of the photocurrent IDS (in micro- Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the first homojunction HJ-1 of the optical detector (device 1 ) according to various embodiments to different wavelengths with a polarization angle of 0° at drain-source bias VDS = 0 V. The incident intensity dependence of the photocurrents of HJ-1 and HJ-2 for different illuminated wavelengths is shown in FIGS. 1 IB - G. FIG. 1 IB shows a plot of the first photocurrent IDS.I (in nano- Amperes or nA) of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of the power density (in Watts per square centimeter or W cm'2) illustrating the variation of photocurrent with power density at different wavelengths with polarization angle 0 = 0°, showing a linear dependence on intensity (IDS

[0081] FIG. 11C shows a plot of photocurrent I S (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) according to various embodiments for 3.7 pm laser illumination. FIG. 1 ID shows a plot of photocurrent IDS (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments for 3.7 pm laser illumination. FIG. 1 IE shows a plot of photocurrent IDS (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) according to various embodiments for 4.6 pm laser illumination. FIG. 1 IF shows a plot of photocurrent IDS (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the optical detector (device 1) according to various embodiments for 4.6 pm laser illumination. FIG. 11G shows a plot of photocurrent IDS (in Amperes or A) as a function of time (in seconds or s) illustrating the intensity-dependent photoresponse of the optical detector (device 1) accordingto various embodiments for 5.7 um laser illumination. FIG. 11H shows a plot of photocurrent IDS (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time- resolved photoresponse of the optical detector (device 1) according to various embodiments for 5.7 pm laser. All data were acquired at 0 = 0°.

[0082] The photocurrents of HJ-1 and HJ-2 show linear dependence (IDS X P1) within the measured intensity range. The responsivity (R) is extracted as R = IDS / ( / 'XA), where A is the effective area of the homojunctions (AHJ-I ~AHJ-2 ~ 105 pm2). FIG. 12A shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths.

[0083] FIG. 12B shows a plot of responsivity (in milli-Amperes per Watt or mA / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation responsivity of the optical detector (device 1) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.

[0084] As can be seen from FIG. 12B, the responsivity of the double homojunctions may remain approximately constant for different incident intensities, but may shows an increase with decreasing wavelengths, approaching ~45.6 mAW"1and 41.2 mAW"1for HJ-1 and HJ- 2, respectively, at 3.7 pm and 0 = 0°. FIG. 12C shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of wavelength (in micro-meters or pm) illustrating the wavelength-dependent responsivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments for polarization angle 0 = 0° and drain-source bias VDS = 0V. It may be seen from FIG. 12C that the responsivity increases when wavelength decreases. The dependence of responsivity on wavelength may be attributed to the stronger optical absorption of b-AsP for the shorter wavelengths.

[0085] FIG. 12D shows a plot of noise current (in square Amperes per Hertz or A2 / Hz) as a function of frequency (in Hertz or Hz) illustrating variation of noise currents of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with frequency. FIG. 12E shows a plot of noise equivalent power NEP (in pico-Watts per square-root Hertz or pW / Hz°=) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the NEP of the firsthomojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.

[0086] FIG. 12F shows a plot of detectivity (x 109centimeter square-root Hertz per Watt or cm Hz0 5 / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the detectivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity for different wavelengths at polarization angle 9 = 0°. FIG. 12G shows a plot of detectivity (x 109cm centimeter square-root Hertz per Watt or cm Hz°5 / W) as a function of wavelength (in micrometer or pm) illustrating the wavelength-dependent detectivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments for polarization angle 0 = 0° and drain-source bias VDS = 0V As shown in FIG 12G, the detectivity of the device can reach up to ~1 .2 x 109cm Hz05W’ ~7 x 108em Hz05W'1and ~4 x 108cm Hz°5W'1for wavelengths of 3.7 pm, 4.6 pm and 5.7 pm, respectively. Additionally, the response speed was evaluated to be ~20 ps, which may be comparable to that of a previously reported black phosphorus homojunction photodetector dominated by the photothermoelectric effect. FIG. 13 A shows a plot of normalized voltage (in arbitrary units or a.u.) as a function of time (in milli-seconds or ms) illustrating the time- resolved photoresponse of the optical detector (device 1) according to various embodiments. FIG. 13B shows a plot of normalized voltage (in arbitrary units or a.u.) as a function of time (in milli-seconds or ms) illustrating the response time with a rising time of ~21 ps and a decay time of ~17 ps of the optical detector (device 1) according to various embodiments. The data shown in FIGS. 13A-B were measured at zero bias and under 3.7 pm laser illumination.

[0087] The polarization-dependent photocurrents of the device may be characterized for different wavelengths with varied incident intensities. Similar to FIGS. 10H-I, the polarization angle and incident intensity can be unambiguously determined by measuring the photocurrents of HJ-1 and HJ-2 at a given incident wavelength.

[0088] FIG. 14A shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 9 (in degrees or °) under 4.6 pm laser illumination at different incident intensities from 0.2 W / cm2to 16.7 W / cm2. FIG. 14B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to variousembodiments as a function of polarization angle 0 (in degrees or °) under 4.6 pm laser illumination at different incident intensities from 0.2 W / cm2to 16.7 W / cm2. FIG. 14C shows a two dimensional plot of the first photocurrent Ios,i (in nano- Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 4.6 pm laser illumination for different intensities from 2.0 W / cm2to 16.7 W / cm2and polarization angles 0° to 180°. FIG. 14D shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 4.6 pm laser illumination for different intensities of 0.2 W / cm2and 0.9 W / cm2and polarization angles 0° to 180°. FIG. 14E shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with incident intensity under 4.6 pm laser illumination at two selected polarization angles 0 = 20°and 110°. FIG. 14F shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity under 4.6 pm laser illumination at two selected polarization angles 0 = 70°and 160°.

[0089] FIG. 15A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities from 0.6 W / cm2to 34.1 W / cm2. FIG. 15B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities from 0.6 W / cm2to 34.1 W / cm2. FIG. 15C shows a two dimensional plot of the first photocurrent 1DS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments under 5.7 pm laser illumination for different intensities from 6.9 W / cm2to 34.1 W / cm2and polarization angles 0° to 180°. FIG. 15D shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) accordingto various embodiments under 5.7 pm laser illumination for different intensities of 0.6 W / cm2, 1.5 W / cm2, and 2.8 W / cm2and polarization angles 0° to 180°. FIG. 15E shows a plot of the first photocurrent IDS.I (in nano- Amperes or nA) exhibited by the optical detector according to various embodiments as afunction of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with incident intensity under 5.7 pm laser illumination at two selected polarization angles 9 = 20°and 110°. FIG. 15F shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the optical detector (device 1) according to various embodiments as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the photocurrent at the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with incident intensity under 5.7 pm laser illumination at two selected polarization angles 9 = 70°and 160°

[0090] Furthermore, the device can be used to detect the polarization angle and wavelength simultaneously. FIG. 16A shows a plot of responsivity (in milli-Amperes per Watt or mA W" ') as a function of polarization angle 9 (in degrees or deg) illustrating the variation of responsivity of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments as a function of polarization angle for different wavelengths. FIG. 16B shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of polarization angle 0 (in degrees or deg) illustrating the variation of responsivity of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments as a function of polarization angle for different wavelengths. It may be evident from FIGS. 16A-B and FIG. 12B that the responsivity of the device may depend on the polarization angle and wavelength, but not on the incident intensity. In this context, the 2D coordinates formed by the responsivity of HJ-1 and HJ-2 for different wavelengths correspond to the polarization angles in one-to-one relation, as demonstrated in FIG. 16C. FIG. 16C shows a two dimensional plot of the responsivity of the first homojunction HJ-1 (in milli-Amperes per Watt or mA W'1) as a function of the responsivity of the second homojunction HJ-2 (in milli-Amperes per Watt or mA W'1) of the optical detector (device 1) according to various embodiments such that the polarization and wavelength can be simultaneously determined under normalization of incident intensity. Therefore, the polarization angle and wavelength of an unknown incident light witha measured intensity can be simultaneously obtained using the double twisted b-AsP homojunctions.

[0091] The incident intensity can be easily measured using a thermal detector (see FIGS. 17A - I), thus allowing the detection of an arbitrary incident light with unknown intensity, polarization angle and wavelength. FIG. 17A shows an optical microscopy image of a bismuth selenite (BizChSe) bolometric detector according to various embodiments. FIG. 17B shows a schematic illustrating the bismuth selenite (Bi2C>2Se) bolometric detector according to various embodiments under mid infrared (MIR) light illumination. FIG. 17C shows a plot of absorption (in percent or %) as a function of wavelength (in micrometers or pm) illustrating the mid infrared (MIR) absorption of three bismuth selenite (BiiChSe) according to various embodiments, with the inset showing that the MIR absorptions of the three samples are similar in the 3 pm to 6 pm range. FIG. 17D shows a plot of current (in micro- Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (Bi2C>2Se) bolometric detector according to various embodiments in the dark and under illumination of 3.7 pm laser. FIG. 17E shows a plot of current (in micro-Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (BizChSe) bolometric detector according to various embodiments in the dark and under illumination of 4.6 pm laser. FIG. 17F shows a plot of current (in micro-Amperes or pA) as a function of voltage (in volts or V) illustrating the current-voltage curves of the bismuth selenite (Bi2C>2Se) bolometric detector according to various embodiments in the dark and under illumination of 5.7 pm laser. The channel currents may show a decrease under laser illumination (compared to in the dark). Further the channel currents may decrease with the increase of incident intensity.

[0092] FIG. 17G shows a plot of current (in micro-Amperes or pA) as a function of time (in seconds or s) illustrating the time-resolved photoresponse of the bismuth selenite (Bi2O2Se) bolometric detector according to various embodiments. The channel resistance (R) shows an obvious increase when the laser is on. FIG. 17H shows a plot of resistance variation AR / R (in percent or %) as a function of polarization angle (in degrees or °) illustrating the resistance variation of the detector according to various embodiments under 3.7 pm laser illumination with different polarization angles. The resistance variation shows independence from the polarization angles, which can be attributed to the isotropic in-plane crystal structure of bismuth selenite (Bi2C>2Se). FIG. 171 shows a plot of resistance variation AR / R (in percent or%) as a function of power density (in Watts per square centimeters or W / cm2) illustrating the resistance variation of the detector according to various embodiments with incident intensity. It can be observed that the variation may not depend on the wavelength.

[0093] Note that the resistance variation is determined as AR / R = (Riight -100%, where Rdark and Riight are the channel resistance in dark and under light illumination, respectively. BizOzSe has a narrow bandgap (~0.8 eV), high carrier mobility, and low thermal conductivity, which is widely studied in electronics, optoelectronics, and thermoelectrics. Here, a thick BbChSe flake may be used as a thermal detector to detect the incident intensity of the MIR laser. Under laser illumination, the detector shows negative photoresponse, and its channel resistance increases with increasing power density, which can be explained by the bolometric effect. Namely, the thermal energy of the MIR laser is transferred to the BizOzSe when it is uniformly illuminated, which heats the BizOzSe crystal lattice and intensifies phonon-electron scattering, thereby inducing resistance increase. This resistance variation only depends on the light intensity ( ), which can be given as log(AR / R) = -1.43235 + 0.36889 x logCP). Thus, in actual use, the incident intensity can be known using the BizOzSe-based bolometric detector by measuring its resistance variation. Based on these characteristics, the intensity, wavelength, and polarization angle information of unknown incident light can all be simultaneously detected by placing a BizOzSe bolometric detector near the double twisted b- AsP homojunctions.

[0094] In addition, the repeatability of multidimensional information detection was demonstrated in other devices with thin b-AsP flakes (device 2, see FIGS. 18A - F, FIGS. 19A - D. FIGS. 20A - L, FIGS. 21A - E, FIGS. 22A-F, FIGS. 23A - F, FIGS. 24A - C) and different twist angles (device 3, see FIGS. 25A - F, FIGS. 26A - L). The low photoresponse for thin devices may be attributed to their relatively weak optical absorption, low carrier mobility, large resistance and rapid heat exchange with the substrate.

[0095] FIG. 18A shows an optical microscopy image of an optical detector (device 2) according to various embodiments. FIG. 18B shows an atomic force microscopy (AFM) image illustrating the topology of the optical detector (device 2) according to various embodiments. FIG. 18C shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 2) according to various embodiments, which indicates that the crystal orientation differences of the left black arsenic phosphorus (L-AsP) flake and the right black arsenic phosphorus (R-AsP) flake relative to the middle black arsenic phosphorus (M-AsP) flake are determined to be -45° and -135°, respectively FIG. 18D shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the left black arsenic phosphorus (L-AsP) flake of the optical detector (device 2) according to various embodiments. FIG. 18E shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the middle black arsenic phosphorus (M-AsP) flake of the optical detector (device 2) according to various embodiments. FIG. 18F shows a plot of polarization angle (in degrees or °) as a function of Raman shift (in per centimeter or cm'1) illustrating the polarized Raman intensity mapping of the right black arsenic phosphorus (R-AsP) flake of the optical detector (device 2) according to various embodiments.

[0096] FIG. 19A shows the optical microscopy image of the first homojunction HJ-1 of the optical device (device 2) according to various embodiments. FIG. 19B shows a schematic of the photocurrent mapping measured from the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments. It can be observed that the photocurrent signs at positions 1, 2, 3, and 4 arerespectively. These results may be similar to the cases shown in FIG. 9A and FIG. 9E. FIG. 19C shows a plot of the photocurrent IDS (in micro- Amperes or pA) as a function of drain-source voltage VDS (in volts or V) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments under large VDS bias voltage range (±1 V) in the dark and under 532 nm laser illumination at position 2 (laser@2) and position 3 (laser@3). It can be seen that in the large bias range of -1 to +1 V, the IDS - VDS curves present linear features. FIG. 19D shows a plot of the photocurrent IDS (in nano- Amperes or nA) as a function of drain-source voltage VDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments under VDS bias voltage range (±10 mV) in the dark and under 532 nm laser illumination at position 2 (laser@2) and position 3 (laser@3). Positive and negative photocurrents can be clearly observed for positions 2 and 3 at VDS = 0 V, respectively. The bipolar photocurrent signs at the b-AsP / b-AsP junction may result from the difference of the Seebeck coefficient.

[0097] FIG. 20A shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to variousembodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 1.9 W / cm2FIG. 20B shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 1.9 W / cm2.

[0098] FIG. 20C shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 6.7 W / cm2. FIG. 20D shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 9 (in degrees or °) at the incident intensity of 6.7 W / cm2.

[0099] FIG. 20E shows a plot of photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 11.4 W / cm2. FIG. 20F shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 11.4 W / cm2.

[0100] FIG. 20G shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 18.1 W / cm2. FIG. 20H shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 18.1 W / cm2.

[0101] FIG. 201 shows a plot of photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 23.9 W / cm2. FIG. 20J shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 23.9 W / cm2.

[0102] FIG. 20K shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 28.7 W / cm2. FIG. 20L shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 28.7 W / cm2.

[0103] FIG. 21 A shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of drain-source voltage YDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the first homojunction (HJ-1) of the optical detector (device 2) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2FIG. 21B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of drain-source voltage YDS (in milli-Volts or mV) illustrating the IDS - VDS characteristics of the second homojunction (HJ-2) of the optical detector (device 2) according to various embodiments in the dark and under 3.7 pm laser illumination with an incident intensity of 28.7 W cm'2. 0° and 90° refer to the polarization angles of the incident light. For FIGS. 21A-B, the 0 = 0° incident light is linearly polarized along the AC direction of M-AsP, while the 0 = 90° incident light is linearly polarized along the ZZ direction of M-AsP.

[0104] FIG. 21C shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2). FIG. 21D shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2). FIG. 21E shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 2) according to various embodiments under 3.7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determined. These photocurrents were measured at VDS = 0V.

[0105] FIG. 22A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 4.6 pm laser illumination at different incident intensities (4.4 W cm'2to 16.7 W cm'2). FIG. 22B shows a plot of the second photocurrent IDS.2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 4.6 pm laser illumination at different incident intensities (4.4 W cm'2to 16.7 W cm'2). These photocurrents were measured at VDS = 0V. FIG. 22C shows a two dimensional plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 2) according to various embodiments under 4.6 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 4.4 W cm'2to 16.7 W cm'2can be simultaneously determined. These photocurrents were measured at VDS = 0V.

[0106] FIG. 22D shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities (2.8 W cm'2to 34.1 W cm'2) FIG 22E shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as afunction of polarization angle 0 (in degrees or °) under 5.7 pm laser illumination at different incident intensities (2.8 W cm'2to 34.1 W cm'2). These photocurrents were measured at VDS = OV. FIG. 22F shows a two dimensional plot of the first photocurrent IDS.I (in nano- Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 2) according to various embodiments under 5.7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 2.8 W cm'2to 34.1 W cm'2can be simultaneously determined. These photocurrents were measured at VDS = 0V.

[0107] FIG. 23 A shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) of the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths. FIG. 23B shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments as a function of the power density (in Watts per square centimeter or W / cm2) illustrating the variation of photocurrent with power density at different wavelengths. The polarization angle is fixed at 0 = 0°. These photocurrents may exhibit a linear dependence on the incident intensity.

[0108] FIG. 23C shows a plot of responsivity (in milli-Amperes per Watt or mA / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation responsivity of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.

[0109] FIG. 23D shows a plot of responsivity (in milli-Amperes per W or mA / W) as a function of polarization angle 0 (in degrees or °) illustrating the variation of responsivity of the first homojunction HJ-1 of the optical detector (device 2) according to various embodiments with polarization angle for different wavelengths. FIG. 23E shows a plot of responsivity (in milli-Amperes per W or mA / W) as a function of polarization angle 0 (in degrees or °) illustrating the variation of responsivity of the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with polarization angle for different wavelengths. FIG. 23F shows a two dimensional plot of the responsivity of the first homojunction HJ-1 (in milli-Amperes per Watt or mA / W) as a function of the responsivity of the second homojunction HJ-2 (in milli-Amperes per Watt or mA / W) of the optical detector (device 2) according to various embodiments such that the polarization and wavelength can be simultaneously determined under normalization of incident intensity.

[0110] FIG. 24 A shows a plot of noise current (in square Amperes per Hertz or A2 / Hz) as a function of frequency (in Hertz or Hz) illustrating variation of noise currents of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with frequency FIG 24B shows a plot of noise equivalent power NEP (in pico-Watts per square-root Hertz or pW / Hz05) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the NEP of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°. FIG. 24C shows a plot of detectivity (xlO8centimeter square-root Hertz per Watt or cm Hz05 / W) as a function of power density (in Watts per square centimeter or W / cm2) illustrating the variation of the detectivity of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 2) according to various embodiments with incident intensity for different wavelengths at polarization angle 0 = 0°.

[0111] FIG. 25A shows an optical microscopy image of an optical detector (device 3) according to various embodiments. The thickness of as-used b-AsP flakes is about 60 nm. FIG. 25B shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 3) according to various embodiments, which makes it possible to determine the crystal orientation of the b-AsP flake via Ag2 / Ag1(armchair or AC) > Ag2 / A (zig-zag or ZZ). FIG. 25C shows a schematic illustrating that the crystal orientation differences of the left black arsenic phosphorus (L-AsP) flake and the right black arsenic phosphorus (R-AsP) flake relative to the middle black arsenic phosphorus (M-AsP) flake are determined to be -60° and -120°, respectively.

[0112] FIG. 25D shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2). FIG. 25E shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) exhibited by the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) under 3.7 pm laser illumination at different incident intensities (1.9 W cm'2to 28.7 W cm'2). FIG. 25F shows a two dimensional plot of the first photocurrent 1DS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2(in nano- Amperes or nA) of the optical detector (device 3) according to various embodiments under 3 7 pm laser illumination such that the polarization angle from 0° to 180° and incident intensity from 1.9 W cm'2to 28.7 W cm'2can be simultaneously determined. These photocurrents were measured at VDS = 0V.

[0113] FIG. 26A shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity ( ) of 1.9 W / cm2. FIG. 26B shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 1.9 W / cm2.

[0114] FIG. 26C shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 6.7 W / cm2. FIG. 26D shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 6.7 W / cm2.

[0115] FIG. 26E shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 11.4 W / cm2. FIG. 26F shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 0 (in degrees or °) at the incident intensity of 11.4 W / cm2.

[0116] FIG. 26G shows a plot of photocurrents fos.i IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 6 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 18.1 W / cm2. FIG. 26H shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 9 (in degrees or °) at the incident intensity of 18.1 W / cm2.

[0117] FIG. 261 shows a plot of photocurrents IDS I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 0 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 23.9 W / cm2. FIG. 26J shows a plot of the photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 9 (in degrees or deg) at the incident intensity of 23.9 W / cm2.

[0118] FIG. 26K shows a plot of photocurrents IDS.I IDS, 2 (in nano-Amperes or nA) as a function of time (in seconds or s) illustrating photoswitching response of the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments when the polarization angle 9 is rotated from 0° to 180° with a step of 10° at VDS = 0 V and under 3.7 pm laser illumination with an incident intensity (P) of 28.7 W / cm2. FIG. 26L shows a plot of the photocurrents IDS,I IDS, 2 (in nano-Amperes or nA) exhibited by the first homojunction HJ-1 and the second homojunction HJ-2 of the optical detector (device 3) according to various embodiments as a function of polarization angle 9 (in degrees or deg) at the incident intensity of 28.7 W / cm2.

[0119] Next, an electrical-tuning approach to improving the polarization photoresponse may be demonstrated, which may be useful for more accurate discrimination of polarization angles with a low incident intensity As shown in FIGS. 8E-F, the optical detector may exhibit a better conductivity at a more negative gate voltage (PGS), indicating that higher hole concentrations are achieved. Under 3.7 pm laser illumination with an intensity of 1.9 W cm-2and VDS = 0 V, an enhanced photoresponse may be observed in both HJ-1 and HJ-2 at a more negative VGS, as presented in FIGS. 27A-B. FIG. 27A shows a plot of polarization angle 0 (in degrees or °) as a function of gate voltage VGS (in volts or V) illustrating the photocurrent map of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with 0 and VGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V. FIG. 27B shows a plot of polarization angle 0 (in degrees or °) as a function of gate voltage VGS (in volts or V) illustrating the photocurrent map of the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments with 0 and VGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V. The gate-dependent photocurrent of HJ-1 at polarization angles of 0° and 90° shows a nearly fourfold enhancement of photocurrent at FGS = -40 V compared with that at VGS= 0 V. Such enhancement may be attributed to the increase in hole carrier concentration at more negative gate voltages. The electrical-tuning approach to improving the polarization photoresponse may be better demonstrated by extracting the polarization-dependent photocurrents of HJ-1 and HJ-2 at different gate voltages.

[0120] FIG. 27C shows a two dimensional plot of the first photocurrent IDS.I (in nanoAmperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 1) according to various embodiments at different polarization angles (0 = 0 - 180°) and gate voltage (VGS = 0, -20 and -40 V), demonstrating the electrically tunable polarization response characteristics. As can be seen in FIG. 27C, the photocurrent difference between adjacent polarization angles may become larger under a larger negative value of VGS, which may be favourable for distinguishing polarization angles more accurately. Moreover, the responsivity of the device may be improved to be ~ 150 mAW"1, indicating that the device can simultaneously detect the polarization angle and wavelength with a better accuracy, which may provide new approaches for designing miniaturized spectropolarimetry. FIG. 27D shows a plot of responsivity (in milli-Amperes per Watt or mA W'1) as a function of gate voltage VGS (in Volts or V) illustrating variation of responsivity of the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments with gate voltage at polarization angles 0 = 20° and 0 = 110°. FIG. 27D shows that the responsivity of the device may be improved to — 150 mAW-1at VGS= ~40 'V, indicating that the device can simultaneously detect the polarization angle and wavelength with better accuracy.

[0121] FIGS. 28A-F, FIG. 29A-F and FIGS. 30 A- C show the repeatability of electricaltuning polarization detection in a thin device (device 4).

[0122] FIG. 28 A shows an optical microscopy image of an optical detector (device 4) according to various embodiments FIG. 28B shows a polar plot of the extracted angle-resolved Raman intensity ratio of the Ag2 / Ag1mode of the three black arsenic phosphorous (b-AsP) flakes of the optical detector (device 4) according to various embodiments. FIG. 28C shows a plot of the first photocurrent IDS,I (in nano- Amperes or nA) as a function of drain-source bias VDS (in milli-Volts or mV) illustrating the output characteristics curves of the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments. FIG. 28D shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of drain-source bias VDS (in milli-Volts or mV) illustrating the output characteristics curves of the second homojunction HJ-2 of the optical detector (device 4) according to various embodiments. FIG. 28E shows a plot of the photocurrent IDS (in nano-Amperes or nA) / gate current IGS (in nano-Amperes or nA) as a function of gate voltage FGS (in Volts or V) illustrating the characteristic curves of the optical detector (device 4) according to various embodiments at drain-source bias VDS = 10 mV. FIG. 28F shows a plot of the photocurrent IDS (in nano- Amperes or nA) as a function of gate voltage FGS (in Volts or V) illustrating the characteristic curves of the optical detector (device 4) according to various embodiments at drain-source bias VDS = 0 V.

[0123] FIG. 29A shows a plot of polarization angle 0 (in degrees or °) as a function of gate voltage FGS (in volts or V) illustrating the photocurrent map of the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments with 0 and FGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V. FIG. 29B shows a plot of polarization angle 0 (in degrees or °) as a function of gate voltage G (in volts or V) illustrating the photocurrent map of the second homojunction HJ-2 of the optical detector (device 4) according to various embodiments with 0 and FGS under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at drain-source bias VDS = 0 V. FIG. 29C shows a plot of the first photocurrent IDS.I (in nano-Amperes or nA) as a function of the gate voltage FGS (in Volts or V) illustrating the variation of the photocurrent at the first homojunction HJ-1 of the optical detector (device 4) according to various embodiments at polarization angles 0 = 0° and 0 = 90° (3.7 pm laser illumination with an incident intensity of 1.9 W cm'2), which increases with more negative gate voltage. FIG. 29D shows a plot of thefirst photocurrent IDS.I (in nano- Amperes or nA) as a function of polarization angle 9 (in degrees or °) illustrating the variation of the photocurrent at the first homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 1 .9 W cm'2with polarization angles at KGS = 0 V, -20 V and -40 V. FIG. 29E shows a plot of the second photocurrent IDS, 2 (in nano-Amperes or nA) as a function of polarization angle 9 (in degrees or °) illustrating the variation of the photocurrent at the second homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2with polarization angles at GS = 0 V, -20 V and -40 V. The drain-source bias VDS is at 0V. FIG. 29F shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 1.9 W cm'2at different polarization angles (9 = 0 - 180°) and gate voltages (KGS = 0 V, -20 V and -40 V), demonstrating the electrically tunable polarization response characteristics.

[0124] The practicability of the electrical -tuning approach may further demonstrated be for a lower incident intensity of 0.15 W cm-2, which is close to the solar constant on Earth (FIGS. 30A - C). FIG. 30A shows a plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of polarization angle 0 (in degrees or °) illustrating the variation of the photocurrent at the first homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0.15 W cm'2with polarization angle at KGS = 0 V and -40 V. FIG. 30B shows a plot of the second photocurrent IDS, 2 (in nano- Amperes or nA) as a function of polarization angle 9 (in degrees or °) illustrating the variation of the photocurrent at the second homojunction of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0. 15 W cm'2with polarization angle at KGS = 0 V and -40V The drain-source bias VDS is at 0V FIG. 30C shows a two dimensional plot of the first photocurrent IDS,I (in nano-Amperes or nA) as a function of the second photocurrent IDS, 2 (in nano-Amperes or nA) of the optical detector (device 4) according to various embodiments under 3.7 pm laser illumination with an incident intensity of 0.15 W cm'2at different polarization angles (9 = 0 - 180°) and gate voltages (KGS= 0 V and -40 V), demonstrating more accurate discrimination of polarization angles with a low incident intensity by applying a more negative gate voltage.

[0125] Additionally, the practical usage of the double twisted b-AsP homojunctions for simultaneously detecting polarization angle and incident intensity in an imaging application to obtain multidimensional information may be demonstrated. A simple imaging set-up may be established for such a demonstration. FIG 31 A is a schematic illustrating a simple imaging set-up and data-processing method for image reconstruction according to various embodiments. A metal mask with cut-out letters ‘N’, ‘T’ and ‘U’ is used to create three MIR objects with different radiation intensities and polarization angles. An MIR laser source with a wavelength of 5.7 pm is directed onto the device through the metal mask, which can move in the x and y directions. The radiation intensity of the ‘N’, ‘T’ and ‘U’ was set to 2.8 W cm-2, 14.4 W cm2and 34.1 W cm2, and the corresponding polarization angle was set to 45°, 90° and 135°, respectively. Based on the measured photocurrents (TDS,I and IDS, 2) of HJ-1 and HJ- 2 at VDS = 0 V, the intensity and polarization angle can be simultaneously obtained by following the data-processing method described below.

[0126] As mentioned above (FIG. 11B and FIG. 12A), the photocurrents of both HJ-1 and HJ-2 may show a linear dependence on the incident intensity (IDS = RXF>). Thus, the photocurrents measured at different intensities and polarization angles can be fitted with the following equations:(2)where 1DS,I and IDS, 2 are the measured photocurrent of HJ-1 and HJ-2 under MIR illumination, and Ri and R2 are the responsivity of HJ-1 and HJ-2, respectively. P is the incident intensity. A, B, C and D in Equations (1) - (2) are constants that can be obtained by fitting the polarization-angle-dependent responsivity The values of A, B, C and D were fitted to be 21.1 1 , 1.11, 15.56 and 2.22, respectively, under a 5.7 pm laser illumination.

[0127] The measured photocurrents of HJ-1 and HJ-2 are presented in FIGS. 31B - C, respectively, in which the letters ‘N’, ‘T’ and ‘U’ are clearly distinguishable. FIG. 3 IB shows the measured photocurrent for the first homojunction HJ-1 of the optical detector (device 1) according to various embodiments. FIG. 31C shows the measured photocurrent for the second homojunction HJ-2 of the optical detector (device 1) according to various embodiments.

[0128] Based on the data-processing method described above, the intensities and polarization angles of the ‘N’, ‘T’ and ‘U’ objects are simultaneously obtained, as shown in FIGS. 3 ID - E. FIG. 3 ID shows the reconstructed intensity information of the ‘N’, ‘T’ and ‘LFtargets obtained using the data-processing method according to various embodiments. FIG. 3 IE shows the reconstructed polarization angle information of the ‘N’, ‘T’ and ‘U’ targets obtained using the data-processing method according to various embodiments. The reconstructed multidimensional information may exhibit a clear contrast and good agreement with the preset conditions.

[0129] FIG. 32A shows a plot of intensity P (in Watts per square centimeters or W / cm2) as a function of position comparing the reconstructed intensity information with pre-set intensity data (denoted by horizontal dashed lines) according to various embodiments. FIG. 32B shows a plot of polarization angle 0 (in degrees or °) as a function of position comparing the reconstructed polarization angle information with pre-set polarization angle data (denoted by horizontal dashed lines) according to various embodiments.

[0130] The reconstructed intensities and polarization angles may be in perfect agreement with the pre-set experimental conditions, indicating the promising potential of the device for multidimensional optical information imaging applications.

[0131] Various embodiments may relate to a multidimensional optical information detection device based on double twisted b-AsP homojunction, as well as a method of forming the same. Specifically, the polarization angle and incident density of an MIR light can be directly and simultaneously detected by measuring the photocurrents of the double twisted b- AsP homojunctions, and the wavelength information can also be obtained by extracting the responsivity of the homojunctions. Various embodiments may feature a zero-bias work mechanism based on the photothermoelectric effect with room temperature operation and bipolar polarization photoresponse, which may be highly desired for next-generation detectors with low power consumption, uncooled operation and diverse functions. A MIR detector may be developed as a demonstration example, as described herein. Moreover, the polarization photoresponse performance can be tuned using a gate electric field, enabling more accurate discrimination of polarization angles under a low incident intensity. With these features, various embodiments may potentially be used in emerging infrared technologies such as polarimetric imaging, environmental monitoring and free-space communications.

[0132] Anisotropic Raman and MIR optical absorption characterizations of the double twisted b-AsP homojunctions

[0133] The b-AsP features an in-plane anisotropic crystal structure, as shown in FIG. 5B. In view of this characteristic, the b-AsP flakes may be prepared using an oriented mechanicalexfoliation method. Specifically, the crystal orientation of a b-AsP bulk crystal may be determined using polarized Raman spectroscopy. The bulk crystal may be repeatedly exfoliated along the same crystal orientation. Subsequently, the as-exfoliated b-AsP flakes with a certain crystal orientation may be transferred onto SiOz / Si substrates using polydimethyl siloxane (PDMS) in accordance with the desired twist angles. Finally, the crystal orientations of the three b-AsP layers may be further confirmed by using polarized Raman spectroscopy. The intensity ratio of Ag2 / Ag' can be used to determine the armchair (AC) and zigzag (ZZ) crystal orientation as Ag2 / Agx(AC) > Ag2 / AgL(ZZ).

[0134] Anisotropic mid-infrared reflection and transmission spectra of b-AsP flakes may be collected using a Bruker FTIR spectrometer (Vertex 80v) equipped with a Hyperion 2000 microscope and a broadband polarizer A fresh CaFz substrate with high transmittance in the mid-infrared spectrum range may be used to support the exfoliated b-AsP flakes for the measurement. In addition, the armchair (AC) and zigzag (ZZ) crystal orientation of the b-AsP flake may be determined by polarized Raman spectroscopy before performing anisotropic optical characterization. The optical absorption spectra may be obtained by 1 -transmissionreflection. As shown in FIG 7D, the calculated absorption may show an obvious anisotropy, in which the maximum is along the AC orientation. In addition, the optical absorption is stronger in a thick b-AsP flake (~126 nm) than that in a thin one (~52 nm), which could result in a higher photoresponse.

[0135] Photoresponse mechanism of the double twisted b-AsP homojunctions

[0136] The photocurrent mappings shown in FIG. 9A and FIG. 19B may be obtained using a 532 nm laser with an incident intensity of ~10 pW. The laser spot is about ~1 pm. The devices were operated at zero bias (VDS = 0 V). As can be seen, the photocurrents are not only generated from the b-AsP / metal contact interfaces but also extend to regions far away from the contact. In addition, both positive and negative photocurrents were observed in the b-AsP / b-AsP junction. Photocurrent generation mechanisms are usually categorized as photoconduction effect, photogating effect, photovoltaic (PV) effect, photothermoelectric (PTE) effect, and bolometric effect. The photoconduction, photogating, and bolometric effects are usually observed under external bias, while the PV and PTE effects may usually dominate at zero bias. The photocurrent mappings and polarization-dependent MIR photoresponse may be measured at zero bias. Thus, the photocurrent generation in the devices may be attributed to the PV or PTE effect. The PV effect may rely on a built-in potential that exists in a P-N junction orsemiconductor-metal junction with a non-negligible Schottky barrier. In this case, the photocurrent sign may be unipolar due to the fixed built-in electric field direction at the junction. However, bipolar photocurrent signs were observed at the b-AsP / b-AsP junctions. Therefore, the PV effect may not dominate the photoresponse in the devices.

[0137] Device 1 with -120 nm b-AsP flakes show linear IDS-VDS characteristics in a large bias voltage range (± 1 V) (FIGS. 8C - D) and exhibits high carrier mobility up to 620 cm2 / (V s). The linear IDS-VDS characteristics are also observed in device 2 with -55 nm b-AsP flakes (FIG. 19C). These results may indicate negligible Schottky barriers between b-AsP and Au metal electrodes. In addition, the barrier height of b-AsP / Au was evaluated to be 35 meV previously. Based on this, it may be believed that the PV effect induced by the Schottky barrier may be negligible.

[0138] In order to better understand the photoresponse mechanism in the devices, the photocurrent generation through a band diagram may be quantitatively described in a band diagram (FIGS. 9C - E). The b-AsP is a p-doping semiconductor, and the overlapping region of L-AsP and M-AsP can be considered p“-doping due to its thicker thickness. Thus, the HJ-2 can be described as an Au / p / p+ / p / Au junction. Assuming that the PV effect dominates the photocurrent generation of HJ-2, the photocurrent sign at positions 1, 2, 3, and 4 in HJ-2 should berespectively. However, the measured photocurrents do not agree with the PV effect description, indicating that the PV effect cannot be considered as the dominant response mechanism of the device.

[0139] After excluding the PV effect, the PTE effect may be assumed to dominate the photoresponse mechanism of the device, as shown in FIG. 9E. At position 1, local heating by laser illumination may cause the increase of carrier (hole) concentrations and may induce a temperature gradient from drain to source, which drives the hot carriers to diffuse from drain to source, thereby forming negative photocurrents When laser heating position 2 or 3, the overlapping region could exhibit a higher temperature and the hot carriers (holes) could diffuse out of there. As the Seebeck coefficient of the p+-doping region is lower than that of the p- doping region, the holes (or electrons) may be driven by the differences of the Seebeck coefficient and behave to flow “downhill” (or “uphill”). So, for position 2, holes (or electrons) move from source to drain (or from drain to source), resulting in positive photocurrents. In contrast, negative photocurrents may be generated at position 3. The photocurrent generationat position 4 is contrary to position 1. These analyses based on the PTE effect can be well agreed with the experimental results shown in FIG 9A and FIG. 19B

[0140] As such, it may be believed that the photocurrent generation in the b-AsP homojunctions is mainly attributed to the PTE effect. Similar phenomena were observed in a double gated semiconducting nanotube and vertical black phosphorus p-n junction. The photocurrents at b-AsP / Au interfaces may be larger than those at overlapping regions. This could originate from the following two enhancements. One is that the surface plasmon resonance of Au electrodes may enhance hot carrier injection. The other is that the reflection of the Au electrodes on the incident light may further increase the light absorption of the b- AsP, resulting in larger photocurrents.

[0141] Photoresnonse performance of the double twisted b-AsP homojunctions

[0142] Photoresponse performance in terms of responsivity (R) and detectivity (D*) are extracted using the following formula:wherein Ipu, P, A, B, and NEP are photocurrent, incident intensity, device area, measuring bandwidth, and noise equivalent power, respectively.

[0143] The photoresponse of the devices may be measured at zero bias. The dark currents (Idark) of the devices may be much lower than the photogenerated drain-source currents (IDS). Thus, the photocurrents (IPH = IDS - Idark) can be replaced by the directly measured IDS at VDS = 0 V. The device area of HJ-1 and HJ-2 is about 105 pm2in device 1. In device 2, the device area of HJ-1 and HJ-2 is about 120 pm2. The thickness of b-AsP flakes used in device 1 and device 2 is about 120 nm and 55 nm, respectively. NEP can be calculated using NEP = A / R, where A is noise current. According to these formulas, the as-extracted responsivity, NEP, and detectivity of device 1 and device 2 are shown in FIGS. 12A - G, and FIGS. 23A - F, FIGS. 24A - C, respectively. For device 1 , the responsivity, NEP, and detectivity are calculated to be -45.6 mA / W, -0.9 pW / Hz05, and -1.2 x 109cm Hz05 / W for 3.7 pm, respectively. In addition, the detectivity of device 1 for 4.6 pm and 5.7 pm reached up to -7 x 108cm Hz05AV and -4 x 108cm-Hz05 / W, respectively. For device 2, the photoresponse performance shows a decrease, which may be attributed to their weak optical absorptions, low carrier mobilities, large resistances, and rapid heat exchange with the substrate.

[0144] The response time of device 1 is evaluated to be -21 / 17 ps, as shown in FIGS. 13A - B, which may be comparable to the reported black phosphorus homojunction photodetector dominated by the PTE effect. Such fast response speed may be attributed to the high carrier mobility of b-AsP In general, the response time may mainly be determined by the transport time (T) of carriers in the channel, which can be evaluated using the following simple model:where L is the channel length, p is the carrier mobility and VDS is the applied bias. As shown in FIG. 8E, the carrier mobility is calculated to be 620 cm2 / (V s) at VDS = 10 mV. The channel length is about 10 pm. Therefore, the evaluated intrinsic transport time is about 0.16 ps, indicating that the response time on the order of microseconds may be reasonable in the device.

[0145] Reconstruction of polarization angle and intensity information using the double twisted b-AsP homoi unctions

[0146] The relationship between responsivity (R) of HI-1 and HJ-2 and polarization angle (0) can be described by Equations (1) and (2) above. A, B, C and D are constants which can be obtained by fitting the polarization angle-dependent responsivity, which are listed in FIG. 33. FIG. 33 shows a table providing the value of constants A, B, C, D for different wavelengths according to various embodiments. By combining Equations (1) and (2), the following equations may be obtained:

[0148] Based on Equation (1), the polarization angle 0 can be obtained as follows: a 0 = t ian n 0 — 4 t.an

[0149] Two 0 values may be obtained, but only one of the two values may be the correct polarization angle. To get this correct polarization angle, these two values may be plugged intoEquations (1) or (2) and solve for the power value. According to calculations, the solved power values may be a positive value and a negative value. The positive intensity value (P) corresponds to the correct polarization angle (0). Based on these, the correct intensity value (P) and polarization angle (0) are simultaneously obtained. Note that arc tangent function has a value range of -90° to 90°, while the polarization angle range detected is [0-180°]. Therefore, the correct polarization angle should be 0 + 180° when 0 < 0°.

Claims

Claims1. An optical detector comprising: a first photosensitive element comprising a two-dimensional material; a second photosensitive element comprising the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element; and a third photosensitive element comprising the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element; wherein an armchair (AC) orientation of the first photosensitive element is along a first direction; wherein an armchair orientation (AC) of the second photosensitive element is along a second direction different from the first direction; and wherein an armchair orientation of the third photosensitive element is along a third direction different from the first direction and different from the second direction.

2. The optical detector according to claim 1, wherein the second direction is at an angle of a! degrees relative to the first direction; and wherein the third direction is at an angle of a2 degrees relative to the first direction, a2 degrees being equal to 180 degrees subtracted by al degrees.

3. The optical detector according to claim 1 or claim 2, wherein a thickness of the first photosensitive element, a thickness of the second photosensitive element and a thickness of the third photosensitive element are substantially equal.

4. The optical detector according to any one of claims 1 to 3,wherein a size of the first photosensitive element, a size of the second photosensitive element and a size of the third photosensitive element are substantially equal.

5. The optical detector according to one of claims 1 to 4, wherein the two-dimensional material is any one selected from a group consisting of black arsenic-phosphorous (bAsP), black phosphorous (bP), palladium selenide (PdSe ), tantalum iridium telluride (TalrTer), tellurium (Te) and tantalum nickel selenide (TazNiSes).

6. The optical detector according to any one of claims 1 to 5; wherein each of the first photosensitive element, the second photosensitive element and the third photosensitive element is a flake comprising one or more monolayers.

7. The optical detector according to any one of claims 1 to 6, further comprising: a substrate; and an insulating layer on the substrate such that the first photosensitive element, the second photosensitive element and the third photosensitive element are on the insulating layer.

8. The optical detector according to any one of claims 1 to 7, further comprising: a first electrode in contact with the first photosensitive element, a second electrode in contact with the second photosensitive element; and a third electrode in contact with the third photosensitive element.

9. The optical detector according to any one of claims 1 to 8, wherein the optical detector is configured to determine a polarization angle and an intensity of a light incident onto the optical detector by measuring a firstphotocurrent flowing through the first homojunction and a second photocurrent flowing through the second homojunction.

10. The optical detector according to claim 9, wherein the optical detector is configured to determine the polarization angle and a wavelength of the light incident onto the optical detector by determining a first responsivity of the first homojunction and a second responsivity of the second homojunction.

11. The optical detector according to any one of claims 1 to 10, wherein the optical detector comprises a first source and a first drain associated with the first homojunction, the first source and the first drain configured to be biased with a first potential difference between the first source and the first drain; and wherein the optical detector comprises a second source and a second drain associated with the second homojunction, the second source and the second drain configured to be biased with a second potential difference between the second source and the second drain.

12. A method of forming an optical detector, the method comprising: forming a first photosensitive element comprising a two-dimensional material; forming a second photosensitive element comprising the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element; and forming a third photosensitive element comprising the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element; wherein an armchair (AC) orientation of the first photosensitive element is along a first direction;wherein an armchair orientation (AC) of the second photosensitive element is along a second direction different from the first direction; and wherein an armchair orientation of the third photosensitive element is along a third direction different from the first direction and different from the second direction.

13. The method according to claim 12, wherein the second direction is at an angle of al degrees relative to the first direction; and wherein the third direction is at an angle of a2 degrees relative to the first direction, a2 degrees being equal to 180 degrees subtracted by al degrees.

14. The method according to claim 12 or claim 13, wherein a thickness of the first photosensitive element, a thickness of the second photosensitive element and a thickness of the third photosensitive element are substantially equal.

15. The method according to any one of claims 12 to 14, wherein a size of the first photosensitive element, a size of the second photosensitive element and a size of the third photosensitive element are substantially equal.

16. The method according to one of claims 12 to 15, wherein the two-dimensional material is any one selected from a group consisting of black arsenic-phosphorous (bAsP), black phosphorous (bP), palladium selenide (PdSe2), tantalum iridium telluride (TaIrTe4), tellurium (Te) and tantalum nickel selenide (TazNiSe )17. The method according to any one of claims 12 to 16, wherein each of the first photosensitive element, the second photosensitive element and the third photosensitive element is a flake comprising one or more monolayers18. The method according to any one of claims 12 to 17, the method further comprising: forming an insulating layer on a substrate; and forming the first photosensitive element, the second photosensitive element and the third photosensitive element on the insulating layer.

19. The method according to any one of claims 12 to 18, further comprising: forming a first electrode in contact with the first photosensitive element, forming a second electrode in contact with the second photosensitive element; and forming a third electrode in contact with the third photosensitive element.

20. The method according to any one of claims 12 to 19, wherein the optical detector is configured to determine a polarization angle and an intensity of a light incident onto the optical detector by measuring a first photocurrent flowing through the first homojunction and a second photocurrent flowing through the second homojunction.

21. The method according to claim 20, wherein the optical detector is configured to determine the polarization angle and a wavelength of the light incident onto the optical detector by determining a first responsivity of the first homojunction and a second responsivity of the second homojunction.

22. The method according to any one of claims 12 to 21,wherein the optical detector comprises a first source and a first drain associated with the first homojunction, the first source and the first drain configured to be biased with a first potential difference between the first source and the first drain; and wherein the optical detector comprises a second source and a second drain associated with the second homojunction, the second source and the second drain configured to be biased with a second potential difference between the second source and the second drain.

23. A method of operating an optical detector, the method comprising: providing a light to the optical detector, the optical detector comprising: a first photosensitive element comprising a two-dimensional material; a second photosensitive element comprising the two-dimensional material, the second photosensitive element forming a first homojunction with the first photosensitive element; and a third photosensitive element comprising the two-dimensional material, the third photosensitive element forming a second homojunction with the first photosensitive element; determining a first photocurrent flowing through the first homojunction; and determining a second photocurrent flowing through the second homojunction; wherein an armchair (AC) orientation of the first photosensitive element is along a first direction; wherein an armchair orientation (AC) of the second photosensitive element is along a second direction different from the first direction; and wherein an armchair orientation of the third photosensitive element is along a third direction different from the first direction and different from the second direction.

24. The method according to claim 23,wherein the optical detector is configured to determine a polarization angle and an intensity of the light incident onto the optical detector based on the first photocurrent and the second photocurrent.

25. The method according to claim 24, further comprising: determining a first responsivity of the first homojunction based on the first photocurrent; and determining a second responsivity of the second homojunction based on the second photocurrent; wherein the optical detector is configured to determine the polarization angle and a wavelength of the light incident onto the optical detector based on the first responsivity and the second responsivity.

26. The method according to any one of claims 23 to 25, further comprising: applying a first potential difference between a first source and a first drain associated with the first homojunction before determining the first photocurrent flowing through the first homojunction; and applying a second potential difference between a second source and a second drain associated with the second homojunction before determining the second photocurrent flowing through the second homojunction.

27. The method according to any one of claims 23 to 26, further comprising: applying a biasing gate voltage to a substrate; wherein the substrate is separated or spaced apart from the first photosensitive element, the second photosensitive element and the third photosensitive element by an insulating layer.

Images