A tunneling photodiode with bias voltage-controlled dynamic range, its preparation method and application

Abstract

The present invention provides a tunneling photodiode with bias-controlled dynamic range, and its preparation method and application, which belong to the field of photodiode technology. The diode includes a conductive substrate, a first light-absorbing layer, a tunneling layer, a second light-absorbing layer and a metal electrode stacked in sequence from bottom to top; the first light-absorbing layer and the second light-absorbing layer form an I-type energy band heterojunction. The present invention constructs a tunneling photodiode by introducing an extremely thin tunneling layer at the interface of the I-type heterojunction, thereby achieving continuous and rapid adjustment of the dynamic range of the tunneling photodiode by adjusting the external bias, so that it can adapt to different lighting conditions. Under positive bias, the device has high gain and is suitable for strong light detection; under reverse bias, the device gain is reduced to avoid saturation effect under strong light, and is suitable for medium-strong light detection; under zero bias, the device has extremely low dark current, and the optimized signal-to-noise ratio improves the sensitivity of weak light detection, and is suitable for weak light detection, thereby achieving a high dynamic range.

Description

Technical Field

[0001] The present invention belongs to the technical field of photodiodes, and in particular relates to a tunneling photodiode with bias voltage regulating dynamic range, a preparation method thereof, and applications thereof. Background Art

[0002] With technological advancements, the performance requirements for photodetectors are becoming increasingly stringent, particularly in terms of dynamic range, response speed, and low-light detection capabilities. Adjustable dynamic range can avoid the overexposure or loss of detail in dark areas caused by a fixed dynamic range, allowing the detector to adjust its sensitivity in real time and retain more effective information. Traditional photodiodes, such as PIN photodiodes, while offering excellent performance, have dynamic ranges that are typically determined by the inherent properties of the material and device structure, making them difficult to flexibly adjust through external means. The paper (Yang, Sung-Hyun, and Kyoung-Rok Cho. High dynamic range CMOS image sensor with conditional reset. Proceedings of the IEEE 2002 Custom Integrated Circuits Conference (Cat. No. 02CH37285). IEEE, 2002.) notes that traditional PIN photodiodes have limitations in dynamic range adjustment, making them difficult to meet the requirements of high dynamic range imaging. The literature (Bandoh, Yukihiro, et al. Recent advances in highdynamic range imaging technology. 2010 IEEE International Conference on ImageProcessing. IEEE, 2010.) points out that traditional photodetectors still need to be improved in terms of dynamic range and low-light detection capabilities.

[0003] Tunnel photodiodes utilize the quantum tunneling effect, offering advantages such as high-speed response and low noise, and have potential applications in high-frequency optical communications and rapid light detection. However, traditional tunnel photodiodes also suffer from a limited dynamic range, making it difficult to address both strong-light and weak-light detection requirements. Patent ZL201410818494.4 discloses an avalanche photodiode and a method for its fabrication, noting that tunnel photodiodes have high-speed response characteristics but are deficient in dynamic range. Patent ZL201510098629.9 discloses a resonant tunnel diode with low dark current and high sensitivity, noting that tunnel photodiodes have potential for application in weak-light detection, but that the dynamic range needs to be further optimized.

[0004] To address these issues, researchers have developed a variety of technologies to extend the dynamic range of photodiodes, such as using nonlinear resistive materials and multi-level gain structures. The papers (Huang, Y., Guan, Z., Dai, X. et al. Engineered macrophages as near-infrared light activated drug vectors forchemo-photodynamic therapy of primary and bone metastatic breast cancer. Nat Commun 12, 4310 (2021).) and (Le Gallo, M., Khaddam-Aljameh, R., Stanisavljevic,M. et al. A 64-core mixed-signal in-memory compute chip based on phase-change memory for deep neural network inference. Nat Electron 6, 680–693 (2023).) state that the dynamic range and weak-light detection capabilities of photodiodes can be significantly improved through interface engineering and novel device structure design. Research results on optimizing dynamic range and quantum efficiency using guided-mode resonance structures are reported in the paper (JN Kirchhof, Y. Yu, G. Antheaume, G. Gordeev, D. Yagodkin, P. Elliott, et al. Nanomechanical Spectroscopy of 2D Materials. Nano Letters. 22, 8037-8044 (2022).) However, these approaches often increase device complexity and manufacturing costs, and make it difficult to achieve continuous and precise adjustment of the dynamic range.

[0005] Therefore, how to design tunneling photodiodes so that they can cover an ultra-wide dynamic range from weak light to strong light through simple adjustment has become a research focus. Summary of the Invention

[0006] To address the challenges presented by the prior art, the present invention aims to provide a tunneling photodiode with bias-controlled dynamic range, as well as its preparation method and application. By selecting specific materials to construct the diode structure, this diode exhibits a wide dynamic range. This dynamic range can be adjusted simply by applying a bias voltage, improving the device's detection performance in both low-light and high-light conditions.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A tunneling photodiode with bias voltage-controlled dynamic range comprises a conductive substrate, a first light absorption layer, a tunneling layer, a second light absorption layer, and a metal electrode stacked in sequence from bottom to top;

[0009] The first light absorbing layer and the second light absorbing layer form an I-type energy band heterojunction;

[0010] The metal electrode is a patterned electrode, and the metal electrode does not completely cover the second light absorption layer.

[0011] Furthermore, the material of the first light absorption layer and the material of the second light absorption layer are any one of silicon, germanium, gallium arsenide, lead telluride, lead sulfide, lead selenide, indium gallium arsenide, indium phosphide, and mercury cadmium telluride, and the material of the first light absorption layer and the material of the second light absorption layer are different, and the band gap width is also different.

[0012] Furthermore, the material of the tunneling layer is any one of aluminum oxide, zinc oxide, silicon oxide, silicon nitride, silver iodide, and indium gallium nitride.

[0013] Furthermore, the metal electrode is made of any one of gold, nickel, chromium, titanium, and aluminum, or an alloy of at least two of them; the conductive substrate material is ITO, silver film, copper, gold, aluminum, nickel, chromium, etc.

[0014] Furthermore, the thickness of the first light absorption layer is 0.2μm~500μm; the thickness of the tunneling layer is 1nm~10nm; the thickness of the second light absorption layer is 0.05μm~5μm. If the thickness is too thick, it may block some photons from reaching the first light absorption layer, reducing the overall absorption efficiency. If it is too thin, the light in its target band will not be fully absorbed, reducing the quantum efficiency.

[0015] Furthermore, the thickness of the metal electrode is 10 nm to 100 nm.

[0016] The present invention also provides a method for controlling the dynamic range of the tunneling photodiode, the specific process of which is as follows:

[0017] Applying a positive bias voltage, which should be greater than the threshold voltage for tunneling, results in a high gain device suitable for strong light detection.

[0018] When reverse bias is applied, the device gain is reduced, avoiding the saturation effect under strong light, which is suitable for medium-intensity light detection;

[0019] When zero bias is applied, the device has extremely low dark current, and the optimized signal-to-noise ratio improves the sensitivity of weak light detection, making it suitable for weak light detection.

[0020] A method for preparing a tunneling photodiode with bias voltage-controlled dynamic range comprises the following steps:

[0021] Step 1: preparing a first light-absorbing layer on a conductive substrate, wherein the conductive substrate serves as a bottom electrode;

[0022] Step 2: growing a tunneling layer on the first light absorbing layer;

[0023] Step 3: growing a second light absorbing layer on the tunneling layer;

[0024] Step 4: Deposit a metal electrode on the second light-absorbing layer as a top electrode.

[0025] Furthermore, the first light absorbing layer in step 1, the tunneling layer in step 2, and the second light absorbing layer in step 3 are prepared by any one of molecular beam epitaxy, atomic force deposition, metal organic chemical vapor deposition, magnetron sputtering, or thermal evaporation.

[0026] The present invention also provides applications of the tunneling photodiode in fields such as high dynamic range imaging and weak light detection.

[0027] The mechanism of the present invention is:

[0028] The first and second light-absorbing layers form an I-type bandgap heterojunction. Under a positive bias, the applied electric field is in the opposite direction of the built-in electric field, and the junction region formed by the heterojunction acts as a depletion layer. The thinning of the depletion layer, combined with the I-type junction structure, makes it easy for photogenerated electrons to undergo Fowler-Nordheim tunneling (FNT). The introduction of an extremely thin tunneling layer further increases the probability of electron tunneling. The barrier width of the extremely thin (nanometer-scale) tunneling layer is extremely small. At this time, applying a reverse bias can tilt the energy bands, further lowering the effective barrier. In other words, under reverse bias, the presence of the extremely thin tunneling layer makes it extremely easy for electrons to undergo direct tunneling. Different saturation currents are also observed at different bias voltages. The dark current of the photodiode is lowest at zero bias, and at this time, it has good detection sensitivity in low light conditions. In other words, different tunneling mechanisms under different bias voltages give heterojunction devices different dynamic ranges, ultimately achieving an ultra-wide dynamic range covering low light conditions to strong light conditions.

[0029] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] 1. This invention constructs a tunneling photodiode by introducing an extremely thin tunneling layer at the I-type heterojunction interface. This allows the dynamic range of the tunneling photodiode to be continuously and rapidly adjusted by adjusting the external bias voltage, enabling it to adapt to varying lighting conditions. Under forward bias, the device exhibits high gain, making it suitable for strong-light detection. Under reverse bias, the device gain is reduced, avoiding saturation effects under strong light and making it suitable for medium-to-strong light detection. Under zero bias, the device exhibits extremely low dark current, an optimized signal-to-noise ratio, and improved sensitivity for weak-light detection, thus achieving a high dynamic range.

[0031] 2. The present invention has a simple preparation process, low manufacturing cost, and is convenient for large-scale integration, and can be widely used in the fields of visible light and infrared detection and imaging technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the tunneling photodiode according to embodiment 1 of the present invention.

[0033] Figure 2 It is a schematic structural diagram of the metal electrode in the tunneling photodiode according to embodiment 1 of the present invention.

[0034] Figure 3 is the energy band diagram of the device in Example 1.

[0035] Figure 4 3 is a current-voltage characteristic curve of the device in Example 1 under zero bias in a dark environment.

[0036] Figure 5 is the dynamic range of the device in Example 1 under zero bias.

[0037] Figure 6 is the dynamic range of the device in Example 1 under reverse bias (-1V).

[0038] Figure 7 is the dynamic range of the device in Example 1 under positive bias (3V). DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation methods and drawings.

[0040] A tunneling photodiode with bias voltage to control dynamic range, the structural diagram of which is shown in FIG. Figure 1 As shown, it includes a conductive substrate, a first light absorption layer, a tunneling layer, a second light absorption layer and a metal electrode stacked in sequence from bottom to top; the first light absorption layer and the second light absorption layer form an I-type energy band heterojunction;

[0041] The metal electrode is a patterned electrode, and the metal electrode does not completely cover the second light absorbing layer;

[0042] The material of the first light absorption layer and the material of the second light absorption layer are any one of silicon, germanium, gallium arsenide, lead telluride, lead sulfide, lead selenide, indium gallium arsenide, indium phosphide, and mercury cadmium telluride, and the material of the first light absorption layer and the material of the second light absorption layer are different; the material of the tunneling layer is any one of aluminum oxide, zinc oxide, silicon oxide, silicon nitride, silver iodide, and indium gallium nitride; the metal electrode is made of any one of gold, nickel, chromium, titanium, and aluminum, or an alloy of at least two of them; the conductive substrate material is ITO, silver film, etc.

[0043] The thickness of the first light absorption layer is 0.2 μm to 500 μm, the thickness of the tunneling layer is 1 nm to 10 nm, the thickness of the second light absorption layer is 0.05 μm to 5 μm; and the thickness of the metal electrode is 10 nm to 100 nm.

[0044] Example 1

[0045] A method for preparing a tunneling photodiode with bias voltage-controlled dynamic range comprises the following steps:

[0046] Step 1: Select an N-type silicon wafer with a doping concentration of 1-20 Ω.cm as the first light-absorbing layer. The silicon wafer thickness is 500 μm. The substrate surface is cleaned to remove dirt and then baked at 200°C for 30 minutes to remove surface moisture. A conductive silver film is deposited on the bottom of the silicon by thermal evaporation to serve as the bottom electrode.

[0047] Step 2: A 3nm thick aluminum oxide film was deposited on top of the silicon wafer using atomic force deposition.

[0048] Step 3: A lead telluride thin film is prepared on the aluminum oxide film by magnetron sputtering. The film thickness is 150 nm and the film conductivity type is P-type.

[0049] Step 4: Use thermal evaporation to prepare a gold film on the lead telluride film. The gold film is in the shape of a square ring. The structural diagram is as shown below: Figure 2 As shown, the electrode thickness is 50 nm and the electrode line width is 0.2 μm, resulting in a tunneling photodiode.

[0050] Figure 3 The energy band diagram of the photodiode prepared in this embodiment of the present invention is shown in the figure. As can be seen from the figure, an I-type band heterojunction is formed between the N-type silicon and the P-type lead telluride thin film; at 0V, the diffusion and drift of charge carriers are balanced. The built-in electric field only allows thermal diffusion of majority carriers and drift of minority carriers, resulting in extremely low dark current (at the picoampere level, such as Figure 4 As shown). The introduction of the aluminum oxide layer further suppresses the thermal diffusion of majority carriers, effectively reducing the dark current, improving the device's weak light detection capability, and lowering the detection limit. Under reverse bias, the direction of the external electric field is the same as the built-in electric field, which enhances the depletion region, resulting in a lower dark current, which is mainly determined by the drift of minority carriers. As the electric field increases, the electrons undergo a DT process, causing the dark current to gradually increase and have different detection limits at different voltages. Under forward bias, the external electric field is opposite to the built-in electric field, weakening the depletion region, causing the dark current to be mainly determined by the diffusion of majority carriers. When the electric field exceeds the threshold voltage, electrons undergo field-induced tunneling (FNT), resulting in a significant increase in dark current and improving the detection limit in this mode.

[0051] The electrical characteristics of the tunneling photodiode prepared in this embodiment were tested using electrical software to test the response of the device under different light intensities. The light intensity range was 1E -5 mW / cm 2 -200mW / cm 2 .

[0052] Figure 4 This is a graph of the current-voltage characteristics of the device in Example 1 under zero bias in a dark environment. As can be seen from the graph, the tunneling diode has an extremely low dark current (as low as pA) under zero bias in a dark environment, greatly improving the device's low-light detection sensitivity.

[0053] Figure 5-Figure 7 The dynamic ranges of the photodiode prepared in this embodiment are respectively under zero bias, negative bias (-1V) and positive bias (3V). As can be seen from the figure, the tunneling diode can obtain different dynamic ranges by adjusting the bias voltage. The device corresponds to weak light (1E -5 mW / cm 2 -0.6mW / cm 2 ) response, medium intensity light (0.02mW / cm 2 -20mW / cm 2 ) response and strong light (4.5mW / cm 2 -200mW / cm 2 ) response, and the dynamic range under different bias voltages is both continuous and overlapping, ensuring that the dynamic range is seamless from low light to high light. The overall dynamic range of the device can cover 150dB.

[0054] The photodiode prepared in this embodiment can be applied to the fields of high dynamic range imaging and low-light detection. Specifically, high dynamic range imaging refers to the situation where, for example, when entering a dimly lit cave from a brightly lit cave, the human eye needs time to adapt to the change in light, and images taken by ordinary cameras are prone to overexposure outside the cave or underexposure inside the cave. HDR technology, by synthesizing images with different exposures, can simultaneously preserve the details of the sky and mountains outside the cave and the clarity of the rock walls and paths inside the cave, ensuring a natural transition between images. The photodiode prepared by the present invention through rapid electrical adjustment, with external biases of 0V, -1V, and 3V, can clearly image objects in low light, medium light, and high light, respectively. For low-light detection, such as in deep cave areas that rely entirely on artificial light sources, it is only necessary to adjust the working bias of the photodiode to the corresponding dynamic range (0V). At this time, clear imaging can be achieved without waiting for a long exposure delay.

[0055] Example 2

[0056] A method for preparing a tunneling photodiode with bias voltage-controlled dynamic range comprises the following steps:

[0057] Step 1: Indium phosphide is selected as the first light-absorbing layer with a thickness of 350 μm. The substrate surface is cleaned to remove dirt and baked at 200°C for 30 minutes to remove surface moisture. A conductive nickel film is deposited on the bottom of the indium phosphide by thermal evaporation to serve as the bottom electrode.

[0058] Step 2: Using metal organic chemical vapor deposition method to prepare zinc oxide film on the top of the indium phosphide substrate, the film thickness is 6nm;

[0059] Step 3: Using molecular beam epitaxy to grow an indium gallium arsenide thin film on the zinc oxide film, the film thickness is 100 nm;

[0060] Step 4: A gold film is prepared on the InGaAs film by thermal evaporation. The gold film is in a square ring shape, with an electrode thickness of 50 nm and an electrode line width of 0.2 μm, to obtain a tunneling photodiode.

[0061] Example 3

[0062] A method for preparing a tunneling photodiode with bias voltage-controlled dynamic range comprises the following steps:

[0063] Step 1: Select an N-type silicon wafer as the first light-absorbing layer. The thickness of the silicon wafer is 500 μm. Clean the surface of the substrate to remove dirt and bake it at 200°C for 30 minutes to remove surface moisture. Use thermal evaporation to deposit a conductive silver film on the bottom of the silicon to serve as the bottom electrode.

[0064] Step 2: A 5nm thick aluminum oxide film was deposited on top of the silicon wafer using atomic force deposition.

[0065] Step 3: Using molecular beam epitaxy to deposit a lead selenide thin film on the aluminum oxide film. The film thickness is 200 nm and the film conductivity type is P-type.

[0066] Step 4: A gold film is prepared on the lead selenide film by thermal evaporation. The gold film is in a square ring shape, with an electrode thickness of 50 nm and an electrode line width of 0.2 μm, to obtain a tunneling photodiode.

[0067] Comparative Example 1

[0068] A method for preparing a photodiode comprises the following steps:

[0069] Step 1: Select a germanium wafer with an N-type conductivity type as the first light-absorbing layer. The germanium wafer has a thickness of 500 μm. Clean the surface of the substrate to remove dirt and bake the substrate at 200°C for 30 minutes to remove surface moisture. Use thermal evaporation to prepare a conductive layer of silver film on the bottom of the germanium as the bottom electrode.

[0070] Step 2: A 5 nm thick aluminum oxide film was deposited on top of the germanium wafer using atomic force deposition.

[0071] Step 3: Using molecular beam epitaxy to deposit a lead telluride thin film on the aluminum oxide film. The film thickness is 200 nm and the film conductivity type is P-type.

[0072] Step 4: A gold film is prepared on the lead telluride film by thermal evaporation. The gold film is in a square ring shape, with an electrode thickness of 50 nm and an electrode line width of 0.2 μm, to obtain a photodiode.

[0073] In this comparative example, a heterojunction with type I energy band cannot be obtained.

[0074] Comparative Example 2

[0075] A method for preparing a photodiode comprises the following steps:

[0076] Step 1: Select a germanium wafer with an N-type conductivity type as the first light-absorbing layer. The germanium wafer has a thickness of 300 μm. Clean the surface of the substrate to remove dirt and bake the substrate at 200°C for 30 minutes to remove surface moisture. Use thermal evaporation to prepare a conductive silver film on the bottom of the germanium as the bottom electrode.

[0077] Step 2: Using molecular beam epitaxy to deposit a lead sulfide thin film on the zinc oxide film. The film thickness is 100 nm and the film conductivity type is P-type.

[0078] Step 3: A gold film is prepared on the lead sulfide film by thermal evaporation. The gold film is in a square ring shape, with an electrode thickness of 50 nm and an electrode line width of 0.2 μm, to obtain a photodiode.

[0079] This comparative example cannot obtain a tunneling photodiode with a continuously adjustable dynamic range.

[0080] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A tunneling photodiode with bias voltage-controlled dynamic range, characterized in that: The method comprises a conductive substrate, a first light absorption layer, a tunneling layer, a second light absorption layer and a metal electrode which are stacked in sequence from bottom to top; The first light absorbing layer and the second light absorbing layer form an I-type energy band heterojunction; The metal electrode is a patterned electrode, and the metal electrode does not completely cover the second light absorbing layer; Among them, the material of the first light absorption layer and the material of the second light absorption layer are any one of silicon, germanium, gallium arsenide, lead telluride, lead sulfide, lead selenide, indium gallium arsenide, indium phosphide, and mercury cadmium telluride, and the material of the first light absorption layer and the material of the second light absorption layer are different, and the band gap width is also different.

2. The tunneling photodiode with bias-controlled dynamic range according to claim 1, wherein: The material of the tunneling layer is any one of aluminum oxide, zinc oxide, silicon oxide, silicon nitride, silver iodide, and indium gallium nitride.

3. The tunneling photodiode with bias-controlled dynamic range according to claim 1, wherein: The metal electrode is made of any one of gold, nickel, chromium, titanium, and aluminum, or an alloy of at least two of them; the conductive substrate material is ITO, silver film, copper, gold, aluminum, nickel, or chromium.

4. The tunneling photodiode with bias-controlled dynamic range according to claim 1, wherein: The thickness of the first light absorption layer is 0.2 μm to 500 μm; the thickness of the tunneling layer is 1 nm to 10 nm; and the thickness of the second light absorption layer is 0.05 μm to 5 μm.

5. The tunneling photodiode with bias-controlled dynamic range according to claim 1, wherein: The thickness of the metal electrode is 10nm~100nm.

6. The method for controlling the dynamic range of a tunneling photodiode with bias voltage control according to any one of claims 1 to 5, wherein: The specific process is: Applying a positive bias voltage, which should be greater than the threshold voltage for tunneling, results in a high gain device suitable for strong light detection. When reverse bias is applied, the device gain is reduced, avoiding the saturation effect under strong light, which is suitable for medium-intensity light detection; When zero bias is applied, the device has extremely low dark current, and the optimized signal-to-noise ratio improves the sensitivity of weak light detection, making it suitable for weak light detection.

7. A method for preparing a tunneling photodiode with bias-controlled dynamic range according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: preparing a first light-absorbing layer on a conductive substrate, wherein the conductive substrate serves as a bottom electrode; Step 2: growing a tunneling layer on the first light absorbing layer; Step 3: growing a second light absorbing layer on the tunneling layer; Step 4: Deposit a metal electrode on the second light-absorbing layer as a top electrode.

8. The method for preparing a tunneling photodiode with bias-controlled dynamic range according to claim 7, wherein: The first light absorbing layer in step 1, the tunneling layer in step 2, and the second light absorbing layer in step 3 are formed by any one of molecular beam epitaxy, atomic force deposition, metal organic chemical vapor deposition, magnetron sputtering, or thermal evaporation.

9. Application of the tunneling photodiode with bias-controlled dynamic range according to any one of claims 1 to 5 in the fields of high dynamic range imaging and weak light detection, characterized in that: The high dynamic range imaging is to apply 0V, -1V and 3V bias to the tunneling photodiode to achieve clear imaging of weak light objects, medium-light objects and strong light objects respectively; the application in the field of low-light detection is specifically to apply 0V bias to the tunneling photodiode to achieve clear imaging.

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