On-chip micro spectrometer and spectral imager based on photoelectric cascade diode epitaxial structure

Abstract

The invention provides an on-chip integrated micro spectrometer based on a cascade diode epitaxial structure and a spectral imager. The on-chip integrated micro spectrometer comprises a substrate, a photoelectric cascade diode epitaxial structure located on the substrate and an electrode, the photoelectric cascade diode epitaxial structure comprises at least two vertically cascaded photodiodes, and each photodiode, as a light detector, can generate spectral response for spectrums in different spectral ranges. The spectral response curve of each photodiode is adjustable along with the change of incident light spectral information and / or external bias voltage, and high-precision spectral measurement, analysis and spectral imaging are realized.

Description

Technical Field

[0001] The present disclosure relates to the fields of optoelectronics and semiconductor technologies, and in particular, to an on-chip micro spectrometer and a spectral imager based on an optoelectronic cascade diode epitaxial structure. Background Art

[0002] Optical spectrometers are widely used in many fields such as material characterization, medical diagnosis, food science, and biosensing. Traditional bench-top spectrometers achieve high resolution in a wide spectral range by using dispersive elements, long optical paths, and complex mechanical systems. However, the traditional spectrometer design and device architecture result in an overly large instrument volume, a complex system, and high costs, which limit their integration in portable and wearable platforms. To meet the demand for compact, low-cost spectrometers and hyperspectral imaging systems, researchers have been working on miniaturizing spectrometers in recent years.

[0003] Current miniaturization methods are mainly divided into two categories. The first category follows the principle of traditional spectrometers and uses technologies such as dispersive optical devices, narrowband filter arrays, and Fourier transform spectroscopy to replace the dispersive element (spectroscopic grating) in traditional spectrometers, thereby classifying the light source to be measured into monochromatic light and finally guiding it to a photodetector for spectral resolution. Although this method significantly reduces the volume of the entire device compared to traditional bench-top spectrometers, limited by the optical path requirements, it is still difficult to reduce the device size to the sub-millimeter level, making it impossible to realize future portable and palm spectrometers, chips, and portable spectral imagers.

[0004] The second category of methods uses computational spectroscopy techniques and combines a broadband photodetector with tunable spectral response capabilities and superior algorithms to reconstruct spectral signals and spectral images. The current technical routes mainly include: preparing nanowires with compositional gradients, structural color silicon nanowire arrays, filter-encoded photodetector arrays, detector arrays with metasurfaces as filters, achieving spectral control based on the band alignment of two-dimensional materials, using black phosphorus transistors to modulate the bandgap using the Stark effect, and using a thin film structure with a gradually changing composition to realize a broadband photodetector with different spectral responses, and using the different potential barriers of organic materials and contact metals. However, the existing technical solutions are highly sensitive to material growth conditions, layer thickness, interface contact, and environmental factors, resulting in challenges for large-scale applications. Another problem is that due to the properties of the existing materials themselves and the limitations of current material growth and synthesis levels, the existing technical solutions have only realized spectrometers and spectral imagers in the visible and infrared bands and do not have the application ability and potential in the short-wavelength ultraviolet and deep ultraviolet bands. Summary of the Invention

[0005] In view of this, in order to solve at least one of the above-mentioned technical problems, the present disclosure provides an on-chip integrated micro spectrometer and a spectral imager based on a photoelectric cascade diode epitaxial structure.

[0006] In order to achieve the above object, the technical solution of the present disclosure is as follows:

[0007] An embodiment of the present disclosure provides an on-chip integrated micro spectrometer based on a cascade diode epitaxial structure, including a substrate, a photoelectric cascade diode epitaxial structure located on the substrate, and an electrode; wherein, the photoelectric cascade diode epitaxial structure includes at least two vertically cascaded photodiodes, and each photodiode can generate spectral responses for spectra in different spectral ranges as a photodetector, so that the spectral response curve of each photodiode can be adjusted with the change of incident light spectral information and / or external bias voltage, realizing high-precision spectral measurement, analysis and spectral imaging.

[0008] According to an embodiment of the present disclosure, the photoelectric cascade diode epitaxial structure at least includes a first photodiode and a second photodiode stacked in sequence from the substrate; the first photodiode generates a spectral response for the spectrum in the first spectral range as the first photodetector, and the response wavelength of the first spectral range is λ1, 10 nm ≤ λ1 ≤ 10000 nm, that is, the first response spectral range is within 10 nm to 10 μm; the second spectral range of the second photodiode as the second photodetector is different from the first spectral range.

[0009] According to an embodiment of the present disclosure, the photoelectric cascade diode epitaxial structure at least includes, from bottom to top: a first N-type semiconductor material layer (3), a first undoped semiconductor material layer (4), a P-type semiconductor material layer (5), a second undoped semiconductor material layer (6), and a second N-type semiconductor material layer (7); the first N-type semiconductor material layer (3), the first undoped semiconductor material layer (4), and the P-type semiconductor material layer (5) constitute the first photodiode; the P-type semiconductor material layer (5), the second undoped semiconductor material layer (6), and the second N-type semiconductor material layer (7) constitute the second photodiode.

[0010] According to an embodiment of the present disclosure, the material components of the first undoped semiconductor material layer (4) and the second undoped semiconductor material layer (6) are different, so that the coverage ranges of the spectral responses of the first photodiode and the second photodiode are different; the spectral response range of the on-chip integrated micro spectrometer covers the spectral range from 10 nm to 10000 nm and within this range.

[0011] According to an embodiment of the present disclosure, the on-chip integrated micro-spectrometer further includes a functional layer located on top of the optoelectronic cascade diode or at the bottom of the substrate, which can further integrate functions capable of regulating the optical information of the incident light. The optical information includes wavelength, optical power, light polarization, and optical phase.

[0012] According to an embodiment of the present disclosure, the cross-sectional area of the optoelectronic cascade diode device in the horizontal direction is 1 nm 2 -1000 mm 2 , and the cross-sectional shape includes: circular, rectangular, regular polygon or irregular shape; the optoelectronic cascade diode structure can be a thin film structure, a nanowire structure, a nanorod structure and other irregular structures.

[0013] According to an embodiment of the present disclosure, the implementation methods of the optoelectronic cascade diode epitaxial structure include: realized by epitaxial growth of materials, realized by physical transfer, realized by mechanical exfoliation, and realized by van der Waals contact based on low-dimensional materials.

[0014] According to an embodiment of the present disclosure, the preparation materials of the substrate are selected from semiconductors including sapphire, silicon, germanium, silicon carbide, gallium oxide, boron nitride, diamond, aluminum nitride, gallium nitride, gallium arsenide, indium phosphide, or quartz glass or materials that are transparent to light in the wavelength range from deep ultraviolet light to infrared light. The preparation materials of the electrodes are selected from Ti, Al, Ni, Au, Cr, Pt or their combinations.

[0015] According to an embodiment of the present disclosure, the preparation materials of each layer in the optoelectronic cascade diode epitaxial structure are selected from binary, ternary or quaternary metal nitrides of Ga, Al, In, or binary, ternary or quaternary metal phosphides of Ga, Al, In, or binary, ternary or quaternary metal arsenides of Ga, Al, In, or binary, ternary or quaternary metal antimonides of Ga, Al, In; each layer of materials in the optoelectronic cascade diode epitaxial structure is selected from materials with fixed components, or materials with gradually changing components, or materials with stepped changes or non-linear increase and decrease changes corresponding to the same family of materials as described above; the thickness of each layer in the optoelectronic cascade diode epitaxial structure ranges from 0.1 nm to 5 μm.

[0016] Another embodiment of the present disclosure further provides a spectral imager based on the on-chip integrated micro-spectrometer array described in any one of the above. The control method of the micro-spectrometer array is that each micro-spectrometer unit is individually controlled by an external circuit, or multiple micro-spectrometer units are controlled in parallel, in series, or in a combination of series and parallel to achieve high-precision spectral detection, spectral analysis, and spectral imaging of wide-spectrum incident light. Description of the Drawings

[0017] Through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, the above and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0018] Figure 1 It is a schematic structural diagram of an on-chip integrated micro-spectrometer based on a photoelectric cascade diode epitaxial structure according to an embodiment of the present disclosure.

[0019] Figure 2 It is a schematic diagram of a micro-spectrometer containing two groups of photoelectric cascade diode epitaxial structures according to an embodiment of the present disclosure.

[0020] Figure 3 It is a schematic diagram of the performance test results of the micro-spectrometer according to an embodiment of the present disclosure.

[0021] Figure 4 It is a schematic diagram that the miniaturized spectrometer according to an embodiment of the present disclosure can detect and analyze the spectrum within the range of 10 nm - 10000 nm by optimizing and selecting materials with different components.

[0022] Figure 5 It is a schematic structural diagram of an on-chip micro-spectrometer integrated with a functional layer having spectral information regulation ability according to an embodiment of the present disclosure.

[0023] Figure 6 It is a schematic diagram of a spectral imager based on an on-chip integrated micro-spectrometer array according to an embodiment of the present disclosure. Detailed implementation manners

[0024] The present disclosure provides a miniature spectrometer and a spectral imager based on a photoelectric cascade diode epitaxial structure. First, the photoelectric cascade diode epitaxial structure is a special diode structure formed by two PN-junction diodes back-to-back in a cascaded manner, namely, an N-P-N structure. The NP-junction photodiode located at the bottom of the photoelectric cascade diode has a wide spectral response (including the spectrum within a certain wavelength range, from short wavelength to long wavelength), and can generate a varying photocurrent response to incident light of different wavelengths. Second, the PN-junction photodiode located at the top has a narrow spectral response to long-wavelength light, so that under the irradiation of long-wavelength light, a photocurrent response in the opposite direction to that of the bottom diode is generated. Since these two diodes located at the bottom and the top respectively form a new type of photodiode through a cascaded manner, and the two diodes respectively generate their own light responses to light of different wavelengths, and the directions of photocurrent flow are opposite. Therefore, a special phenomenon of photocurrent cancellation occurs inside this new type of cascaded photodiode, that is, the photo-generated carriers generated in the two PN-junctions will cancel each other out due to the opposite flow directions in the device, that is, an internal competition mechanism of photocurrent will be generated. Moreover, under different bias voltage conditions, the band offset trend of the two internally cascaded diodes in the new type of cascaded photodiode will change, thereby changing the direction and magnitude of the photocurrent flow, resulting in the final output spectral response curve being adjustable with the change of the bias voltage, and under the irradiation of light of different wavelengths, the spectral response curve (photocurrent vs. wavelength curve) also changes accordingly. Therefore, through a deep neural network calculation and reconstruction algorithm, the spectral response curves obtained based on different bias voltages are trained. Based on this, when an unknown light is incident, the spectral response curves obtained based on different bias voltages can be used to compare and reconstruct with the spectral response curves obtained through training, so as to finally achieve spectral data reconstruction. Furthermore, we fabricate a single spectrometer (that is, a single-pixel spectral image formed by a single cascaded photodiode device) into an array and connect them in series / parallel to achieve a one-time high-resolution spectral imaging function. The realization of this function lays a foundation for high-efficiency, low-cost, rapid spectral analysis and spectral imaging.

[0025] A reconfigurable spectrometer utilizes a photodetector that has a light response to a wide spectrum and this detector has different spectral response characteristics to different incident spectra, and combines with a superior algorithm to achieve the reconstruction of spectral signals and images; a spectral imager is an instrument that combines the functions of spectral imaging and spectral analysis. It can simultaneously obtain the spatial information (position, shape, etc.) and spectral information (optical characteristics of materials) of the object to be detected. Different from traditional spectrometers (which can only measure the single spectral information of incident light), a spectral imager can obtain the spectral data of the entire scene within the entire spatial range where the incident light is located, so it can be used to identify and distinguish different materials or substances and their spatial positions and distribution information.

[0026] Traditional spectrometers decompose light according to wavelength through dispersive elements (such as gratings and prisms) to measure spectral information. Its core principle is: using a dispersive element to separate the incident light by wavelength, and then recording the light intensity distribution of different wavelengths through a detector. Its disadvantages include: a) It requires multiple optical elements such as gratings, prisms, collimating lenses, and long-path optical systems, resulting in a large device volume and limitations; b) It relies on mechanical moving components (such as grating rotation and slit scanning) to cover the entire spectral range, which increases the measurement time; c) The mechanical scanning system not only has a slow response but is also vulnerable to mechanical errors, leading to reduced reliability and possible misalignment due to vibration or external environmental influences; d) It is not suitable for real-time spectral imaging. Traditional spectrometers usually obtain single-point or single-line spectra. To obtain spectral information of a large-area sample, point-by-point scanning or line scanning is required, resulting in a slow measurement speed.

[0027] Non-dispersive spectrometers do not rely on gratings or prisms for dispersion. Instead, they use methods such as narrowband filter arrays, Fourier transform spectroscopy, and dispersive optical devices (metasurfaces) to decompose the light source to be measured into different wavelength components and finally guide them to a photodetector for spectral measurement. Its disadvantages include: a) This approach is basically based on the architecture of "optical element" + "detector", and the entire spectrometer system is still very complex, with high requirements for packaging and application scenario stability; b) For spectrometers with narrowband filter arrays, a set of narrowband filters with fixed wavelengths is required to directly separate light in different bands and project it onto multiple detector pixels, which will limit the image resolution in imaging; c) The Fourier transform spectroscopy method requires a complex interference system, is sensitive to vibration, and has a very high computational complexity; d) Metasurface spectrometers use sub-wavelength structures to manipulate the propagation and dispersion of light to achieve ultra-compact and planar spectral measurement. Metasurfaces and their interactions with light rely on nanoscale structures, and their photon conversion efficiency is usually low, resulting in a decrease in the signal-to-noise ratio (SNR) of the spectrometer. Material absorption, scattering losses, and process defects of the structure will further reduce the light flux and affect the measurement accuracy.

[0028] A micro-computational spectrometer based on a photodetector with adjustable broadband spectral response obtains non-directly resolved spectral information through broadband photodetectors and combines advanced computational reconstruction algorithms to restore spectral data. The specific steps for spectral testing include: First, use a set of photodetectors with different responses to different spectra, such as nanowire arrays, metasurfaces, or multi-layer heterojunctions, to achieve selective absorption of signals at different wavelengths. Second, based on mathematical optimization and computational imaging techniques (such as compressive sensing, deep learning), reconstruct complete spectral information from the detected signals. The advantages of this method include: small device size, which can be integrated into chip level; suitable for flexible and programmable spectral measurement; no mechanical moving parts in spectral measurement, with high stability. Currently, the relevant representative research work in this field includes:

[0029] (1) Spatially compositional gradient nanowires (Yang, Zongyin, et al. "Single-nanowire spectrometers." Science 365.6457 (2019): 1017-1020.).

[0030] Principle: By forming different chemical composition distributions inside the nanowires. Different positions inside the nanowires have specific response characteristics to light of different wavelengths. Thus, selective response to light of different wavelengths is achieved.

[0031] Disadvantages: 1) This technical solution requires growing nanowires with a uniform lateral distribution of components, which has high requirements for the growth process; 2) It is necessary to fabricate a high-precision periodic electrode structure at the scale of dozens of nanometers, which has extremely high requirements for semiconductor processes; 3) It is difficult to fabricate array-level products. In spectral imaging, mechanical scanning needs to be used and it cannot be imaged at one time, so the application potential is not great; 4) It is difficult to grow nanowires with a spatially compositional distribution of large bandwidth response in a large scale range (the response range of this work is 500 - 700 nm, and the nanowires have reached dozens of micrometers). Therefore, it is very difficult to achieve a wide spectral resolution computational spectrometer using this technical solution.

[0032] (2) Colored silicon nanowire arrays (J. Meng, et al., "Detector-only spectrometer based on structurally colored silicon nanowires and a reconstruction algorithm." Nano Letters 20.1 (2019): 320-328.).

[0033] Principle: By means of the structural dispersion effect of the silicon nanowire array, the spectral response characteristics are regulated to achieve the detection of spectral information.

[0034] Disadvantages: 1) This technical solution requires the growth of nanowire arrays with different nanoscale periodic distributions, which has relatively high requirements for the growth and fabrication processes; 2) The resolution of the spectrometer prepared by this technical solution depends on the number of types of nanowire arrays with different periodic distributions. To achieve a high-precision spectrometer, a large number of array pixel units need to be fabricated, which limits its miniaturization. 3) Due to the relatively high requirements for the process, a large number of pixel units are required for a single spectrometer. Therefore, for spectral imaging application scenarios, it is difficult to be arrayed and cannot meet the requirements for spectral imaging in real-life scenarios. 4) For short wavelengths (such as the ultraviolet band), nanowire periodic arrays with smaller sizes need to be fabricated, and the fabrication difficulty and cost increase geometrically.

[0035] (3) Filter-encoded photodetector array (J. Bao, et al., "A colloidal quantum dot spectrometer." Nature 523.7558 (2015): 67-70.).

[0036] Principle: By integrating different wavelength-selective filters (such as different colloidal quantum dots) on the surface of the photodetector, the spectral resolution is improved.

[0037] Disadvantages: 1) This technical solution requires the integration of colloidal quantum dots with different shapes, types, and thicknesses, which has relatively high requirements for the fabrication process; 2) The preparation of colloidal quantum dots has a large randomness, and it is difficult to ensure the uniformity of the preparation in different batches, which is difficult for large-scale production. 3) The resolution of the spectrometer prepared by this technical solution depends on the number of colloidal quantum dot arrays, which limits its miniaturization and arraying process. 4) For short wavelengths (such as the ultraviolet band), it is difficult to find colloidal quantum dots in this band, and there is no application scenario with wide spectral resolution.

[0038] (4) Two-dimensional material-based photodetectors with tunable bandgaps (S. Yuan, et al. "A wavelength-scale black phosphorus spectrometer." Nature Photonics 15.8 (2021): 601-607; H. Yoon, et al. "Miniaturized spectrometers with a tunable van der Waals junction." Science 378.6617 (2022): 296-299.).

[0039] Principle: By applying an electric field to regulate the energy band structure of two-dimensional materials, their bandgaps can be adjusted, thereby dynamically adjusting the spectral response range.

[0040] Disadvantages: 1) Limited linear dynamic range: The photoabsorption layer of two-dimensional materials is usually very thin (only a few nanometers), and the number of photo-generated carriers is small, resulting in a limited linear dynamic range (LDR) of the detector. This may cause signal saturation under strong light conditions and weak signals under weak light conditions, affecting the accuracy of spectral data. 2) Poor material uniformity and repeatability, and difficult to mass-produce in arrays: Currently, the preparation methods of two-dimensional materials (such as CVD, mechanical exfoliation) may lead to poor material uniformity, such as uneven thickness, grain boundary defects, uneven doping, etc. 3) Limited spectral coverage: A single type of two-dimensional material has a specific bandgap range and is difficult to cover the broad spectral range from ultraviolet to infrared. It is necessary to expand the spectral response through composite structures or hybrid detectors, increasing the instability of the system.

[0041] Based on the current situation of the above-mentioned existing technologies, the present disclosure proposes an on-chip integrated micro-spectrometer based on an optoelectronic cascaded diode epitaxial structure, which can be, for example, an n-i-p diode with a wide spectral response at the bottom of the cascade and a p-i-n diode with a narrow spectral response at the top. Working principle of the on-chip integrated micro-computing spectrometer based on the optoelectronic cascaded diode epitaxial structure: First, the bottom n-i-p diode has a wide spectral response and can generate a fixed photocurrent response to light of different wavelengths; second, the top p-i-n diode has a narrow spectral response to light and generates a photocurrent response in the opposite direction to the bottom diode. Since the two optoelectronic cascaded diodes generate opposite photocurrents, a photocurrent competition mechanism is generated. Under different bias conditions, the energy band offset trend of the two diodes will change, thereby changing the intensity and characteristics of the photocurrent competition and resulting in an adjustable spectral response curve. Finally, through spectral reconstruction methods, such as deep neural network modeling based on the device current-voltage (I-V) curve data, 1. First, the device response obtained through I-V measurement is used as the input signal, which is processed by a large number of neurons and captures its non-linear characteristics through an activation function. 2. A residual block containing three wide connection layers is used to effectively prevent gradient disappearance, thereby extracting deeper feature information. 3. The output layer converts the processed data into the final spectral information. For example, the entire model can be trained in batches on a GPU, with an initial learning rate of , after hundreds of iterations, weight decay is performed and finally convergence is achieved. Through this method, the deep neural network can accurately learn the complex mapping relationship between the device I-V curve and the spectrum, and achieve high-precision spectrum reconstruction. Thus, based on the spectral response curves under different bias voltages, the reconstruction of spectral data and images can be realized. In addition, a functional layer (such as two-dimensional materials, photonic crystal layers, metasurfaces, gratings, etc.) that can modulate the optical information (wavelength, optical power, light polarization, light phase) of the incident light can be further integrated on the back or top of the substrate of the photodiode. While achieving the technical effect of spectrum reconstruction, the application prospects can be expanded.

[0042] To make the objectives, technical solutions, and advantages of the present disclosure clearer and more understandable, the following further describes the present disclosure in detail with reference to specific embodiments and the accompanying drawings.

[0043] In an embodiment of the present disclosure, a chip-integrated micro-spectrometer based on a photoelectric cascade diode epitaxial structure is provided. Combining Figure 1 and Figure 2 As shown, the chip-integrated micro-spectrometer includes a substrate, a photoelectric cascade diode epitaxial structure located on the substrate, and electrodes; wherein, the photodiode epitaxial structure includes at least two vertically cascaded photodiodes. Each photodiode can be used as a photodetector to generate spectral responses for spectra in different spectral ranges respectively, so that the spectral response curve of each photodiode can be adjusted with the change of the incident light spectral information and / or the external bias voltage. Since it is realized based on a semiconductor epitaxial structure, the size of the micro-spectrometer can be minimized to the nanoscale, or a micro-spectrometer with a micron-scale or larger size (inch-scale) can be prepared according to requirements.

[0044] According to an embodiment of the present disclosure, the photoelectric cascade diode epitaxial structure at least includes a first photodiode and a second photodiode stacked in sequence on the substrate. The first photodiode is used as the first photodetector to generate a spectral response for the spectrum in the first spectral range. For example, the response wavelength of the first spectral range is λ1, 10 nm ≤ λ1 ≤ 10000 nm, that is, the optical wavelength of the incident light falls within this wavelength range; the second photodiode is used as the second photodetector to generate spectral responses for spectral intervals different from the first spectral range within the working wavelength range of the on-chip micro-spectrometer. As Figure 2 shown, the photoelectric cascade diode epitaxial structure includes four photodiode epitaxial structures stacked in sequence in the vertical direction.

[0045] According to an embodiment of the present disclosure, as Figure 1As shown, the optoelectronic cascade diode epitaxial structure includes, from bottom to top: a substrate 1, an epitaxial buffer layer 2, a first N-type semiconductor material layer 3, a first undoped semiconductor material layer 4, a P-type semiconductor material layer 5, a second undoped semiconductor material layer 6, and a second N-type semiconductor material layer 7.

[0046] Among them, the first undoped semiconductor material layer (4) is formed on a part of the first N-type semiconductor material layer 3, and a first electrode 8 is prepared on another part of the first N-type semiconductor material layer 3; a second electrode 9 is provided on the surface of the second N-type semiconductor material layer 7. Among them, the first N-type semiconductor material layer 3, the first undoped semiconductor material layer 4, and the P-type semiconductor material layer 5 constitute an n-i-p type bottom diode structure (i.e., the first photodiode), which serves as a first photodetector with a first spectral response. The P-type semiconductor material layer 5, the second undoped semiconductor material layer 6, and the second N-type semiconductor material layer 7 constitute a p-i-n type top diode structure (i.e., the second photodiode), which serves as a second photodetector with a second spectral response, thereby realizing a micro spectrometer based on the optoelectronic cascade diode epitaxial structure. Among them, i (intrinsic) in the n-i-p or p-i-n layer represents an intrinsic epitaxial layer. The material in the intrinsic epitaxial layer (corresponding to the first and second undoped semiconductor material layers 4 and 6) can be a material with a fixed composition, a material with a gradually changing composition, or a material with a stepwise change. The way of composition change can be gradual increase; gradual decrease; increase first and then decrease; decrease first and then increase; or non-linear increase and decrease, etc. In this optoelectronic cascade diode epitaxial structure, for the other epitaxial layers except the intrinsic layer, the composition of each layer can be fixed or gradually changing. Among them, the thickness of each gradient layer ranges from 0.1 nm to 5 μm. The way of composition gradient (how fast the composition changes with thickness) will only change the specific photocurrent response performance, spectral resolution ability and accuracy of the cascade photodiode, but can all meet the requirements for realizing a micro spectrometer (that is, the response of the cascade photodiode to light of a specific wavelength changes with the bias voltage).

[0047] According to the embodiments of the present disclosure, the material compositions of the first undoped semiconductor material layer (4) and the second undoped semiconductor material layer (6) are different, so that the spectral response coverage of the first photodiode is different from that of the second photodiode; the spectral response range of the on-chip integrated micro-spectrometer covers a wide spectral range from deep ultraviolet to infrared within the wavelength range of 10 nm - 10000 nm. The material parameters of the first undoped semiconductor material layer 4 and the second undoped semiconductor material layer 6 are different, so that the spectral response ranges of the first spectral response and the second spectral response are different. It should also be noted that the first undoped semiconductor material layer (4) and the second undoped semiconductor material layer (6) are preferably selected as undoped semiconductor materials. Actually, these two material layers can also be doped according to actual situations to achieve different spectral response ranges and response accuracies, or technical effects such as similar bias-adjustable light responses.

[0048] According to an embodiment of the present disclosure, for example, a bottom diode structure located on a substrate serves as a photodetector with broadband spectral response, and a top diode structure serves as a photodetector with narrowband spectral response, forming a back-to-back optoelectronic cascaded diode epitaxial architecture. The bottom diode structure and the top diode structure generate photocurrent responses in opposite directions under the action of light with different wavelengths. Under different bias conditions, the band offset trend of the bottom diode and / or the top diode changes, thereby changing the intensity and characteristics of photocurrent competition, making the response curves of the first spectral response and / or the second spectral response adjustable. The material for preparing the substrate is selected from compound semiconductors including sapphire, silicon, germanium, silicon carbide, gallium oxide, boron nitride, diamond, aluminum nitride, gallium nitride, gallium arsenide, indium phosphide, or quartz glass or a substrate material that is transparent to light in the spectral range from deep ultraviolet light to infrared light; the material for preparing the first electrode and / or the second electrode is selected from Ti, Al, Ni, Au, Cr, Pt, or their combinations. The material for preparing the optoelectronic cascaded diode epitaxial structure is selected from binary, ternary, or quaternary metal nitrides of Ga, Al, In, or binary, ternary, or quaternary metal phosphides of Ga, Al, In, or binary, ternary, or quaternary metal arsenides of Ga, Al, In, or binary, ternary, or quaternary metal antimonides of Ga, Al, In; for example, the material for preparing one or more of the buffer layer 2, the first N-type semiconductor material layer 3, the first undoped semiconductor material layer 4, the P-type semiconductor material layer 5, the second undoped semiconductor material layer 6, and the second N-type semiconductor material layer 7 that make up the epitaxial structure or epitaxial film is selected from GaN, AlN, InN, GaAs, AlAs, InAs, or GaP, AlP, InP, or AlSb, GaSb, InSb; the material for preparing the first N-type semiconductor material layer (3) and / or the P-type semiconductor material layer (5) and / or the second N-type semiconductor material layer (7) is selected from materials with corresponding fixed components or materials with gradually changing components or materials with stepwise changes or non-linear increase or decrease changes in components among the above materials, and other epitaxial layers can also be materials with fixed components or changing components. The thickness of each layer in the optoelectronic cascaded diode epitaxial structure ranges from 0.1 nm to 5 μm. It should be noted that by changing the component distribution and component composition form of each layer of material in the optoelectronic cascaded diode, their light absorption performance can be changed, such as a compositionally graded layer achieving light absorption in a broad spectral range. Specifically, during the epitaxial growth of the material, along the epitaxial direction, by gradually changing the components of the material, materials with different components correspond to absorbing the wavelength range corresponding to that material, generating a certain amount of photo-generated electrons and hole pairs, and finally achieving a photocurrent response curve for a specific spectrum, providing a device basis for subsequent spectral reconstruction.

[0049] It should be noted that the miniature spectrometer based on the optoelectronic cascaded diode epitaxial structure of the present disclosure includes at least two cascaded bottom diode structures and top diode structures, that is, a group of optoelectronic cascaded diode epitaxial structures, such as Figure 2 shown. For example, the bottommost is an n-i-p type diode, and the upper one is a p-i-n type diode, and stacking can continue, such as Figure 2 shown. An n-i-p type diode and a p-i-n type diode are further fabricated on the p-i-n type diode in the first group of optoelectronic cascaded diodes to form a second group of cascaded n-i-p type / and p-i-n type diode structures. According to actual requirements, the third group and fourth group of optoelectronic cascaded diode epitaxial structures can continue to be stacked. It should be noted that the stacking order of the n-i-p type diode and the p-i-n type diode can be reversed or changed. In addition, different light responses can also be exhibited under different bias voltages based on one n-i-p type diode or p-i-n type diode, so as to construct a miniature spectrometer, such as inserting a tunneling junction structure in a single diode. The tunneling junction can be inserted into any layer of this optoelectronic cascaded diode or at the connection between any two layers. The thickness of the tunneling junction is between 0.1 and 500 nm. The material composition of the tunneling junction is similar to that of the surrounding material elements, but the proportion of the surrounding material components is different. Preferably, the miniature spectrometer based on two optoelectronic cascaded diode epitaxial structures will be mainly described, such as Figure 1 shown. An AlN buffer layer, an n-type doped Al 0.6 Ga 0.4 N layer, a gradient unintentionally doped compositionally graded layer Al 0.6-0 Ga 0.4-1 N are sequentially grown on a sapphire substrate, and a p-type doped GaN layer is grown above. Finally, an unintentionally doped GaN layer and an n-type doped GaN layer are grown on the top layer. The gradient unintentionally doped compositionally graded layer is the reason for the bottom diode to achieve broadband spectral response. It should be noted that the thickness of each layer in the epitaxial structure is between 0.1 nm and 5 μm. Any change in thickness does not affect the effect. In addition, the unintentionally doped layer in the optoelectronic cascaded diode epitaxial structure can also be n-type or p-type doped, and the doping concentration ranges from the completely undoped case to the electron concentration in the n-type doped Al 0.6 Ga 0.4 N layer or the hole concentration in the p-type doped GaN layer.

[0050] It should be noted that due to the mutual cascading of two or several photodiodes, in the case of applying positive or negative voltage to the photonic cascaded diode, there is always one or several photodiodes operating in one of the forward and reverse bias states, that is, at least one photodiode in this cascaded photodiode operates in the forward bias state and at least one photodiode operates in the reverse bias state. As a result, the leakage current of the photonic cascaded diode is extremely low, which has significant advantages in terms of device stability and energy consumption, and is also beneficial to improving the spectral measurement and spectral resolution ability (i.e., spectral resolution) of the spectrometer. According to the embodiments of the present disclosure, as Figure 5 shown, the on-chip micro-spectrometer further includes functional layers located at the top or bottom that can further integrate functions for regulating the optical information of the incident light, such as functional layer 11 located at the top and functional layer 10 located at the bottom. The optical information includes wavelength, optical power, light polarization, and light phase.

[0051] According to the embodiments of the present disclosure, the implementation methods of the epitaxial structure of the photonic cascaded diode include: realizing through epitaxial growth of materials, realizing through physical transfer, realizing through mechanical exfoliation, and realizing through van der Waals contact based on low-dimensional materials.

[0052] According to the embodiments of the present disclosure, the cross-sectional area of the on-chip integrated micro-spectrometer or the photonic cascaded diode device in the vertical screen direction is 1 nm 2 - 1000 mm 2 , and the cross-sectional shape includes: circular, rectangular, regular polygon or irregular shape. The structure of the photonic cascaded diode can be a thin film structure, a nanowire structure, a nanorod structure and other irregular structures.

[0053] On the other hand, the present disclosure also provides a spectral imager based on the above-mentioned on-chip integrated micro-spectrometer array, wherein the control mode of the micro-spectrometer array is that each micro-spectrometer unit is individually controlled by an external circuit, or multiple micro-spectrometer units are controlled in a parallel, series, or series-parallel combination manner to achieve a wide spectral working range from deep ultraviolet to infrared, so as to realize spectral detection, spectral analysis, and spectral imaging of wide-spectrum incident light.

[0054] It should be noted that the on-chip micro-spectrometer and spectral imager of the present disclosure do not rely on specific epitaxial materials, and arsenides, III-V, and II-IV groups can all be realized based on the cascaded diode epitaxial structure.

[0055] The preparation method of the above-mentioned on-chip integrated micro-spectrometer based on the epitaxial structure of the photonic cascaded diode includes:

[0056] (1)Epitaxially grow buffer layer 2, first N-type semiconductor material layer 3, first undoped semiconductor material layer 4, P-type semiconductor material layer 5, second undoped semiconductor material layer 6, second N-type semiconductor material layer 7 and other thin film structures on the substrate. According to actual process requirements, the epitaxial structure can be prepared as a thin film, or in the form of nanocolumns, nanowires or other types.

[0057] (2)Etch the epitaxial wafer obtained in step (1) using photolithography and dry etching processes, so that the surface of the first N-type semiconductor material layer 3 is exposed.

[0058] (3)Fabricate the first electrode 8 on the surface of the exposed first N-type semiconductor material layer of the product obtained in step (2) through photolithography, evaporation and annealing processes. The first electrode 8 is a multi-metal of Ti / Al / Ti / Au, Ti / Au, Ti / Al / Ni / Au, Cr / Au or Cr / Al / Ti / Au.

[0059] (4)Fabricate the second electrode 9 on the surface of the exposed second N-type semiconductor material layer of the product obtained in step (3) through photolithography, evaporation and annealing processes. The second electrode 9 is a multi-metal of Ti / Al / Ti / Au, Ti / Au, Ti / Al / Ni / Au, Cr / Au or Cr / Al / Ti / Au.

[0060] It should be noted that during the preparation process, changes in the etching mesa inclination, size, electrode pattern design, and epitaxial structure of the semiconductor epitaxial device do not deviate from the technical concept of the present disclosure and do not affect the final effect of the micro-spectroscopic device. As Figure 3 shown, the working range of the on-chip integrated micro-spectrometer using a cascade diode epitaxial structure can reach 250 - 700 nm, which is a technical effect never achieved by existing micro-spectroscopic devices. In addition, as Figure 4 shown, by optimizing the materials (such as materials, components), the working range of the miniaturized spectrometer using a photoelectric cascade diode epitaxial structure can reach 200 - 10000 nm, and based on Figure 4For the material system shown, through the electronic transition of the inner shell layer, the working range of the miniaturized spectrometer can be extended to the X-ray and extreme ultraviolet bands. That is to say, by changing the material and the material response mechanism, the working range of the miniaturized spectrometer using the optoelectronic cascade diode epitaxial structure can achieve a spectral range of 10 - 10000 nm. In addition, the wavelength resolution accuracy of the miniaturized spectrometer of the present disclosure can reach 0.62 nm. By optimizing the number of cascade diodes in the optoelectronic cascade diode, the thickness of each layer of material in the optoelectronic cascade diode, the composition of each layer of material, and the change trend of the composition of each layer of material along the material epitaxial growth direction, including the rate of change of the material composition per unit thickness, the change direction (gradual decrease or increase of a specific element), and the doping situation, the wavelength resolution accuracy can be improved to the picometer level. In addition, the resolution accuracy of the spectrometer of the present disclosure can be accurately adjusted according to actual needs.

[0061] In addition, as Figure 6 shown, it is compatible with the focal plane array preparation process, and an array-level spectrometer product can be prepared, realizing a miniaturized integrated spectral imager.

[0062] The on-chip integrated miniaturized spectrometer and spectral imager based on the optoelectronic cascade diode epitaxial structure of the present disclosure have the following beneficial effects:

[0063] (1) Realize the simplification of the miniaturized spectrometer: This on-chip miniaturized spectrometer relies on different light response behaviors under different voltage drives to perform spectral reconstruction. Therefore, a single on-chip miniaturized spectrometer device can complete the function of spectral reconstruction.

[0064] (2) Higher response efficiency: The different light response behaviors generated by this miniaturized spectrometer are essentially composed of at least two photodetectors with different response ranges and opposite directions in cascade. Its photocurrent all comes from its unintentionally doped active region. Therefore, the light response efficiency of the photodetector can be guaranteed at a relatively high level.

[0065] (3) Realize the miniaturization of the miniaturized spectrometer: The on-chip miniaturized spectrometer of the present disclosure is designed based on a vertical epitaxial structure. Therefore, the physical size of the device does not affect the function of spectral reconstruction. Theoretically, within the range allowed by semiconductor processes, a miniaturized spectrometer with any size from 1 nm 2 - 1000 mm 2 can be realized, and a nanoscale miniaturized spectrometer can be achieved.

[0066] (4) Realize the array and large-scale production of the miniaturized spectrometer: It is manufactured using standard III-V semiconductor processes, has the ability of large-scale production and integration, and a two-inch wafer-level product demonstration has been carried out.

[0067] (5) Realization of a miniaturized on-chip spectral imager: The fabrication process is compatible with the fabrication process of the focal plane array. Therefore, an array-level spectrometer product is fabricated, realizing a miniaturized integrated spectral imager.

[0068] (6) Realization of a wide-spectrum miniaturized on-chip spectral imager: It only requires at least cascading photodetectors with wide-spectrum response at the bottom and photodetectors with narrow-spectrum response at the top to form an architecture. Therefore, III-V semiconductor material systems (the response wavelength range corresponding to the bandgap of this material system covers ultraviolet to infrared) can be used to achieve a wide spectrum from deep ultraviolet to infrared.

[0069] So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that in the accompanying drawings or the text of the specification, the implementation manners that are not depicted or described are all forms known to those of ordinary skill in the art and are not described in detail. In addition, the definitions of the above-mentioned various elements and methods are not limited to the specific structures, shapes, or manners mentioned in the embodiments, and those of ordinary skill in the art can simply modify or replace them.

[0070] In addition, in this article, except as specifically indicated, ordinal numbers such as "first", "second", etc. are only used to distinguish multiple elements with the same name and do not indicate the existence of a rank, level, execution order, or process order between them. A "first" element and a "second" element may appear in the same component together or in different components separately. The existence of an element with a larger ordinal number does not necessarily mean the existence of another element with a smaller ordinal number.

[0071] In this article, except as specifically indicated, the so-called feature A "or" (or) or "and / or" (and / or) feature B means that A exists alone, B exists alone, or A and B exist simultaneously; the so-called feature A "and" (and) or "and" (and) or "and" (and) feature B means that A and B exist simultaneously; the so-called "include", "contain", "have", "contain" means including but not limited to this.

[0072] In addition, in this article, terms such as "above", "below", "left", "right", "front", "rear", or "between" are only used to describe the relative positions between multiple elements and can be extended in interpretation to include translation, rotation, or mirroring situations. In addition, in this article, except as specifically indicated, the statement that "one element is on another element" or similar does not necessarily mean that the element contacts the other element.

[0073] In addition, unless specifically described or steps that must occur in sequence, the order of the above steps is not limited to those listed above and can be varied or rearranged according to the required design. And based on considerations of design and reliability, the above embodiments can be used in combination with each other or in combination with other embodiments, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0074] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not used to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. An on-chip integrated micro spectrometer based on a cascaded diode epitaxial structure, comprising a substrate, a photoelectric cascaded diode epitaxial structure located on the substrate, and an electrode; Among them, The photoelectric cascaded diode epitaxial structure includes at least two vertically cascaded photodiodes. Each photodiode, as a photodetector, can generate spectral responses for spectra in different spectral ranges respectively, such that the spectral response curve of each photodiode can be adjusted with the change of incident light spectral information and / or external bias voltage, realizing high-precision spectral measurement, analysis, and spectral imaging.

2. The on-chip integrated micro spectrometer according to claim 1, wherein: The photoelectric cascaded diode epitaxial structure at least includes a first photodiode and a second photodiode stacked in sequence from above the substrate; The first photodiode, as the first photodetector, generates a spectral response for the spectrum in the first spectral range. The response wavelength of the first spectral range is λ1, where 10 nm ≤ λ1 ≤ 10000 nm, that is, the first response spectral range is within 10 nm to 10 μm; The second spectral range of the second photodiode, as the second photodetector, is different from the first spectral range.

3. The on-chip integrated micro spectrometer according to claim 2, wherein: The photoelectric cascaded diode epitaxial structure at least includes, from bottom to top: a first N-type semiconductor material layer (3), a first undoped semiconductor material layer (4), a P-type semiconductor material layer (5), a second undoped semiconductor material layer (6), and a second N-type semiconductor material layer (7); The first N-type semiconductor material layer (3), the first undoped semiconductor material layer (4), and the P-type semiconductor material layer (5) constitute the first photodiode; the P-type semiconductor material layer (5), the second undoped semiconductor material layer (6), and the second N-type semiconductor material layer (7) constitute the second photodiode.

4. For the on-chip integrated micro spectrometer according to claim 3, the material compositions of the first undoped semiconductor material layer (4) and the second undoped semiconductor material layer (6) are different, so that the coverage ranges of the spectral responses of the first photodiode and the second photodiode are different; the spectral response range of the on-chip integrated micro spectrometer covers the spectral range from 10 nm to 10000 nm and the spectral ranges within this range.

5. The on-chip integrated micro spectrometer according to claim 1 further includes a functional layer that can be further integrated on the top of the photoelectric cascaded diode or at the bottom of the substrate and can regulate the optical information of the incident light. The optical information includes wavelength, optical power, light polarization, and light phase.

6. The on-chip integrated micro spectrometer according to claim 1, wherein: The cross-sectional area of the optoelectronic cascade diode device in the horizontal direction is 1 nm 2 -1000 mm 2 , and the cross-sectional shape includes: circular, rectangular, regular polygon or irregular shape; The photoelectric cascaded diode structure can be a thin film structure, a nanowire structure, a nanorod structure, and other irregular structures.

7. The on-chip micro-spectrometer according to claim 1, wherein the implementation method of the optoelectronic cascaded diode epitaxial structure includes: Realized by epitaxial growth of materials, realized by physical transfer, realized by mechanical exfoliation, and realized by van der Waals contact based on low-dimensional materials.

8. The on-chip integrated micro spectrometer according to claim 1, wherein: The preparation material of the substrate is selected from semiconductors including sapphire, silicon, germanium, silicon carbide, gallium oxide, boron nitride, diamond, aluminum nitride, gallium nitride, gallium arsenide, indium phosphide, or quartz glass, or materials that are transparent to light in the wavelength range from deep ultraviolet light to infrared light; The preparation material of the electrode is selected from Ti, Al, Ni, Au, Cr, Pt, or their combinations.

9. The on-chip integrated micro-spectrometer according to claim 3, wherein: The preparation material of each layer in the optoelectronic cascaded diode epitaxial structure is selected from binary, ternary, or quaternary metal nitrides of Ga, Al, In, or binary, ternary, or quaternary metal phosphides of Ga, Al, In, or binary, ternary, or quaternary metal arsenides of Ga, Al, In, or binary, ternary, or quaternary metal antimonides of Ga, Al, In; The material of each layer in the optoelectronic cascaded diode epitaxial structure is selected from materials with fixed components, or materials with gradually changing components, or materials with stepped changes or non-linear increase or decrease changes among the corresponding materials in the same family as described above; The thickness of each layer in the optoelectronic cascaded diode epitaxial structure ranges from 0.1 nm to 5 μm.

10. A spectral imager based on the on-chip integrated micro-spectrometer array according to any one of claims 1-9, wherein the control mode of the micro-spectrometer array is that each micro-spectrometer unit is individually controlled by an external circuit, or multiple micro-spectrometer units are controlled in parallel, series, or a combination of series and parallel to achieve high-precision spectral detection, spectral analysis, and spectral imaging of incident light in a wide spectrum.

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