Photodetectors comprising black silicon

Abstract

The present invention relates to a photodetector comprising black silicon, wherein the black silicon is silicon treated with a first etching gas comprising Cl2, and a second etching gas comprising at least one of SF6, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCl3. The present invention also relates to a method of preparing black silicon, comprising: (i) pre-treating a silicon surface with a first etching gas comprising Cl2; and (ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SF6, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCl3 thereby forming black silicon. The present invention further relates to a method of preparing a photodetector, comprising: (i) pre-treating a silicon surface with a first etching gas comprising Cl2; (ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SF6, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCl3 to form black silicon; (iii) applying graphene on the black silicon.

Description

[0001] Photodetectors Comprising Black Silicon

[0002] Technical Field

[0003] The present disclosure generally relates to optoelectronic devices, and more particularly relates to photodetectors comprising black silicon.

[0004] Background Art

[0005] Research on high-efficiency and low-power optoelectronic devices is necessary to combat global climate change and constantly increasing energy consumption. Silicon (Si) has been widely used in microelectronics and optoelectronics due to its abundance, cost-effectiveness, and decent device performance. Tn the photovoltaic field. Si solar cells have been the driving force by accounting for more than 90% of the current photovoltaic market among different types of solar cells made on copper indium gallium selenide (CIGS), perovskite, and gallium arsenide (GaAs).

[0006] To improve device performance, various techniques have been shown, such as texturing, passivation, structural design, and optimization. Black silicon (or black Si) refers to Si composed of nano- or micro-structured surface and has drawn interest for its excellent light absorption properties with a low reflectance of - 1 %, compared to planar Si shows a reflectance above 30% across the 300 to 1200 nm wavelength range. These outstanding optical properties of black Si make it widely applicable in optical and electrical devices such as solar cells, photodetectors, lithium-ion batteries, micro-electro-mechanical systems (MEMS), water splitting, drug delivery, and chemical and biological sensors. However, despite the intensive research conducted on black Si, it still suffers from high carrier recombination rate and surface damage caused by the nanotexturing process, leading to limited device performance.

[0007] Conventional black Si devices involve intricate process steps for nanotexturing (e.g., metal- assisted chemical etching, reactive ion etching (RTE)), as well as surface passivation via thin film deposition to ensure high passivation quality and optimal device performance. However, the application of thin film-based passivation techniques is inefficient for Schottky junction devices as it impedes the formation of direct contact between the metal and semiconductor, which is necessary to achieve a high built-in potential.

[0008] In the field of optoelectronics, there has been significant recent interest in self-powered Schottky photodetectors based on 2D / 3D heterojunctions due to their low energy consumption and high responsivity. However, there has been limited research on self-powered black Si Schottky photodetectors. This limitation can be attributed to the high surface recombination of black Si, which hinders the generation of a strong electric field necessary for self-powered operation.

[0009] Thus, there is a need to provide photodetectors that overcome, or at least ameliorate one or more of the disadvantages described above.

[0010] Summary

[0011] In one aspect of the present disclosure, there is provided a photodetector comprising black silicon, wherein the black silicon is silicon treated with a first etching gas comprising chlorine (Cb), and a second etching gas comprising at least one of sulfur hexafluoride (SFe), tetrafluoromethane (CF4), trifluoromethane (CHF3), tetrafluoroammonium (NF4), hydrogen bromide (HBr), hydrogen (H2), oxygen (O2), fluorine (F2), or boron trichloride (BCE). In another aspect of the present disclosure, there is provided a method of preparing black silicon, comprising:

[0012] (i) pre-treating a silicon surface with a first etching gas comprising Cb; and

[0013] (ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCh thereby forming black silicon.

[0014] In a further aspect of the present disclosure, there is provided a method of preparing a photodetector, comprising:

[0015] (i) pre-treating a silicon surface with a first etching gas comprising Cb;

[0016] (ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCb to form black silicon;

[0017] (iii) applying graphene on the black silicon.

[0018] In another aspect of the present disclosure, there is provided black silicon produced by the methods disclosed herein.

[0019] Advantageously, the photodetectors disclosed herein may exhibit increased effective lifetime, reduced normalized defect density, and an increased Schottky barrier height.

[0020] Further advantageously, the photodetectors disclosed herein may exhibit superior optoelectronic properties such as responsivity, efficiency, short circuit current density (Jsc), and open-circuit voltage (Voc).

[0021] Also advantageously, the photodetectors disclosed herein may be self-powered, which may allow them to function without an external power supply.

[0022] Definitions

[0023] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, are those well- known and commonly used in the art.

[0024] Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.

[0025] As used herein, the term “black silicon’' refers to a type of silicon material that has been engineered to have a nanostructured or microstructured surface. This is typically achieved by creating microscopic or nanoscopic textures on the surface of silicon, either through chemical etching, laser treatment, or other processes.

[0026] The word “substantially’' does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

[0027] As used herein in the specification and in the claims, the phrase "at least," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a nonlimiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and / or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0028] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

[0029] As used herein, the term "about", in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0030] Throughout this disclosure, certain embodiments may be disclosed in a range format, it should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0031] Brief Description of Drawings

[0032] The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0033] Fig. 1

[0034] Fig. 1 is a schematic diagram illustrating a method of preparing a photodetector of the present invention.

[0035] Fig- 2

[0036] Fig. 2 (a) and (b) show cross-sectional scanning electron microscope (SEM) images of a comparative embodiment (reactive ion-etched (RIE) black Si using SFe without pre-treatment with Clz), (c) and (d) show SEM images of an embodiment of the present invention (RIE etched black Si using CI2 and SFe), (e) is a graph depicting the reflectance of said comparative embodiment and embodiment of the present invention, as well as other comparative embodiments (planar Si and RIE etched Si using only CI2) as a function of wavelength, and (f) is a perspective view of a photodetector of the present invention and its components, its inset showing a zoomed in SEM image of the black Si surface.

[0037] Fig. 3

[0038] Fig. 3 is a series of cross-sectional SEM images, with (a) showing a comparative embodiment (RTE etched black Si using SFe without pre-treatment with CI2), (b) showing an embodiment of the present invention (RIE etched black Si using Ch and SFe), (c) showing a comparative embodiment (and RIE etched Si using only Ch).

[0039] Fig. 4

[0040] Fig. 4 is a scries of graphs, with (a) showing the effective lifetime of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RIE etched Si using only SFe, and RIE etched Si using only Ch) as a function of injection level, (b) showing the effective lifetime of said embodiments at one sun intensity, and (c) showing the normalized defect density for said embodiments.

[0041] Fig. 5

[0042] Fig. 5 is a series of X-ray photoelectron spectra of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RTE etched Si using only SFe, and RIE etched Si using only Ch) with (a) showing the Si 2p spectra, (b) showing the O Is spectra, (c) showing the F Is spectra, and (d) showing the Cl 2p spectra.

[0043] Fig. 6

[0044] Fig. 6 is a series of diagrams illustrating the nanotexturing of an embodiment of the present invention (RIE etched black Si using Ch and SFe), with (a) showing the surface morphology of the embodiment, and (b) showing the mechanism of passivation via Ch.

[0045] Fig. 7

[0046] Fig. 7 is a series of graphs showing the (a) responsivity, and (b) external and internal quantum efficiency of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, and RIE etched Si using only SFe).

[0047] Fig. 8

[0048] Fig. 8 is a series of graphs showing the (a) dark and photocurrent density -voltage curves, (b) specific detectivity, (c) normalized photo to dark current ratio (NPDR), (d) photocurrent density and responsivity, (e) transient photocurrent under lOOOnm wavelength, and (f) showing the transient photocurrent under light illumination of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RIE etched Si using only SFe) at 0V bias.

[0049] Fig. 9

[0050] Fig. 9 is a scries of graphs showing the photocurrent density as a function of illuminated light power at (a) 365 nm and (b) 1000 nm of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RTE etched Si using SFe).

[0051] Fig. 10

[0052] Fig. 10 is a scries of graphs showing the (a) responsivity, (b) specific detectivity, (c) NPDR with a light intensity of 1.02 mA / cm2of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RIE etched Si using SFe) at -IV bias, (d) responsivity, (e) specific detectivity, and (f) NPDR with a light intensity of 1.02 mA / cm2of an embodiment of the present invention (RIE etched black Si using Ch and SFe) and comparative embodiments (planar Si, RIE etched Si using SFe) at -2V bias .

[0053] Fig. H

[0054] Fig. 11 is a series of images, with (a) showing the top -view optical image of a comparative embodiment (Gr / planar-Si device), (b) showing the top-view optical device of an embodiment of the present invention (Gr / black-Si device), (c) showing a schematic cross -section of the device structure of the present invention, and (d) showing the Raman spectrum of the transferred Gr monolayer onto the SiOj / Si substrate.

[0055] Fig. 12

[0056] Fig. 12 is a current voltage curve of an embodiment of the present invention (RIE etched black Si using GE and SFg) and comparative embodiments (planar Si, RTE etched Si using SFg) under one sun illumination.

[0057] Detailed Disclosure of Embodiments

[0058] Herein, the present invention provides an optoelectronic device as a solution for utilizing black silicon as a photodetector. The black silicon may be utilized together with graphene to form a Schottky junction. The silicon in the disclosed photodetector may be first pre-treated with CI2 to passivate its surface, before being etched with SF6, to form black silicon. The black silicon may then be brought into contact with a semiconductor such as graphene to form a Schottky junction.

[0059] The present invention provides a photodetector comprising black silicon, wherein the black silicon is silicon treated with a first etching gas comprising CI2, and a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCI3.

[0060] The inventors have surprisingly found that CI2 treatment may not affect the optical morphology and reflectance of the silicon surface. Advantageously, CI2 may passivate the silicon surface by terminating the dangling bonds present on the silicon surface, which may result in a reduction in the defect density of the silicon surface. This may lead to an advantageously longer carrier lifetime of the resulting passivated black silicon while preserving the morphology of the nanotextured surface.

[0061] Advantageously, black silicon treated with both CI2 and SFg may exhibit the highest lifetime as compared to black silicon that has been only treated with cither CI2 or SFe, as well as the lowest normalized defect density. The inventors have surprisingly found that the higher carrier lifetime may be achieved at low injection levels. Additionally, the disclosed black silicon may also advantageously achieve over-unity IQE through defect passivation, along with the photomultiplication effect associated with impact ionization by holes in black Si.

[0062] In some embodiments, the surface of the black silicon has a normalized defect density in a range of less than about 0.40, less than about 0.38, less than about 0.36, less than about 0.34, less than about 0.32, less than about 0.30, less than about 0.28, less than about 0.26, less than about 0.24, less than about 0.22, less than about 0.20, less than about 0.18, less than about 0.16, less than about 0.14, less than about 0.12, less than about 0.10, less than about 0.08, less than about 0.06, less than about 0.04, less than about 0.02, or 0, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0063] In some embodiments, the black silicon has one or more of the following X-ray photoelectron spectroscopy (XPS) peaks in a Cl 2p spectrum: 200 eV and 198.5 eV.

[0064] The black silicon may be utilized together with graphene or a metal oxide for use in a photodetector. In some embodiments, the photodetector further comprises graphene or metal oxide.

[0065] In some embodiments, the black silicon and graphene form a Schottky junction.

[0066] A photodetector comprising graphene and black silicon may advantageously exhibit superior optoelectronic properties such as responsivity, external quantum efficiency, internal quantum efficiency, short circuit current density (Jsc), and open-circuit voltage (Voc). The disclosed photodetector may also advantageously exhibit a synergistic effect arising from the combination of black Si nanotexturing, Gr / Si Schottky junction, and heterointerface passivation.

[0067] In some embodiments, the metal oxide is selected from the group consisting of indium tin oxide (ITO), and titanium oxide (TiO2).

[0068] In some embodiments, the second etching gas comprises SFe.

[0069] In some embodiments, the first and second etching gases are plasma.

[0070] In some embodiments, the photodetector is self-powered.

[0071] The disclosed photodetector may advantageously exhibit a high self-powered responsivity as compared to a photodetector without Ch treatment. The inventors have surprisingly found that without the Cl2 treatment, the built-in potential of the photodetector would not be sufficiently high for the photodetector to be self-powered. Advantageously, the transfer of Gr on a Cl-terminated surface may contribute to a higher built-in potential and improved self-powered performance, particularly if the Cl-terminated surface induces Gr doping.

[0072] The present invention also provides a method of preparing black silicon, comprising:

[0073] (i) pre-treating a silicon surface with a first etching gas comprising CI2; and

[0074] (ii) treating the pre -treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCI3 thereby forming black silicon.

[0075] In some embodiments, step (i) is performed at a pressure in a range of about 30 mTorr to about 70 mTorr, about 30 mTorr to about 65 mTorr, about 30 mTorr to about 60 mTorr, about 30 mTorr to about 55 mTorr, about 30 mTorr to about 50 mTorr, about 30 mTorr to about 45 mTorr, about 30 mTorr to about 40 mTorr, about 30 mTorr to about 35 mTorr, about 35 mTorr to about 70 mTorr, about 40 mTorr to about 70 mTorr, about 45 mTorr to about 70 mTorr, about 50 mTorr to about 70 mTorr, about 55 mTorr to about 70 mTorr, about 60 mTorr to about 70 mTorr, about 65 mTorr to about 70 mTorr, or about 30 mTorr, about 35 mTorr, about 40 mTorr, about 45 mTorr, about 50 mTorr, about 55 mTorr, about 60 mTorr, about 65 mTorr, about 70 mTorr, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that arc within the stated range(s).

[0076] In some embodiments, step (i) is performed at a temperature in a range of about 10 °C to about 30 °C, about 10 °C to about 25 °C, about 10 °C to about 20 °C, about 10 °C to about 15 °C, about 15 °C to about 30 °C, about 20 °C to about 30 °C, about 25 °C to about 30 °C, or about 10 °C, about 15 °C, about 20 °C, about 25 °C, about 30 °C, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). In some embodiments, step (i) is performed at a duration in a range of about 10 minutes to about 20 minutes, about 10 minutes to about 19 minutes, about 10 minutes to about 18 minutes, about 10 minutes to about 17 minutes, about 10 minutes to about 16 minutes, about 10 minutes to about 15 minutes, about 10 minutes to about 14 minutes, about 10 minutes to about 13 minutes, about 10 minutes to about 12 minutes, about 10 minutes to about 11 minutes, or about 10 minutes to about 20 minutes, about 11 minutes to about 20 minutes, about 12 minutes to about 20 minutes, about 13 minutes to about 20 minutes, about 14 minutes to about 20 minutes, about 15 minutes to about 20 minutes, about 16 minutes to about 20 minutes, about 17 minutes to about 20 minutes, about 18 minutes to about 20 minutes, about 19 minutes to about 20 minutes, or about 10 minutes, about 11 minutes, about 12 minutes, about 13 minutes, about 14 minutes, about 15 minutes, about 16 minutes, about 17 minutes, about 18 minutes, about 19 minutes, about 20 minutes or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0077] In some embodiments, step (i) comprises flowing the first etching gas at a flow rate in a range of about 20 seem to about 50 seem, about 20 seem to about 40 seem, about 20 seem to about 30 seem, about 30 seem to about 50 seem, about 40 seem to about 50 seem, or about 20 seem, about 30 seem, about 40 seem, about 50 seem, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that arc within the stated rangc(s) .

[0078] Tn some embodiments, step (ii) is performed at a pressure in a range of about 15 mTorr to about 55 mTorr, about 15 mTorr to about 50 mTorr, about 15 mTorr to about 45 mTorr, about 15 mTorr to about 40 mTorr, about 15 mTorr to about 35 mTorr, about 15 mTorr to about 30 mTorr, about 15 mTorr to about 25 mTorr, about 15 mTorr to about 20 mTorr, about 20 mTorr to about 55 mTorr, about 25 mTorr to about 55 mTorr, about 30 mTorr to about 55 mTorr, about 35 mTorr to about 55 mTorr, about 40 mTorr to about 55 mTorr, about 45 mTorr to about 55 mTorr, about 50 mTorr to about 55 mTorr, or about 15 mTorr, about 20 mTorr, about 25 mTorr, about 30 mTorr, about 35 mTorr, about 40 mTorr, about 45 mTorr, about 50 mTorr, about 55 mTorr, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0079] In some embodiments, step (ii) is performed at a temperature in a range of about 0 °C to about 20 °C, about 0 °C to about 15 °C, about 0 °C to about 10 °C, about 0 °C to about 5 °C, about 5 °C to about 20 °C, about 10 °C to about 20 °C, about 15 °C to about 20 °C, or about 0 °C, about 5 °C, about 10 °C, about 15 °C, about 20 °C, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s) .

[0080] In some embodiments, step (ii) is performed at a duration in a range of about 10 minutes to about 20 minutes, about 10 minutes to about 19 minutes, about 10 minutes to about 18 minutes, about 10 minutes to about 17 minutes, about 10 minutes to about 16 minutes, about 10 minutes to about 15 minutes, about 10 minutes to about 14 minutes, about 10 minutes to about 13 minutes, about 10 minutes to about 12 minutes, about 10 minutes to about 11 minutes, or about 10 minutes to about 20 minutes, about 11 minutes to about 20 minutes, about 12 minutes to about 20 minutes, about 13 minutes to about 20 minutes, about 14 minutes to about 20 minutes, about 15 minutes to about 20 minutes, about 16 minutes to about 20 minutes, about 17 minutes to about 20 minutes, about 18 minutes to about 20 minutes, about 19 minutes to about 20 minutes, or about 10 minutes, about 11 minutes, about 12 minutes, about 13 minutes, about 14 minutes, about 15 minutes, about 16 minutes, about 17 minutes, about 18 minutes, about 19 minutes, about 20 minutes or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated rangc(s).

[0081] Tn some embodiments, step (ii) comprises flowing the second etching gas at a flow rate in a range of about 20 seem to about 50 seem, about 20 seem to about 40 seem, about 20 seem to about 30 seem, about 30 seem to about 50 seem, about 40 seem to about 50 seem, or about 20 seem, about 30 seem, about 40 seem, about 50 seem, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub -ranges or discrete values (which may or may not be a whole number) that are within the stated range(s) .

[0082] The present invention further provides a method of preparing a photodetector, comprising:

[0083] (i) pre-treating a silicon surface with a first etching gas comprising Cl?;

[0084] (ii) treating the pre -treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, H2, O2, F2, or BCh to form black silicon;

[0085] (iii) applying graphene on the black silicon.

[0086] In some embodiments, the method further comprises:

[0087] (iv) applying a first metal electrode on a front surface of the black silicon, and a second metal electrode on a rear surface of the black silicon.

[0088] In some embodiments, the first and second metal electrodes comprise at least one metal selected from the group consisting of titanium (Ti), gold (Au), nickel (Ni), gallium (Ga), and indium(In).

[0089] Tn some embodiments, the method further comprises before step (iv): (iii-a) depositing SiOz on a front surface of the black silicon.

[0090] The present invention also provides black silicon produced by the method disclosed herein.

[0091] Exemplary, non-limiting embodiments of the disclosed catalysts, methods of producing them, and uses thereof will now be disclosed.

[0092] Examples

[0093] Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

[0094] Example 1: Fabrication of Graphene / black-Silicon Schottky junction device

[0095] N-type (100) CZ Si wafers with a resistivity of 1-10 IT cm. a thickness of 525 pm, and a single-side polished surface were used herein. The polished surfaces were first exposed to CI2 plasma as a pretreatment for surface passivation before texturing with SFe plasma. Both plasma treatments were performed using an inductively coupled plasma (TCP) RTE system (Oxford PlasmaProlOO). The detailed RIE conditions for Cb-plasma pretreatment were chamber pressure of 50 mTorr, process temperature of 20 °C, RF power of 200 W, TCP power of 0 W, He backing flow of 8sccm, CI2 gas flow of 35 seem, and plasma time of 15 min. For the SIT plasma RIE step, 35 mTorr chamber pressure, 5 °C process temperature, 50 W RF power, 1500 W ICP power, 1.5 A magnetic ring current, 10 seem He backing flow, 47 seem Oz flow rate, 36 seem SFg flow rate and 15 min process time were used.

[0096] After the RIE process, the samples were cleaned in acetone, isopropyl alcohol (IP A), and DI water with ultrasonication, followed by the deposition of a 300 nm SiOz layer on the nanotextured surface using PECVD (Cello Aegis-20). Photolithography and 5% HF solution were employed for patterning and etching the SiOz layer. The front surface was then deposited with Ti (5 nm) / Au (100 nm) using an e-beam evaporator. The rear-side metal electrode was formed by a Ga-In eutectic alloy (Gallium-lndium eutectic, Sigma-Aldrich).

[0097] A graphene (Gr) monolayer was grown on Cu foils using CVD (Graphene on Cu foils, 2D Semiconductors), then covered with PMMA (PMMA 495 A2, MicroChem) by spin coating at 3000 rpm for 30 seconds. PMMA / Gr / Cu was then dried in a fume hood at room temperature for one day. To etch the Cu foil, the samples were placed in a Cu etchant solution (Cu etchant, Sigma -Aldrich) for 1 hour. Subsequently, the PMMA / Gr was floated in ultrapure deionized water for one day to remove Cu residue. The cleaned PMMA / Gr was transferred onto the target substrate and dried for 10 minutes on a 70 °C hot plate to improve the adhesion between Si and Gr. After drying, the PMMA layer was removed by immersing the sample in hot Acetone for 30 minutes. Finally, for doping of the Gr monolayer, the sample was flipped and exposed to HNOs fumes (Nitric acid, Sigma- Aldrich) for 30 seconds. A schematic of the fabrication may be found in Figure 1.

[0098] Example 2: Characterization of black silicon layer

[0099] Example 2a: General characterization procedures

[0100] The surface morphology of the black Si substrates was observed with a field emission scanning electron microscope (FESEM, Thermo Fisher Scientific, Apero-S). X-ray photoelectron spectroscopy (XPS, Kratos, AXIS Supra) was employed to analyze the surface composition of Si after plasma treatment. The optical reflectance as a function of wavelength was measured by an ultraviolet - visible (UV-V1S) spectrophotometer (Shimadzu, UV-2450). The transferred Gr monolayer on a SiOz / Si substrate was analyzed by a Raman spectrometer (Horiba, LabRAM HR Raman Instrument). The effective carrier recombination lifetime was measured using a quasi -steady state photoconductance (QSSPC) measurement system (Sinton instrument, WCT-120). Dark and photocurrent- voltage curves were measured using a homemade setup which includes a semiconductor parameter analyzer (Kcithlcy, 2636B Sourccmctcr), microscope, and probe station. The photodetection properties in the UV to near-infrared (NIR) region were characterized using an Xe lamp (Horiba, EPS 100) equipped with a monochromator, covering a wavelength range of 300-950 nm. For the characterization of photovoltaic properties, a solar simulator (San-EI Electric, XEC-301S) with an Xe lamp and AM 1.5G spectrum was utilized, providing an irradiance of 100 mW / cm2. The light intensity was calibrated separately for both measurements using a power meter (Thorlabs, PM100A) and a standard silicon photovoltaic cell.

[0101] Example 2b: Characterization of black silicon layer

[0102] The optical properties of black Si with and without pretreatment were evaluated by cross- sectional scanning electron microscope (SEM) images and reflectance measurements, as shown in Figure 2. Black Si with Ch-plasma pretreatment exhibited a morphology similar to that of black Si without pretreatment (Figs. 3a-3c).

[0103] The aspect ratio of black Si without pretreatment was determined to be 0.94 with an average height of 164 nm and width of 174 nm, while its counterpart showed an aspect ratio of 0.98 with an average height of 221 nm and width of 218 nm. These results suggest that the pretreatment had little effect on the nanotextured morphology, as the aspect ratios and dimensions of the structures remained relatively similar between the two samples. Moreover, this implies that the reflectance of the two samples is comparable since the reflectance of the nanotextured surface is mainly influenced by the aspect ratio. Reflectance measurements conducted within the wavelength of 250 to 800 nm (Fig . 2e) demonstrate no significant difference between black Si with and without pretreatment. Fig. 2a-2d show that the optical morphology of the Si surface before and after treatment remain relatively similar. Therefore, the CF plasma pretreatment does not affect the optical morphology and reflectance of black Si.

[0104] The passivation effect of Cl2 plasma pretreatment was evaluated by measuring the effective carrier recombination lifetime. The effective carrier lifetime is determined by three recombination mechanisms: radiative, Shockley-Read-Hall (SRH), and Auger recombination. The carrier lifetime is expressed by the equation: where r is the effective carrier recombination lifetime, rlad is the radiative recombination lifetime, TSRH is the SRH recombination lifetime, an is the Auger recombination lifetime. At low injection levels, SRH recombination dominates and determines the effective carrier lifetime, while at high injection levels (> 1016cm '), Auger recombination becomes dominant. As the radiative recombination lifetime is higher than the other two lifetime values, the radiative recombination lifetime docs not significantly affect the effective carrier lifetime. SRH recombination occurs through deep-level states created by various defects, including vacancies and impurities. These defects are categorized by location, either at the bulk or surface. Consequently, tire SRH recombination lifetime is determined by bulk (rb) and surface recombination (rs) lifetime.

[0105] Given the high bulk lifetime of CZ c-Si wafers, surface recombination primarily determines the SRH recombination lifetime. The surface recombination (r,) is expressed as a function of surface recombination velocity: where, w is the wafer thickness, and S is the surface recombination velocity. The factor of 2 accounts for the two surfaces (front and rear). The equation for the surface recombination velocity is: where o is the capture cross-section, n, is the density of deep-level surface states, and v,h is the thermal velocity of carriers. Substituting equations (4) into (3), ns is given by:

[0106] From this equation, the density of surface defect states is inversely proportional to the carrier lifetime, which is shown in Figure 4c.

[0107] Figure 4a shows the lifetime curves at various injection levels, indicating an overall increase in lifetime by CI2 plasma pretreatment. Figure 4b demonstrates the lifetime at one sun intensity, corresponding to an injection level of 5xl013cm3. This specific injection level was selected, considering that one sun illumination intensity (100 mW / ni2) is the standard measurement condition for evaluating solar cell performance. In Figure 4b, the pretreatment resulted in an enhancement in carrier lifetime, with an increase from 6.50 to 10.19 ps in planar Si and from 14.70 to 16.65 ps in black Si, suggesting a decrease in defect density. The vertical and horizontal shift in lifetime indicates changes in defect density and field effect, respectively. Comparing the lifetime curves of planar Si and black Si treated with CI2 and SFe, the lifetime shifted both vertically and horizontally, indicating that the carrier lifetime is affected by both a change in defect density and the field effect. It is known that nanotexturing a c-Si wafer with 18 ps results in a low lifetime of 0.8 ps due to the metal particles used for the nanotexturing process, highlighting the efficacy of the plasma treatment in enhancing carrier lifetime.

[0108] Furthermore, un-passivated planar Si typically exhibits a poor lifetime of less than 10 ps, primarily due to the high surface recombination rate. Therefore, the observed increase in lifetime in plasma-treated samples can be attributed to improved surface passivation. This finding aligns with known results, where surface treatment on a silicon wafer without a passivation layer results an increase in lifetime.

[0109] Figure 4c presents the normalized defect density, evaluated by the inverse of the lifetime obtained from the QSSPC. It was observed that fluorine (F) plasma reduces the normalized defect density to 0.44, while Cl decreases it to 0.64, indicating that F has a higher passivation effect compared to Cl. The sample treated with both CI2 and SFe exhibits the highest lifetime of 16.7 ps and the lowest normalized defect density of 0.39, attributed to the combined passivation effect of Cl and F. Although the higher lifetime observed in Si treated with SF& plasma, as shown in Figure 4b, suggests that F has the predominant passivation effect, it is important to note that the higher lifetime was achieved in Ch-treated black Si at low injection level.

[0110] Furthermore, black Si treated with both Ch and SF« exhibits an even higher lifetime compared to Ch-trcatcd and SFe-trcatcd samples under low injection conditions (Figure 4a). Considering that photodetectors operate under low-intensity light conditions, these result emphasize the importance of CI2 treatment in enhancing self-powered photoresponse characteristics under low-injection light conditions. As a result, the comparison of the optical and electrical properties of black Si confirms the passivation effect of CI2 plasma treatment on the nanotextured surface which leads to an increase in carrier lifetime while preserving the morphology of the nanotextured surface.

[0111] Figure 5 shows the XPS spectra which compares the elemental composition and oxidation states of Si wafers treated with different plasma conditions. Regardless of die plasma treatment, Figures 5a and 5b demonstrate the presence of elemental Si and S1O2 in all samples. In Figure 5c, the appearance of the F Is peak was exclusively observed in the samples treated with ShT plasma, which is consistent with previously reported results. This observation suggests that the SIT plasma not only caused structural modification but also resulted in the formation of a fluorine-terminated Si surface. In Figure 5d, a strong Si 2s plasmon line (201.5 eV) was detected. Notably, the Cl 2p typically appears as a doublet, with the main peak intensity being twice that of the minor peak (in a 2:1 ratio) due to the p orbital. Therefore, the detected XPS peak of bare Si in Cl 2p is attributed to the Si 2s plasmon, indicating the absence of Cl. Only the sample treated with Clz plasma showed a weak peak intensity close to the Cl binding energy (200 eV and 198.5 eV), suggesting the presence of a low concentration of Cl on the surface.

[0112] It is noteworthy that both F and Cl can passivate the Si surface by terminating the dangling bonds present on the silicon surface, as they require only one additional electron to complete their valence shell, similar to hydrogen. Wet chemical functionalization using HF, HC1, or Dimethylaluminum chloride has been the conventional approach for passivating the Si surface with F and Cl. The detection of F and Cl in the samples exposed to SF& and CI2 plasma provides compelling evidence of improved surface passivation quality, in addition to the observed increase in effective lifetime as shown in Figure 4. The mechanism underlying the passivation and nanotexturing of black Si is described in Figure 6.

[0113] Example 3: Characterization of Gr / Si Schottky junction device

[0114] Figure 7 presents the photoresponse characteristics of the fabricated Gr / Si photodetectors operating in self-powered mode. Notably, the remarkable self-driven performance was exclusively observed in the CI2 pl as ma- treated device, indicating the attainment of a strong built-in potential solely in the device. This is further corroborated by the lifetime results, where a substantially higher lifetime was achieved in black Si treated with both Ch and SFs at low injection levels, compared to Si treated with CI2 or Sly, alone. As shown in Figure 7a, the responsivity of black Si photodetectors with CI2 treatment exceeded that of both untreated black and planar Si devices, closely approaching the values of ideal photodiodes. The peak responsivity was observed at 800 nm, where CD plasma- treated black Si demonstrated a 580 mA / W responsivity, while black Si without CD treatment and planar Si showed 4.25 and 0.943 mA / W, respectively.

[0115] Figure 7b shows the EQE and internal quantum efficiency (IQE) of the fabricated devices. Interestingly, Gr / black-Si with CI2 treatment exhibited remarkably high IQE values, surpassing even the theoretical maximum of 100% at 300 nm. The phenomenon of over-unity IQE in Si photodiodes can be explained by impact ionization and carrier multiplication.

[0116] Additionally, nanotextured black Si with a passivated surface has shown that it can achieve over-unity IQE through the effective utilization of multiple carrier generations by impact ionization, facilitated by low bandgap, minimized recombination, and the strong electric field of black Si. However, achieving over-unity IQE in Gr / Si photodiodes has been challenging, possibly due to reduced earner absorption in Si and defects induced at the Gr-Si interface. Therefore, the observed over-unity IQE value in Gr / black-Si can be mainly attributed to the defect passivation, along with the photomultiplication effect associated with impact ionization by holes in black Si. The achieved extremely low reflectance (~1%) in black Si further contributes to the over-unity EQE. Considering the critical influence of passivation quality on the photomultiplication effect, it can be deduced that a combination of two different passivation elements (Cl, F) is required to enhance passivation quality and low-injection lifetime, contributing to the improvement of both self-powered photoresponse and EQE. It is worth noting that this represents the first demonstration of Gr / Si photodetectors achieving an over-unity IQE value. This further proves the synergistic effect arising from the combination of black Si nano texturing, Gr / Si Schottky junction, and heterointerface passivation, successfully yielding high performance that exceeds the IQE of ideal photodiodes. In Figure 8a, the dark and photocurrent-voltage curves of the photodetector are shown, measured under 532 nm light illumination with an intensity of 12.6 mW / cm2at room temperature. The dark current densities of the devices at 0 V were determined as 5.96 pA / cm2for Gr / planar-Si, 4.14 uA / cm2for Gr / black-Si without pretreatment, and 1.00 pA / cm2for Gr / black-Si with pretreatment. The higher dark current values observed in planar Si and black Si without pretreatment compared to black Si with pretreatment can be attributed to multiple factors, including the presence of crumpled Gr, an un-passivated surface, and the formation of interfacial defects, such as Cu residues. Moreover, the lower dark current observed in the Ch-treated black-Si photodetector, compared to the non-treated black Si device, confirms the effectiveness of Clz plasma passivation on the nanotextured surface, leading to a reduced dark current.

[0117] The Schottky barrier height (SBH) of the Gr / Si junctions was calculated using a modified approach, which accounts for the unique material properties of graphene (Gr) when forming a junction with silicon (Si). where Jois reverse saturation current, 2.JJ is nonconserving k scattering strength =1.11x10

[0118] 12, Vj_ is out of plane velocity = 3.7 x 10scm / s, q is the elementary charge is spin-valley degeneracy = 4 hottky barrier height measured from zero energy = 0.5 e is Boltzmann constant, T is temperature, Z±is thickness of graphene layer = 0.345 nm (monolayer), h is reduced Planck constant, vFis Fermi velocity = 10scm / s, is Schottky barrier height, and scFis characteristic kinetic energy of charge carriers = 50 meV.

[0119] Using this equation, the SBH values were calculated for different configurations of the Gr / Si junctions as follows:

[0120] These SBH values indicate a significant increase compared to those determined using the classical thermionic emission theory. This increase can be attributed to the more accurate representation of charge carrier transport at the 2D / 3D Gr / Si interface, as captured by the modified theory.

[0121] Photodetector performance was quantitatively evaluated by calculating the following crucial figure-of merits: responsivity I, on-off ratio (Iphoto / Idark), EQE, IQE, detectivity (P*), and normalized photo-to-dark current ratio (NPDR) according to the following equations. where IPhOio, PM, PA, h, c, e, Abs, and A are photocurrent, dark current, incident light intensity, Planck’s constant, the speed of light, the elementary charge, absorption rate, and the area of the photodetector, respectively.

[0122] The Ch plasma-treated Gr / black-Si photodetector exhibits excellent self-powered responsivity of 408.5 mA / W, with a highest on-off ratio of 3788 under 532 nm laser illumination at zero voltage. Tn comparison, devices without pretreatment showed low on-off ratios, with the planar and black Si photodetectors without pretreatment exhibiting on-off ratios of 1.10 and 1.68, respectively (Table 1). Figures 8b and 8c show detectivity and NPDR of the fabricated Gr / Si photodetectors as a function of wavelength, which are calculated using Equations (10) and (11). As a result, Gr / black-Si photodetectors with pretreatment showed much higher NPDR values compared to Gr / planar-Si and Gr / black-Si without pretreatment, due to its lower dark current and higher responsivity. Moreover, black Si with pretreatment exhibited higher self-powered photodetection performance, with a detectivity of 1.02xl012cm-Hz1 / 2 / W and NPDR of 1.82xl07W1, compared to Gr / planar-Si and Gr / black-Si without pretreatment. The detectivity and NPDR for Gr / planar-Si were 5.16x108 cm-Hz1 / 2 / W and 4.29xl0 W- 1while for Gr / black-Si without pre treatment, the values were 2.02x109 cm-Hz1 / 2 / W and 2.29x 104W- 1, respectively.

[0123] This finding further suggests that the built-in potential of the Gr / planar-Si and Gr / black-Si devices without the pretreatment is not sufficiently high, resulting in poor self-powered characteristics. The reduced built-in potential of these devices can be attributed to the presence of high interface defects between Gr and Si, which consequently leads to carrier recombination loss. Moreover, it is plausible that the transfer of Gr onto Cl-terminated Si leads to partially and weakly chlorinated Gr, considering the substantial performance improvement observed in Cl 2- treated Gr / black-Si, which cannot be solely explained by enhanced lifetime. The transfer of Gr on a Cl- terminated surface may contribute to a higher built-in potential and improved self-powered performance, particularly if the Cl-terminated surface induces Gr doping. It is known that chlorination of Gr results in p-type doping and increased bandgap energy. Unlike conventional methods for Gr doping such as HNO3 fume exposure or plasma treatment on Gr layers, there is a lack of studies demonstrating Gr doping achieved by plasma-treated surfaces.

[0124] The photocurrents were measured under different incident light powers to evaluate the photocurrent gain mechanism in the fabricated photodetectors. Figure 8d shows the photocurrent density as a function of illuminated light power at 532 nm wavelength. The result showed that Gr / black-Si photodetectors without pretreatment exhibit much lower photocurrent under zero bias compared to that of Gr / black-Si photodetectors with the pretreatment. The power intensity -dependent photocurrent was fitted to extract the empirical coefficient. The power law to fit the intensity - photocunent curve follows: where C and 0 are a constant and the empirical coefficient, respectively.

[0125] The extracted values of 0 were 0.01 , 0.03, and 0.84 under 532 nm laser illumination for Gr / planar-Si, Gr / black-Si without pretreatment, and Gr / black-Si with pretreatment, respectively. These values indicate that photogenerated carriers are trapped at the metal-semiconductor interface for the devices without pretreatment. In an ideal trap-free photodetector, the 0 value is equal to 1. The 0 value close to 1 for Gr / black-Si photodetectors with pretreatment suggests that trap / defect effects are trivial. Meanwhile, a low 0 value was observed in Gr / planar-Si and Gr / black-Si photodetectors without pretreatment, with a 0 value close to 0. This indicates the presence of complex electron-hole generation, and the transport of the photogenerated carriers is impeded by trap-assisted recombination and defect-related processes in these devices. Figure 9 depicts the photocurrents under UV (365 nm) and NIR (1000 nm) light illumination at different power densities at zero bias.

[0126] At shorter wavelengths (532 nm (Figure 8) and 365 nm (Figure 9a)), the higher 0 values observed for the Gr / black Si (Cb+SFe) suggest effective passivation of surface states, reducing trap- assisted recombination and leading to photocurrent scaling close to the ideal value of 1. This indicates that the treatment significantly improves the surface quality and reduces defect-related recombination at the metal -semiconductor interface.

[0127] In contrast, at 1000 nm (Figure 9b), the light penetrates deeper into the Si, where bulk recombination mechanisms become more prominent. The higher power -law exponents observed in the untreated samples at this wavelength may be due to the greater influence of bulk carrier generation and recombination, which are less affected by surface treatments. The Ch treatment, while beneficial for surface passivation, may not substantially impact bulk recombination dynamics, resulting in a lower 0 value at 1000 nm for the treated sample. This wavelength-dependent behavior underscores the complex interplay between surface and bulk effects in determining the photocurrent response in these devices.

[0128] Additionally, Table 1 summarizes the self-powered photodetection performance of the fabricated devices. The results consistently demonstrate enhanced self-powered performance for Cfl- treated Gr / black-Si photodetectors. The higher SBH and lower surface defects resulting from Cl 2 plasma treatment facilitate better control of carrier transport, leading to improved self -biased responsivity. It is also confirmed that Gr / black-Si photodetectors with pretreatment exhibited excellent responsivity under the applied bias (Figure lOa-lOf), reaching 1.3 and 0.94 A / W at -2 and - 1 V.

[0129] Table 1. Performance summary of fabricated Gr / Si Schottky junction photodetectors under UV (365 nm), VIS (532 nm), and NIR (1000 nm) laser illumination at 0 V bias

[0130] Dark

[0131] , W,,ave ,lengthr[ 1 current Responsivityct, Detectivity NPDR s nm] d ,ensi .t.yr[mA * / W] ~ On-off ratior[cm- „Hz1 / 2 / W] [ / W]

[0132] Tn addition, the time-dependent photoresponse was evaluated under 1000 nm wavelength light illumination at an intensity of 3.32 mW / cm2without applied bias (Figure 8e). Gr / planar-Si exhibited limited on-off photoresponse, influenced by its poor lifetime, as observed in Figure 4b. In contrast, Gr / black-Si devices demonstrated outstanding on-off photorcsponsc, with on-off ratios of l.OlxlO3and 4.63 for Ch-treated and untreated Gr / black-Si, respectively. The rise and decay times for Ch- treated Gr / black-Si were measured at 22.80 and 20.98 ms, while Gr / black-Si without pretreatment exhibited 13.50 and 5.11 ms, respectively. (Here, the rise and decay time denotes the time for the photocurrent to rise from 10% to 90% and fall from 90% to 10% during on and off illumination cycles.) The observed trade-off between responsivity and response time is attributed to carrier lifetime, as increased carrier lifetime results in higher responsivity and longer response times. Figure 5f illustrates the changes in on-off ratios under different wavelength light illuminations for Ch-trcatcd Gr / black-Si, revealing on-off ratios of 1014, 731.1, and 442.4, and rise / decay times of 22.80 / 20.98, 18.92 / 24.62, and 17.10 / 17.10 ms under 1000, 900, and 532 nm wavelength illuminations, respectively (Figure 8f). The higher on-off ratio at longer wavelengths correlates with the higher responsivity observed in Figure 7a.

[0133] The results demonstrate significant enhancements in the self-powered performance of Ch- treated Gr / black-Si photodetectors compared to non -treated Gr / black-Si devices across the UV-VIS- NTR range. The Gr / black-Si photodetector with Cl2 pretreatment exhibited a considerably higher responsivity of 409 mA / W, which is 178 times greater than that of the untreated Gr / black-Si photodetector (2.3 mA / W) at a wavelength of 532 nm. This improvement indicates that the Ch-treated photodetector achieved a sufficiently high built-in potential necessary for self-powered characteristics. These findings also underscore the critical impact of surface passivation on the device performance of black Si photodetectors.

[0134] Additionally, the optical microscopy images of the fabricated devices and the Raman spectrum are depicted in Figure 11. The results demonstrate that the obtained Raman spectrum provides clear evidence of the Gr monolayer as well as its high quality, as indicated by the low intensity of the D peak (~1350 cm i.

[0135] The photovoltaic performance of the Gr / black-Si solar cells was evaluated, as depicted in Figure 12. The Ch plasma-treated Gr / black-Si cell exhibited improved photovoltaic performance, including higher efficiency, short-circuit current (Jsc), open-circuit voltage (Voc), and fill factor, attributed to the enhanced surface passivation achieved through Cl 2 treatment. The efficiency of the Ch plasma-treated cell reached 2.33%, representing a notable improvement compared to the 0.31% efficiency observed in Gr / black-Si solar cells without pretreatment (Table 2). The low efficiency observed in Gr / planar-Si cell can be attributed to various factors, such as poor wafer quality, the absence of anti-reflection layer, and insufficient Gr doping. Commercially available Si wafers, specifically Cz-grown c-Si wafers with low lifetime, were employed. Regarding the Gr / black-Si solar cell without pretreatment, the low efficiency can be attributed to poor wafer quality and the enlarged surface area resulting from nanotexturing. The Jsc of the Ch plasma-treated Gr / black-Si solar cell reached an impressive value of 25.9 mA / cm2(Table 2). This achievement highlights the significant enhancement in photovoltaic performance facilitated by the Cl? pretreatment. Improved surface passivation and excellent light absorption properties obtained from the CI2 pretreatment are key factors contributing to the high Jsc-

[0136] . In brief, Gr / black-Si with pretreatment exhibited a notably higher efficiency of 2.33 %, surpassing that of Gr / black-Si without pretreatment and Gr / planar-Si, which achieved efficiencies of 0.31% and 0.05%, respectively. Furthermore, the average values in Table 2 further demonstrate the reproducibility of the fabricated devices discussed herein.

[0137] Tabic 2. Performance comparison of solar cells based on Gr / nanostructurcd Si

[0138] Comparative Examples

[0139] Comparative Example 1:

[0140] A comparison of photodetector properties relating to the performance of known Gr / nanostructured-Si photodetectors is shown in Table 3. It can he seen that the Gr / black-Si device presented herein demonstrates an excellent responsivity among reported Gr / black-Si photodetectors. The outstanding self-powered performance highlights the critical impact of surface passivation and Gr functionalization on enhancing device performance, facilitated by Ch plasma treatment. Furthermore, the method employed for black-Si texturing and passivation used herein is more beneficial and easier to integrate, considering MACE requires metal deposition and subsequent wet etching processes. In contrast, a one-step black-Si texturing process with ICP-RIE was utilized, seamlessly integrating surface passivation using the same equipment.

[0141] Table 3. Performance comparison of photodetectors based on Gr / n anostructured Si

[0142] Industrial Applicability

[0143] The present invention relates to optoelectronic devices. The devices of the present invention may be useful as solar cells, photodetectors, and batteries. Thus, this invention is capable of industrial applicability.

[0144] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

CLAIMS1. A photodetector comprising black silicon, wherein the black silicon is silicon treated with a first etching gas comprising Cl2, and a second etching gas comprising at least one of SF(1, CF4, CHF3. NF4, HBr, H2, O2, F2, or BC13.

2. The photodetector of claim 1 , wherein the surface of the black silicon has a normalized defect density of less than 0.4.

3. The photodetector of claim 1 or 2, wherein the black silicon has one or more of the following X- ray photoelectron spectroscopy (XPS) peaks in a Cl 2p spectrum: 200 eV and 198.5 eV.

4. The photodetector of any one of claims 1 to 3, further comprising graphene or metal oxide.

5. The photodetector of claim 4, wherein the black silicon and graphene form a Schottky junction.

6. The photodetector of claim 4, wherein the metal oxide is selected from the group consisting of indium tin oxide (ITO), and titanium oxide (TiO2).

7. The photodetector of any one of claims 1 to 6, wherein the second etching gas comprises SF().

8. The photodetector of any one of claims 1 to 7, wherein the first and second etching gases are plasma.

9. The photodetector of any one of claims 1 to 8, wherein the photodetector is self-powered.

10. A method of preparing black silicon, comprising:(i) pre-treating a silicon surface with a first etching gas comprising Cb; and(ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3, NF4, HBr, Hz, O2, F2, or BCb thereby forming black silicon.

11. The method of claim 10, wherein step (i) is performed at a pressure of about 30 mTorr to about 70 mTorr, a temperature of about 10 °C to about 30 °C, and a duration of about 10 to about 20 minutes.

12. The method of claim 10 or 11, wherein step (i) comprises flowing the first etching gas at a flow rate of about 20 to about 50 seem.

13. The method of any one of claims 10 to 12, wherein step (ii) is performed at a pressure of about 15 to about 55 mTorr, a temperature of about 0 °C to about 20 °C, and duration of about 10 to about 20 minutes.

14. The method of any one of claims 10 to 13, wherein step (ii) comprises flowing the second etching gas at a flow rate of about 20 to about 50 seem.

15. The method of any one of claims 10 to 14, wherein the second etching gas comprises SFe.

16. The method of any one of claims 10 to 15, wherein the first and second etching gases are plasma.

17. A method of preparing a photodetector, comprising:(i) pre-treating a silicon surface with a first etching gas comprising Cl2;(ii) treating the pre-treated silicon surface with a second etching gas comprising at least one of SFe, CF4, CHF3. NF4, HBr, H2, O2, F2, or BCb to form black silicon;(iii) applying graphene on the black silicon.

18. The method of claim 17, further comprising:(iv) applying a first metal electrode on a front surface of the black silicon, and a second metal electrode on a rear surface of the black silicon.

19. The method of claim 18, wherein the first and second metal electrodes comprise at least one metal selected from the group consisting of Ti, Au, Ni, Ga, and In.

20. The method of any one of claims 17 to 19, further comprising before step (iv):(iii-a) depositing SiO on a front surface of the black silicon.

21. Black silicon produced by the method of any one of claims 10 to 16.

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