Inter-band cascade infrared photon detector and preparation method thereof

Abstract

The invention discloses an inter-band cascade infrared photon detector, the light incidence mode of the detector is normal incidence, the table top of the detector is a circular table top, the detector comprises a substrate, an N-type contact layer, a plurality of cascade regions and a P-type contact layer from bottom to top, and N is a positive integer; the cascade region comprises an electron barrier layer, an absorption layer and a hole barrier layer from bottom to top, the electron barrier layer is of a multi-quantum well structure, the absorption layer is a superlattice, and the hole barrier layer is of a gradient multi-quantum well structure. The device has the characteristics of good bandwidth performance and high quantum efficiency.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detectors, and in particular to an inter-band cascade infrared photon detector and a preparation method thereof. Background Art

[0002] 3-5μm mid-wave infrared (MWIR) is an important atmospheric window, and the atmospheric environment is transparent to the absorption of this window band. The rational use of these bands, the development of photoelectric detectors, and the military deployment of the three-in-one strategy for land, sea and air are of great strategic significance. In the military, it can be used for aerospace remote sensing, infrared military detection, and infrared guidance. In environmental detection, infrared detectors can be used for global ice cloud detection and analysis of climate change. Deep space extraterrestrial exploration, medical imaging, combined with artificial intelligence, build digital cities and smart earth. In addition, in the application of communications, the deployment of ground-to-air high-speed communication systems is crucial to the development of global broadband networks. Mid-infrared wavelengths provide many advantages for building such systems and are widely used in building free-space optical communication systems with low atmospheric attenuation and resistance to severe weather conditions. Photoelectric detectors, as a key component of light detection and ranging systems, have very important applications in the fields of automotive autonomous driving sensing and gas monitoring.

[0003] With the rapid development of mid-infrared devices, high-performance infrared light sources such as quantum cascade lasers, interband cascade lasers, etc. have been explored. Mid-infrared optical frequency combs with wide spectral range, high resolution, and fast acquisition time have been explored. However, the development of high-speed photodetectors lags behind other mid-infrared devices and has become a shortcoming that restricts the system. It is urgent to develop a detector with high bandwidth and high quantum efficiency.

[0004] The relatively short diffusion length and short carrier lifetime at high temperatures have led to the degradation of the performance of traditional detectors at high temperatures. Since the ICIP (interband cascade infrared photodetector) was proposed in 2005, its discrete absorption layer structure can circumvent these problems and has the ability to operate at high temperatures and high speeds. ICIP is composed of multiple cycles in series, and the thickness of a single-stage absorption layer can be less than the diffusion length to reduce the recombination of photogenerated carriers during the diffusion process, while the total absorption layer thickness can be greater than the diffusion length to ensure sufficient light absorption. Such a structure has also been verified to have the advantages of low noise, high temperature operation, and high-speed response.

[0005] However, the current research on inter-band cascade detectors is mainly focused on the theoretical and imaging levels, and the potential of the device in terms of frequency response has not been fully developed. The 3dB bandwidth of the ICIP reported so far is roughly within 10G, which is affected by the higher device RC time constant, significant current mismatch, and longer absorption layer design. The present invention optimizes the structural design of the ICIP, and through simulation analysis, selects the appropriate absorption layer thickness and the number of cascade regions, which helps to maintain a high quantum efficiency while improving the bandwidth performance of the device.

[0006] The Chinese invention application with application number 202011463550.9 discloses "An inter-band cascade detector and its manufacturing method", and its technical solution is: the inter-band cascade detector is composed of multiple cascade steps, and each cascade step includes an electron barrier layer, a superlattice absorption layer and a hole barrier layer. The first to third superlattice absorption layers adopt InAs / InAsSb type II superlattice. The technical problem solved by its technical solution is how to reduce the dark current level and improve the detection rate of the inter-band cascade detector. Therefore, its technical solution is different from the technical problem to be solved by the present invention, and its adopted technical solution cannot solve the technical problem proposed by the present invention. Summary of the invention

[0007] In order to solve the technical problems of the existing cascade detectors, such as the carrier transport is not smooth enough, the carrier collection speed is slow, and the transit time limit bandwidth is small, the present invention proposes an inter-band cascade infrared photon detector and a preparation method thereof. The technical solution adopted by the present invention is:

[0008] The first aspect of the present invention provides an inter-band cascade infrared photon detector, wherein the detector has normal incidence as the light input mode, and the detector table is a circular table, which includes, from bottom to top, a substrate, an N-type contact layer, a plurality of cascade regions and a P-type contact layer; the cascade region includes, from bottom to top, an electron barrier layer, an absorption layer and a hole barrier layer, wherein the electron barrier layer is a multi-quantum well structure, the absorption layer is a superlattice, and the hole barrier layer is a gradient multi-quantum well structure.

[0009] As a preferred solution, the diameter of the detector table is 20 μm.

[0010] As a preferred solution, the material of the N-type contact layer is N-type heavily doped GaSb material.

[0011] As a preferred solution, the electron barrier layer adopts an AlSb / GaSb / AlSb / GaSb / AlSb multiple quantum well structure, the thickness of AlSb is set to 1.6nm, the thickness of GaSb is set to 3.0nm, the valence band energy level position is 0.501eV, which is aligned with the lowest conduction band energy level of 0.502eV in the relaxation zone, and is higher than the valence band of the absorption layer.

[0012] As a preferred solution, the absorption layer adopts lightly P-type doped 8ML-InAs / 8ML-GaSb superlattice material, the thickness of the absorption layer is designed to be 300nm, the band gap size of the InAs / GaSb superlattice is 0.256eV, the position of the conduction band microband is 0.698eV, and the position of the valence band microband is 0.442eV.

[0013] As a preferred solution, the hole barrier layer adopts a gradient InAs / AlSb multiple quantum well structure, the thickness of AlSb is set to 2.5nm, the thickness of InAs is set to 3.7nm to 8.0nm, the conduction band energy level corresponding to the hole barrier layer is 0.698eV to 0.502eV, and the conduction band of the hole barrier layer is aligned with the conduction band of the absorption layer.

[0014] As a preferred solution, the P-type contact layer is made of P-type heavily doped GaSb material.

[0015] As a preferred solution, the number N of the cascade zones is set to 3.

[0016] As a preferred solution, the substrate is made of GaSb material.

[0017] A second aspect of the present invention provides a method for preparing an inter-band cascade infrared photon detector, the method comprising the following steps:

[0018] S1: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the P electrode, and develop to expose the evaporation area, and then evaporate the P metal. After the evaporation is completed, soak in acetone to oxygenate and remove the photoresist;

[0019] S2: Spin-coating HSQ on the epitaxial wafer and performing electron beam exposure to define the location of the P table;

[0020] S3: dry etching is performed using an inductively coupled plasma etching system, passing through the entire cascade region to reach the N contact layer, and the sidewalls of the P pillars are acid-treated using a solution of HCl:H2O=1:5;

[0021] S4: using a reactive ion beam etching system to etch the HSQ glue on the P table to expose the P table;

[0022] S5: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the N mesa position, and then develop, leaving the photoresist on the N mesa position as a mask for wet etching;

[0023] S6: Use citric acid solution to wet-etch the device to etch out the N-table, and then soak in acetone to remove the glue;

[0024] S7: performing a planarization operation, baking and forming, and forming a sidewall passivation, wherein the planarization operation is performed by using a chemical vapor deposition system or spin coating BCB glue;

[0025] S8: Spin-coat negative resist AZ2035 on the epitaxial wafer, expose with maskless UV light machine, use reactive ion beam etching system to etch open N window and form coplanar waveguide structure, and remove resist with acetone;

[0026] S9: Spin-coat negative photoresist AZ2035, use a maskless exposure machine to expose the evaporation area, perform metal evaporation, and serve as a seed layer for subsequent electroplating;

[0027] S10: prepare the air bridge structure by wafer electroplating, and remove the glue by acetone ultrasonic method. The whole process is now completed.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention improves the bandwidth performance of ICIP while ensuring high absorption efficiency through smooth optimization of the energy band structure and design selection of the absorption layer thickness and the number of cascade cycles. The present invention ensures the average quantum efficiency of each level by selecting a design level of 3 and a thickness of the absorption region of each level of 300nm. At the same time, the influence of the current mismatch on the low level is reduced, which is beneficial to improving the bandwidth performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 An epitaxial structure diagram of an inter-band cascade infrared photon detector provided in this embodiment;

[0031] Figure 2 The energy band structure diagram of a single cascade region of ICIP provided in this embodiment;

[0032] Figure 3 The simulation diagram of average quantum efficiency calculation of each level for level 3, level 4, and level 5 ICIP provided in this embodiment at different absorption layer thicknesses;

[0033] Figure 4 The bandwidth simulation diagram of the 300nm absorption layer thickness under the drift model provided in this embodiment;

[0034] Figure 5 This is a schematic diagram of the three-dimensional structure of the device provided in this embodiment.

[0035] Figure 6 The device preparation flow chart provided in this embodiment. DETAILED DESCRIPTION

[0036] The accompanying drawings are only used for illustrative purposes and are not to be construed as limiting the present invention;

[0037] It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the embodiments of the present application.

[0038] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0039] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0040] In addition, in the description of this application, unless otherwise specified, "multiple" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0041] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0042] Example 1

[0043] Please refer to Figure 1 as well as Figure 2This embodiment provides an inter-band cascade infrared photon detector, wherein the detector has normal incidence as the light input mode, and the detector table is a circular table, which includes, from bottom to top, a substrate, an N-type contact layer, a plurality of cascade regions and a P-type contact layer, wherein N is a positive integer; the cascade region includes, from bottom to top, an electron barrier layer, an absorption layer and a hole barrier layer, wherein the electron barrier layer is a multi-quantum well structure, the absorption layer is a superlattice, and the hole barrier layer is a gradient multi-quantum well structure.

[0044] Example 2

[0045] This embodiment can be regarded as an improved or extended embodiment of Embodiment 1, specifically:

[0046] Please refer to Figure 1 as well as Figure 2 , an inter-band cascade infrared photon detector, the detector has normal incidence as the light input mode, the detector table is a circular table, and comprises from bottom to top a substrate, an N-type contact layer, a plurality of cascade regions and a P-type contact layer, wherein N is a positive integer; the cascade region comprises from bottom to top an electron barrier layer, an absorption layer and a hole barrier layer, wherein the electron barrier layer is a multi-quantum well structure, the absorption layer is a superlattice, and the hole barrier layer is a gradient multi-quantum well structure.

[0047] In a specific embodiment, the diameter of the detector table is 20 μm.

[0048] In a specific embodiment, the material of the N-type contact layer is N-type heavily doped GaSb material to form a good ohmic contact and also serves as a buffer layer between the N-type contact layer and the GaSb substrate.

[0049] In a specific embodiment, the electron barrier layer adopts an AlSb / GaSb / AlSb / GaSb / AlSb multiple quantum well structure, the thickness of AlSb is set to 1.6nm, the thickness of GaSb is set to 3.0nm, the valence band energy level position is 0.501eV, which is aligned with the lowest conduction band energy level of 0.502eV in the relaxation zone, and is higher than the valence band of the absorption layer.

[0050] In a specific embodiment, the absorption layer adopts lightly P-type doped 8ML-InAs / 8ML-GaSb superlattice material, the absorption layer thickness is designed to be 300nm, the InAs / GaSb superlattice band gap size is 0.256eV, the conduction band microband position is 0.698eV, and the valence band microband position is 0.442eV.

[0051] In a specific embodiment, the hole barrier layer adopts a gradient InAs / AlSb multiple quantum well structure, the thickness of AlSb is set to 2.5nm, the thickness of InAs is set to 3.7nm to 8.0nm, the conduction band energy level position corresponding to the hole barrier layer is 0.698eV to 0.502eV, and the conduction band of the hole barrier layer is aligned with the conduction band of the absorption layer.

[0052] In a specific embodiment, the P-type contact layer is made of P-type heavily doped GaSb material.

[0053] In a specific embodiment, the number N of the cascade zones is set to 3.

[0054] In a specific embodiment, the substrate is made of GaSb material.

[0055] The present invention designs the thickness of the absorption layer to be 300 nm, which can significantly improve the bandwidth of the device while maintaining a relatively high quantum efficiency.

[0056] After calculation and analysis, when the number of cascade regions N is set to 3, the maximum quantum efficiency can be achieved when the thickness of the three-level ICIP is 500nm. At this time, the average quantum efficiency of each level is 8.56%. However, the quantum efficiency tends to saturate before the thickness is close to 500nm. Increasing the thickness of the absorption layer has little effect on the improvement of efficiency, but it increases the current mismatch factor (describing the current mismatch of each level) by several times. At the same time, the carrier transit time (the time required for the carrier to be generated from the absorption zone to be collected) increases, affecting the 3dB bandwidth performance of the device. The absorption layer thickness is designed to be 300nm, and the current mismatch factor is only 14.7% of that at 500nm. The 300nm absorption layer thickness device calculated by the drift model will be 4.93GHz higher than the 500nm absorption layer device.

[0057] When the number N of the cascade regions is set to 3, the total absorption layer thickness of the three-level structure reaches 900nm, which can ensure good average quantum efficiency at each level. At the same time, the three-level structure device is less affected by current mismatch, which is beneficial to improving the bandwidth performance of the device.

[0058] Compared with level 4 and level 5 ICIP, the average quantum efficiency of each level of level 3 ICIP is slightly higher. Under the same 300nm absorption layer thickness, the average quantum efficiency of each level of level 3 ICIP is 7.71%, while that of level 4 and level 5 ICIP is 7.29% and 6.90% respectively. In addition, the current mismatch factor C of level 3 ICIP is small. After calculation and analysis, the current mismatch factor of level 3 ICIP is only 56.5% of that of level 4 and 37.4% of that of level 5. Level 3 devices are less affected by current mismatch, and the device bandwidth is negatively correlated with the current mismatch factor. The bandwidth performance of level 3 devices is better. In the fitting of the drift model, the device bandwidth is related to the electric field strength. The thickness of the single-level absorption layer is set to 300nm, and the total thickness of the 3-level ICIP absorption layer is about 900nm. The bandwidth value can be close to that of the 300nm single absorption layer device, and the bandwidth average is 0.70GHz smaller. The 4th and 5th level ICIPs are affected by the current mismatch, and the bandwidth averages decrease by 1.26G and 1.92G respectively, indicating that the bandwidth performance of the 3-level ICIP is better.

[0059] Figure 3 The calculation and analysis of the average quantum efficiency of each level of 3, 4, and 5 ICIPs with different absorption layer thicknesses show that the average quantum efficiency of each level is relatively close. Compared with the 4 and 5 ICIPs, the average quantum efficiency of each level of 3 ICIP is relatively high. For the 3-level ICIP, when the thickness of each level of absorption layer is 300nm, the average quantum efficiency is 7.71%, slightly lower than the 8.56% of 500nm. However, in terms of bandwidth performance, the thickness of each level of absorption layer is 300nm, which is 4.93GHz higher than the 500nm thickness device.

[0060] Figure 4 For bandwidth simulation under the drift model, the thickness of the single-stage absorption layer is 300nm. Affected by the current mismatch, the average bandwidth of the 3-level, 4-level, and 5-level ICIPs under each electric field decreased by 0.70GHz, 1.26GHz, and 1.92GHz respectively compared with the 300nm thick device, indicating that the 3-level ICIP is less affected by the current mismatch and the device has a higher 3dB bandwidth.

[0061] Figure 5 Schematic diagram of the device structure. The parasitic capacitance of the device is reduced by using double steps, air bridges and other structures, and the intrinsic capacitance of the device is reduced by reducing the table size, so as to improve the RC time limit bandwidth of the device.

[0062] Example 3

[0063] Please refer to Figure 5 as well as Figure 6 This embodiment provides a method for preparing an inter-band cascade infrared photon detector, the method comprising the following steps:

[0064] S1: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the P electrode, and develop to expose the evaporation area, and then evaporate the P metal. After the evaporation is completed, soak in acetone to oxygenate and remove the photoresist;

[0065] S2: Spin-coating HSQ on the epitaxial wafer and performing electron beam exposure to define the location of the P table;

[0066] S3: dry etching is performed using an inductively coupled plasma etching system, passing through the entire cascade region to reach the N contact layer, and the sidewalls of the P pillars are acid-treated using a solution of HCl:H2O=1:5;

[0067] S4: using a reactive ion beam etching system to etch the HSQ glue on the P table to expose the P table;

[0068] S5: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the N mesa position, and then develop, leaving the photoresist on the N mesa position as a mask for wet etching;

[0069] S6: Use citric acid solution to wet-etch the device to etch out the N-table, and then soak in acetone to remove the glue;

[0070] S7: performing a planarization operation, baking and forming, and forming a sidewall passivation, wherein the planarization operation is performed by using a chemical vapor deposition system or spin coating BCB glue;

[0071] S8: Spin-coat negative resist AZ2035 on the epitaxial wafer, expose with maskless UV light machine, use reactive ion beam etching system to etch open N window and form coplanar waveguide structure, and remove resist with acetone;

[0072] S9: Spin-coat negative photoresist AZ2035, use a maskless exposure machine to expose the evaporation area, perform metal evaporation, and serve as a seed layer for subsequent electroplating;

[0073] S10: prepare the air bridge structure by wafer electroplating, and remove the glue by acetone ultrasonic method. The whole process is now completed.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An inter-band cascade infrared photon detector, wherein the detector has normal incidence as the light input mode and the detector table is a circular table, characterized in that: From bottom to top, it includes a substrate, an N-type contact layer, a plurality of cascade regions and a P-type contact layer; the cascade region includes from bottom to top an electron barrier layer, an absorption layer and a hole barrier layer, wherein the electron barrier layer is a multi-quantum well structure, the absorption layer is a superlattice, and the hole barrier layer is a gradient multi-quantum well structure.

2. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The diameter of the detector table is 20 μm.

3. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The material of the N-type contact layer is N-type heavily doped GaSb material.

4. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The electron barrier layer adopts an AlSb / GaSb / AlSb / GaSb / AlSb multiple quantum well structure, the thickness of AlSb is set to 1.6nm, the thickness of GaSb is set to 3.0nm, the valence band energy level position is 0.501eV, which is aligned with the lowest conduction band energy level 0.502eV in the relaxation zone and is higher than the valence band of the absorption layer.

5. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The absorption layer adopts lightly P-type doped 8ML-InAs / 8ML-GaSb superlattice material, the thickness of the absorption layer is designed to be 300nm, the band gap size of the InAs / GaSb superlattice is 0.256eV, the position of the conduction band microband is 0.698eV, and the position of the valence band microband is 0.442eV.

6. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The hole barrier layer adopts a gradient InAs / AlSb multi-quantum well structure, the thickness of AlSb is set to 2.5nm, the thickness of InAs is set to 3.7nm to 8.0nm, the conduction band energy level corresponding to the hole barrier layer is 0.698eV to 0.502eV, and the conduction band of the hole barrier layer is aligned with the conduction band of the absorption layer.

7. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The P-type contact layer is made of P-type heavily doped GaSb material.

8. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The number N of the cascade zones is set to 3.

9. The inter-band cascade infrared photon detector according to claim 1, characterized in that: The substrate is made of GaSb material.

10. A method for preparing an inter-band cascade infrared photon detector, characterized in that: The method comprises the following steps: S1: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the P electrode, and develop to expose the evaporation area, and then evaporate the P metal. After the evaporation is completed, soak in acetone to oxygenate and remove the photoresist; S2: Spin-coating HSQ on the epitaxial wafer and performing electron beam exposure to define the location of the P table; S3: dry etching is performed using an inductively coupled plasma etching system, passing through the entire cascade region to reach the N contact layer, and the sidewalls of the P pillars are acid-treated using a solution of HCl:H2O=1:5; S4: using a reactive ion beam etching system to etch the HSQ glue on the P table to expose the P table; S5: Spin-coat the negative photoresist AZ2035 on the epitaxial wafer, use a maskless exposure machine to expose the N mesa position, and then develop, leaving the photoresist on the N mesa position as a mask for wet etching; S6: Use citric acid solution to wet-etch the device to etch out the N-table, and then soak in acetone to remove the glue; S7: performing a planarization operation, baking and forming, and forming a sidewall passivation, wherein the planarization operation is performed by using a chemical vapor deposition system or spin coating BCB glue; S8: Spin-coat negative resist AZ2035 on the epitaxial wafer, expose with maskless UV light machine, use reactive ion beam etching system to etch open N window and form coplanar waveguide structure, and remove resist with acetone; S9: Spin-coat negative photoresist AZ2035, use a maskless exposure machine to expose the evaporation area, perform metal evaporation, and serve as a seed layer for subsequent electroplating; S10: prepare the air bridge structure by wafer electroplating, and remove the glue by acetone ultrasonic method. The whole process is now completed.

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