A high temperature infrared detector with improved potential barrier and manufacturing method thereof

Abstract

The present invention provides a high-temperature infrared detector with an improved barrier, comprising: a buffer layer, a first N-type ohmic contact layer, an N-type long-wave absorption layer, an improved superlattice barrier layer, and a second N-type ohmic contact layer epitaxially grown in sequence on a substrate; the improved superlattice barrier layer covers the space charge region of the heterojunction formed by the N-type long-wave absorption layer and the second N-type ohmic contact layer. The structure disclosed in the present invention realizes an infrared detector that can maintain a low dark current level at high temperature through the design of the device structure, and the structure is simple; through the design and optimization of the improved superlattice barrier layer, the generation of composite dark current and tunneling dark current in the device is greatly suppressed, while the quantum efficiency of the detector is improved. The present invention also provides a method for manufacturing a high-temperature infrared detector with an improved barrier.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor optoelectronic devices, and in particular relates to a high-temperature infrared detector with an improved potential barrier. Background Art

[0002] The core competitiveness of the new generation of infrared focal plane detectors will focus on "SWaP 3 ", that is, smaller size (Size), smaller weight (Weight), lower power consumption (Power consumption), higher performance (performance) and lower cost (Price). Among them, increasing the operating temperature of infrared detectors becomes the key. The volume, weight and power consumption of current photovoltaic high-performance infrared detectors mainly come from mechanical refrigerators. Realizing high operating temperature (High Operation Temperature, HOT) infrared detectors can greatly reduce the size of refrigerators, reduce the weight and power consumption of the entire machine, and thus reduce the cost of infrared detection systems and improve system stability. However, as the operating temperature of infrared detectors increases, the diffusion current and generation-recombination current index caused by thermally excited carriers increase. Therefore, how to maintain high detection performance while increasing the operating temperature of infrared detectors has become a SWaP 3 Core scientific and technological issues in development.

[0003] Infrared detection technology has important and extensive applications in the fields of space-to-earth detection, manned spaceflight, target search and tracking, medical and industrial thermal imaging, etc. Among them, long-wave infrared detection technology has irreplaceable application value for atmospheric temperature and humidity element distribution monitoring and astronomical observation. The rapid development of molecular beam epitaxy technology has made antimonide type II superlattice an ideal infrared photoelectric detection material, with significant advantages such as low Auger recombination rate, high effective carrier mass, good material uniformity, and relatively cheap focal plane cost. Among them, InAs / InAsSb type II superlattice has been proven to have a longer carrier lifetime than InAs / GaSb type II superlattice in recent years, and has shown outstanding advantages in the development of high-temperature and high-performance long-wave infrared focal plane detectors. The current type II superlattice high-temperature infrared detector is mainly an nBn structure, that is, the absorption region is N-type doped or unintentionally doped, the ohmic contact layer is N-type doped, and the barrier layer is unintentionally doped. The InAs / InAsSb type II superlattice has the characteristics of intrinsic N-type doping, which is very suitable as the material for the absorption region in the nBn structure high-temperature infrared detector. Currently, the common InAs / InAsSb II superlattice nBn high-temperature infrared detector mainly uses AlSb as the material for the barrier layer. However, the valence band of AlSb is slightly higher than the valence band of the InAs / InAsSb II superlattice, which will not only cause the band bending at the interface between the absorption region and the barrier layer, but also form a hole potential well between the absorption region and the ohmic contact layer, which will affect the two major performance indicators of the detector, namely the quantum efficiency and dark current level. To this end, the present invention designs a high-temperature infrared detector with an improved barrier and a method for manufacturing the same. By changing the material and structure of the barrier layer in the nBn high-temperature infrared detector, the valence band of the barrier layer and the valence band of the absorption region are aligned, thereby further improving the detection performance of the high-temperature infrared detector. Summary of the invention

[0004] The purpose of the present invention is to design a high temperature infrared detector with an improved potential barrier to solve the following existing technical problems:

[0005] 1. The current mainstream InAs / InAsSb II superlattice nBn high-temperature infrared detector uses AlSb as the barrier layer, which causes band bending at the interface between the absorption region and the barrier layer, resulting in an increase in the generation-composite dark current in the absorption region;

[0006] 2. The current mainstream InAs / InAsSb type II superlattice nBn high-temperature infrared detector uses AlSb as the barrier layer, which creates a hole barrier between the absorption region and the ohmic contact layer, reducing the quantum efficiency of the device.

[0007] The present invention adopts the following technical solution:

[0008] One aspect of the present invention provides a high-temperature infrared detector with an improved potential barrier, comprising: an N-type long-wave absorption layer, an improved superlattice barrier layer epitaxially formed on the N-type long-wave absorption layer, and an N-type ohmic contact layer epitaxially formed on the improved superlattice barrier layer; the improved superlattice barrier layer covers the space charge region formed between the N-type long-wave absorption layer and the N-type ohmic contact layer.

[0009] Furthermore, the high-temperature infrared detector with improved potential barrier also includes: a substrate, a buffer layer, a first electrode and a second electrode; the buffer layer is epitaxially grown on the substrate, and the N-type long-wave absorption layer is epitaxially grown on the buffer layer.

[0010] Furthermore, the substrate is composed of undoped GaSb.

[0011] Furthermore, the buffer layer has a thickness of 500-1000 nm and is composed of Si-doped InAsSb, and the Si doping concentration is 1×10 17 cm -3 ~1×10 18 cm -3 .

[0012] Furthermore, the N-type long-wave absorption layer has a thickness of 3-6 μm and is composed of a Si-doped InAs / InAsSb superlattice, each period of which is composed of 25-30 ML InAs and 5-7 ML InAsSb, and the Si doping concentration is 1×10 16 cm -3 ~1×10 17 cm -3 .

[0013] Furthermore, the improved superlattice barrier layer has a thickness of 400nm-500nm and is composed of undoped InAs / AlAs / InAs / InAsSb superlattice, with each period consisting of 12-16ML InAs, 1-2ML AlAs, and 5-7ML InAsSb, wherein the InAsSb layer thickness in each period is the same as the InAsSb layer thickness in each period of the N-type long-wave absorption layer.

[0014] Furthermore, the N-type ohmic contact layer has a thickness of 200-400 nm and is composed of a Si-doped InAs / InAsSb superlattice, each period of which is composed of 25-30 ML InAs and 5-7 ML InAsSb, and the Si doping concentration is 1×10 17 cm -3 ~1×10 18 cm -3 .

[0015] At the same time, another aspect of the present invention provides a method for manufacturing an NBP type barrier superlattice high-temperature infrared detector, the steps comprising: S1: forming a buffer layer, an N-type long-wave absorption layer, an improved superlattice barrier layer, and an N-type ohmic contact layer stacked in sequence by epitaxial growth on the substrate; S2: forming a table consisting of the N-type long-wave absorption layer, the improved superlattice barrier layer, and the N-type ohmic contact layer on the buffer layer; S3: establishing a first electrode and a second electrode on the surface of the buffer layer and the surface of the N-type ohmic contact layer, respectively.

[0016] Furthermore, the growth method of the stacked structure is molecular beam epitaxy.

[0017] Furthermore, the method for forming the mesa on the buffer layer is photolithography etching, comprising:

[0018] Spin coating a photoresist on the surface of the stacked structure;

[0019] Using mask photolithography and development methods to form a photoresist covering pattern on the surface of the N-type ohmic contact layer;

[0020] The wet chemical etching method is used to etch the portion of the N-type ohmic contact layer surface not covered by the photoresist pattern to the buffer layer, thereby forming a mesa consisting of the N-type long-wave absorption layer, the improved superlattice barrier layer, and the N-type ohmic contact layer.

[0021] Furthermore, a first electrode is grown on the surface of the buffer layer by electron beam evaporation coating; and a second electrode is grown on the table surface of the N-type ohmic contact layer by electron beam evaporation coating.

[0022] The beneficial effects brought by the present invention are:

[0023] 1. Through the design of the barrier structure and doping control, the overall spatial electric field of the device is confined to the wide bandgap barrier region, thereby greatly reducing the generation-recombination dark current and tunneling dark current in the absorption region; at the same time, according to the rapid decrease of the generation-recombination current as the band gap widens, and the dark current fitting results show that the generation-recombination current in the barrier region does not contribute much to the overall dark current level of the device.

[0024] 2. Due to the reasonable and precise regulation of the periodic thickness and total thickness of the barrier layer superlattice of the present invention, the theoretical calculation results show that the valence band at each heterojunction interface is smooth and unobstructed without spikes and barriers, and has good carrier transport performance. In this case, the photogenerated minority carriers, i.e., holes, can be smoothly moved to the electrode through drift action, thereby improving the quantum efficiency; BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a high-temperature infrared detector with an improved potential barrier of the present invention;

[0026] Figure 2 It is a schematic diagram of the theoretical device energy band of a high-temperature infrared detector with improved potential barrier under a bias voltage of 0.1V;

[0027] Figure 3 It is the current-voltage characteristic curve of a high-temperature infrared detector with improved potential barrier at different temperatures of the present invention;

[0028] Figure 4 The present invention is a flow chart of a method for manufacturing a high-temperature infrared detector with an improved potential barrier. DETAILED DESCRIPTION

[0029] According to the energy band structure characteristics of the superlattice infrared detector, the present invention designs and manufactures a simple-structured superlattice high-temperature infrared detector through energy band engineering. The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments, but it is not intended to limit the patent of the present invention.

[0030] A high temperature infrared detector with improved potential barrier, such as Figure 1 As shown, it specifically includes: a substrate 1, a buffer layer 2, an N-type long-wave absorption layer 3, an improved superlattice barrier layer 4, an N-type ohmic contact layer 5, a first electrode 6 and a second electrode 7.

[0031] Substrate 1, prepared by material including unintentionally doped GaSb.

[0032] The buffer layer 2 is epitaxially grown on the substrate 1, and the preparation material includes Si-doped InAsSb. Preferably, the thickness of the buffer layer 2 is 500nm, the composition of Sb is 0.09, and the doping concentration of Si is specifically selected to be 1×10 18 cm -3 .

[0033] The N-type long-wave absorption layer 3 is epitaxially grown on the buffer layer 2, with a thickness of 3-6 μm. The preparation material includes: Si-doped InAs / InAsSb superlattice, each period is composed of 25-30 ML InAs and 5-7 ML InAsSb, and the Si doping concentration is 1×10 16 cm -3 ~1×10 17 cm -3 Preferably, the InAs / InAsSb period thickness is 28ML / 7ML, the Sb composition in InAsSb is 0.5, and the doping concentration of Si is specifically selected to be 1×10 16 cm -3 The bandgap width of the N-type long-wave absorption layer 3 designed in this way is 108.1 meV at 150K, and the absorption wavelength is 11.5 μm. Preferably, the thickness of the N-type long-wave absorption layer 3 is specifically selected to be 4 μm.

[0034] The improved superlattice barrier layer 4 is epitaxially grown on the N-type long-wave absorption layer 3, with a thickness of 400nm-500nm. The preparation materials include: non-intentionally doped InAs / AlAs / InAs / InAsSb superlattice, each period is composed of 12-16ML InAs, 1-2MLAlAs, 5-7ML InAsSb, wherein the thickness of the InAsSb period in each period is the same as the thickness of the InAsSb period in the N-type long-wave absorption layer. Preferably, the thickness of the InAs / AlAs / InAs / InAsSb period is 6.5ML / 1.5ML / 6.5ML / 7ML. The bandgap width of the improved superlattice barrier layer 4 designed in this way is 195.6meV at 150K. Preferably, the thickness of the improved superlattice barrier layer 4 is 480nm.

[0035] The N-type ohmic contact layer 5 has a thickness of 200-400 nm and is epitaxially grown on the improved superlattice barrier layer 4. The preparation material includes: Si-doped InAs / InAsSb superlattice, each period of which is composed of 25-30ML InAs and 5-7ML InAsSb, and the Si doping concentration is 1×10 17 cm -3 ~1×10 18 cm -3 Preferably, the InAs / InAsSb period thickness is 28ML / 7ML, the Sb composition in InAsSb is 0.5, and the doping concentration of Si is specifically selected to be 5×10 17 cm -3 The band gap width of the N-type ohmic contact layer 5 designed in this way is 108.1 meV at 150 K. Preferably, the thickness of the N-type ohmic contact layer 5 is specifically selected to be 400 nm.

[0036] After the material growth is completed, a photoresist-covered pattern is formed on the N-type ohmic contact layer 5 by mask photolithography and development methods, and then a wet chemical etching method is used to etch the portion of the surface of the N-type ohmic contact layer 5 that is not covered by the photoresist pattern to the buffer layer 2, thereby forming a mesa composed of the N-type long-wave absorption layer, the improved superlattice barrier layer, and the N-type ohmic contact layer on the buffer layer. Preferably, the etching solution is a citric acid:phosphoric acid solution, the etching rate is about 500nm / min, and the etching time is about 10min.

[0037] After the terrace is formed, the first electrode 6 is grown on the surface of the buffer layer 2 by electron beam evaporation. The second electrode 7 is grown on the N-type ohmic contact layer 5 by electron beam evaporation.

[0038] In specific operation, the present invention can adjust the periodic thickness of the InAs layer, InAsSb layer, and AlAs layer in each layer of the superlattice structure and the total thickness of the superlattice so that the overall valence band of the device is smooth and the valence band discontinuity between different layers is close to zero.

[0039] Limiting the doping concentration of Si in the N-type long-wave absorption layer 3 and the N-type ohmic contact layer 5 within the above range is beneficial to reducing the density of defects and generation-recombination centers in the device, and is beneficial to reducing dark current.

[0040] The present invention forms an nBn single barrier heterojunction structure by growing a modified superlattice barrier layer 4 between an N-type long-wave absorption layer 3 and an N-type ohmic contact layer 5, and maintains a nearly zero valence band discontinuity between the N-type long-wave absorption layer 3, the modified superlattice barrier layer 4 and the N-type ohmic contact layer 5 by adjusting the thickness of each layer of superlattice, the superlattice composition and the doping concentration, so that holes in the device can be transported without hindrance, thereby ensuring good response performance.

[0041] When the layer structure provided by the present invention is irradiated with 8-11.5μm long-wave infrared light, photogenerated electron-hole pairs are first generated in the N-type long-wave absorption layer 3, wherein the majority electrons move toward the improved superlattice barrier layer 4 under the action of diffusion, but cannot pass through the improved superlattice barrier layer 4 of the high valence band; the minority holes drift toward the improved superlattice barrier layer 4 under the action of the electric field, and since the designed device valence band is smooth and unobstructed at the interface of each layer, the holes can be transported unimpeded to the N-type ohmic contact layer 5 and finally collected by the electrode, converting the optical signal into an electrical signal for output.

[0042] The structural design of the present invention makes the IV characteristic curve of the device at different temperatures as follows: Figure 3 As shown by Figure 3 It can be seen that the device is under a reverse bias voltage of less than 0.5V, and the dark current density does not exceed 1×10 at 77K. -7 Acm -3 , the dark current density is about 3×10 -4 Acm -3 Therefore, the present invention is an infrared detector structure that still maintains high performance at high temperatures.

[0043] In summary, the present invention utilizes the characteristic of the superlattice structure that it is easy to control the energy band, introduces a single barrier structure, and greatly suppresses the GR current and tunneling current in the space charge region through the wide bandgap of the barrier. By precisely and reasonably controlling the superlattice thickness and doping control, the quantum efficiency and responsiveness of the device are improved and the overall dark current of the device is reduced.

Claims

1. A high temperature infrared detector with improved potential barrier, characterized in that: include: Substrate, buffer layer, N-type long-wave absorption layer, improved superlattice barrier layer, N-type ohmic contact layer; The buffer layer is epitaxially grown on the substrate, the N-type long-wave absorption layer is epitaxially grown on the buffer layer, the improved superlattice barrier layer is epitaxially grown on the N-type long-wave absorption layer, and the N-type ohmic contact layer is epitaxially grown on the improved superlattice barrier layer; The improved superlattice barrier layer should cover the space charge region of the heterojunction formed by the N-type long-wave absorption layer and the N-type ohmic contact layer; The substrate is GaSb, The buffer layer has a thickness of 500nm-1000nm and is composed of Si-doped InAsSb with a Si doping concentration of 1×10 17 cm -3 ~1×10 18 cm -3 ; The N-type long-wave absorption layer has a thickness of 3-6 μm and is composed of a Si-doped InAs / InAsSb superlattice, each period of which is composed of 25-30 ML InAs and 5-7 ML InAsSb, and the Si doping concentration is 1×10 16 cm -3 ~1×10 17 cm -3 ; The improved superlattice barrier layer has a thickness of 400nm-500nm and is composed of undoped InAs / AlAs / InAs / InAsSb superlattice, wherein each period is composed of 12-16ML InAs, 1-2ML AlAs, and 5-7ML InAsSb, wherein the thickness of the InAsSb layer in each period is the same as the thickness of the InAsSb layer in each period of the N-type long-wave absorption layer; The N-type ohmic contact layer has a thickness of 200-400 nm and is composed of a Si-doped InAs / InAsSb superlattice, each period of which is composed of 25-30 ML InAs and 5-7 ML InAsSb, and the Si doping concentration is 1×10 17 cm -3 ~1×10 18 cm -3 .

2. A high temperature infrared detector with improved potential barrier according to claim 1, characterized in that: Also includes: A first electrode and a second electrode, wherein the first electrode is disposed on the buffer layer, and the second electrode is disposed on the N-type ohmic contact layer.

3. A method for manufacturing a high temperature infrared detector with improved potential barrier as claimed in claim 1, characterized in that the steps include: S1: forming a buffer layer, an N-type long-wave absorption layer, a modified superlattice barrier layer, and an N-type ohmic contact layer stacked in sequence on a substrate by epitaxial growth; S2: forming a mesa consisting of the N-type long-wave absorption layer, the improved superlattice barrier layer, and the N-type ohmic contact layer on the buffer layer; S3: establishing a first electrode and a second electrode on the surface of the buffer layer and the surface of the N-type ohmic contact layer, respectively.

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