WO2023000272A1 - 一种高增益光电探测器 - Google Patents

一种高增益光电探测器 Download PDF

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WO2023000272A1
WO2023000272A1 PCT/CN2021/107953 CN2021107953W WO2023000272A1 WO 2023000272 A1 WO2023000272 A1 WO 2023000272A1 CN 2021107953 W CN2021107953 W CN 2021107953W WO 2023000272 A1 WO2023000272 A1 WO 2023000272A1
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layer
quantum structure
gain
periodic
emitter
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French (fr)
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江灏
吕泽升
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中山大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/11—Devices sensitive to infrared, visible or ultraviolet radiation characterised by two potential barriers, e.g. bipolar phototransistors

Definitions

  • the present invention relates to the technical field of semiconductor photodetectors, more specifically, to a high-gain photodetector.
  • Photodetectors are widely used in optical communication, imaging, environmental monitoring, assisted driving and various experimental tests. For photodetectors, responsivity is a very important index. High-responsivity semiconductor photodetectors with internal gain can realize high-sensitivity detection of weak light signals at room temperature and low bias voltage, and can save additional The signal amplifier makes the photoelectric detection system more compact, portable and low cost.
  • the n-p-n type phototransistor is a commonly used semiconductor photodetector with internal gain. The principle of photoelectric gain is that when the base region is suspended, the holes generated by light absorption in the collector junction will be under the action of the built-in field and the external electric field. The drift to the base produces accumulation, which leads to a lowering of the emitter junction barrier, causing electron injection at the emitter, thereby generating a photoinduced current with internal gain.
  • heterojunction phototransistor which uses a wider bandgap emitter material to design the emitter junction as a heterojunction, thereby blocking the diffusion of holes, improving the electron injection ratio and The effect of transistor magnification.
  • the present invention aims at overcoming at least one defect (deficiency) of the above-mentioned prior art, and provides a high-gain photodetector capable of obtaining low dark current, higher responsivity, extremely weak light detection capability, and high-speed response Effect.
  • a high-gain photodetector comprising an emitter, a base, an absorption layer, and a collector sequentially arranged from bottom to top, and also includes a periodic quantum structure layer, and the periodic quantum structure layer is arranged on the emitter and the collector between, or inside the base, or inside the emitter;
  • the periodic quantum structure layer includes multiple periods of repeated structures, and each period contains a semiconductor heterostructure, thereby forming multiple valence band steps and corresponding hole potential wells and potential barriers. Among them, a semiconductor junction formed by two adjacent heterogeneous materials is a heterojunction.
  • the emitter, base, absorption layer and collector constitute the main device structure of the phototransistor.
  • the electron injection ratio and device magnification are improved, and provide Superimposed photoconductive gain to obtain higher responsivity.
  • the hole lifetime can be adjusted by controlling its structural parameters, so as to achieve high gain while ensuring the response speed of the device.
  • the periodic quantum structure layer uses a periodic quantum structure to form a series of valence band hole barriers to block the diffusion of holes from the base to the emitter, and there is no conduction band electron barrier or electron barrier in the structure
  • the thickness allows the direct tunneling of electrons with smaller effective mass, so it does not affect the diffusion of electrons from the emitter to the base, so that the electron injection ratio of the emitter of the phototransistor can be improved and the magnification of the transistor can be increased.
  • the periodic quantum structure since the periodic quantum structure includes multiple valence band levels, the effect of hindering the diffusion of holes will be better than that of a heterojunction phototransistor structure with a single valence band level, that is, it can provide higher Electron injection ratio and magnification.
  • the periodic quantum structure blocks the diffusion of the base holes to the emitter, it will trap a part of the photogenerated holes in the hole potential well of the device structure, and the lifetime of the holes in the potential well will be affected by thermal emission and tunneling.
  • the probability of its escape from the quantum well depends on the depth of the hole potential well and the thickness of the hole barrier.
  • the depth of the hole potential well (the difference between the valence band and band order) can be adjusted by selecting different heterogeneous semiconductor materials, and the thickness of the hole barrier can be directly controlled by the material thickness of each layer in the periodic structure. Therefore, by changing these structural parameters, the hole lifetime can be regulated, so that the hole lifetime exceeds the electron transit time, and superimposed photoconductive gain is obtained to further improve the responsivity of the detector.
  • the photoconductive gain mechanism of the present invention is: through the periodic quantum structure, a series of hole potential wells are formed to obtain the effect of hole confinement, so that the lifetime of holes is higher than the time required for electron transit, so that photogenerated electrons transit to After the electrode is collected, because the holes are still bound in the quantum structure, the cathode continues to emit electrons to maintain electrical neutrality. After many cycles, the photoelectron current collected by the phototransistor is much higher than that collected directly for the first time. Photoelectron current, thus forming the effect of photocurrent gain, where the gain multiple is the ratio of hole lifetime to electron transit time.
  • the periodic quantum structure layer can be interposed between the emitter and the collector, and can also be embedded inside the base or inside the emitter.
  • the hole lifetime can be controlled by the depth of the hole potential well in the periodic structure (the size of the valence band, depending on the material used) and the thickness of each layer, so as to realize the regulation of the response speed of the detector and obtain high gain while realizing high-speed response.
  • the periodic quantum structure layer has a hole potential well layer and a hole barrier layer formed by heterostructure valence bands. Further, the depth of the hole potential well is higher than 3kT; wherein, k is a Boltzmann constant, and T is an operating temperature. When the potential well depth is less than 3kT, holes can easily escape from the potential well layer through thermal emission, resulting in the failure of the hole confinement effect of the periodic quantum structure.
  • the hole potential well formed in the quantum structure is obtained through the valence band of the heterostructure, so it has a strong binding effect on holes, but there may be no potential well for electrons, or there may be electron potential wells, but by adjusting the thickness, electrons can pass through the tunnel. Tunneling and escaping from the potential well of electrons means that the effective mass of electrons is smaller than that of holes, and tunneling is easier to occur, so the binding effect on electrons is weak.
  • the probability of electrons escaping from the electron potential well layers is higher than that of holes in the hole potential well layers. Probability, that is, the binding effect of the electron potential well on the electron is relatively weak, so the time required for the electron to cross is still shorter than the hole lifetime. Therefore, a high gain effect can also be obtained.
  • the thickness of the electronic barrier layer in the periodic quantum structure should not exceed the de Broglie wavelength of electrons in the electronic potential well layer; when the thickness of the periodic quantum structure When the wavelength is shorter than that of electrons, electrons can tunnel through, and the barrier effect is weak, so that the entire periodic quantum structure layer will bind holes more strongly than electrons, so that the time required for electrons to transit is shorter than the lifetime of holes .
  • the period number of the periodic quantum structure layer is ⁇ 3. If the number of cycles is too small, the binding effect on holes will be weakened, the photoconductive gain will not be significant, and the electron injection ratio and transistor amplification will also be reduced.
  • the periodic quantum structure layer is a quantum well layer.
  • the periodic quantum structure layer is a superlattice layer.
  • the quantum well layer or the superlattice layer forms a series of valence band steps, which act as a hole potential well, so that the holes are trapped in the potential well, thereby prolonging the hole lifetime t1 and exceeding the electron transit time t2, to form the effect of photoconductive gain.
  • the magnitude of the photoconductive gain is t1/t2.
  • the periodic quantum structure of the technical solution can also be other structures that can form hole-trapping effects, for example, a structure with only hole potential wells but no electron potential wells.
  • the periodic quantum structure is one of AlGaN/GaN superlattice structure, AlGaN/GaN multiple quantum well structure, AlGaAs/GaAs superlattice structure, AlGaAs/GaAs multiple quantum well structure.
  • upper and lower contact electrodes are also included.
  • an ohmic contact is formed between the upper contact electrode and the collector electrode, and the lower contact electrode and the emitter electrode, or the height of the contact potential barrier is lower than 0.5 eV, so as to avoid reducing the photocurrent of the device.
  • the lower contact electrode and the upper contact electrode are Ti/Al/Ni/Au or Au/AuGeNi alloy.
  • the emitter and the collector are n-type conductive semiconductor materials, and the electron concentration is higher than 5 ⁇ 10 16 cm -3 .
  • the emitter is n-type AlGaN or n-type AlGaAs or n-type GaN.
  • the collector is n-type GaN or n-type GaAs
  • the low electron concentration of the emitter will lead to the decrease of the photocurrent.
  • the base is a p-type conductive semiconductor material, and the hole concentration is higher than 1 ⁇ 10 16 cm -3 .
  • the too low hole concentration in the base region will also lead to early punch-through of the base region and increase the dark current.
  • the base is a p-type GaN layer.
  • the absorption layer is an intrinsically or unintentionally doped semiconductor material, and the hole or electron concentration is lower than 5 ⁇ 10 17 cm -3 .
  • too high carrier concentration in the absorbing layer will lead to a decrease in the width of the depletion layer, a decrease in the collection efficiency of photogenerated carriers, and a deterioration in the detector responsivity.
  • the absorption layer is unintentionally doped GaN or unintentionally doped GaAs.
  • This technical solution adds a periodic quantum structure layer to the device structure, so that the photogenerated electron holes are transported/moved, and the holes are bound, so that the electrode injects more electrons to form a current gain and obtain a high gain effect. .
  • the technical solution realizes the effect of photoelectric high gain on the basis of not introducing trap states, not deteriorating the response speed of the device, and the speed is controllable.
  • the diffusion of holes from the base to the emitter is blocked, and the diffusion of electrons from the emitter to the base is not affected, thereby increasing the electron injection ratio of the phototransistor and increasing the magnification of the transistor .
  • the present invention introduces a superimposed speed-controllable photoconductive gain on the basis of the phototransistor, which can not only make up for the weak light response of the phototransistor, but also further improve the overall gain; it can operate at low bias voltage without demanding material crystal quality.
  • the beneficial effects of high-speed and extremely high-responsivity photodetection can be achieved under the same conditions.
  • the invention forms a series of hole potential wells and potential barriers by introducing a periodic quantum structure to regulate the transport of photogenerated electrons and holes, thereby superimposing photoconductive gain on the photoinduction mechanism of the phototransistor.
  • the periodic quantum structure of the present invention can prevent base holes from diffusing to the emitter, improve the electron injection ratio of the emitter junction and the magnification of the transistor, and on the other hand, can bind holes with greater effective mass in the multilayer quantum structure.
  • the recombination loss is reduced in the structure, and the lifetime of the hole in the device exceeds the transport time of the electron, resulting in a superimposed photoconductive gain in the phototransistor.
  • the hole lifetime can be controlled through the material selection and thickness ratio of the periodic structure, so as to realize the regulation of the response speed of the detector, and achieve high-speed response while obtaining high photoelectric gain.
  • Fig. 1 is a schematic structural diagram of Embodiment 1 of the present invention.
  • Fig. 2 shows the energy band simulation results of the periodic quantum structure (AlGaN/GaN superlattice) in Example 1 of the present invention, and conduction band electrons and valence band holes escape through thermal emission (TE) and tunneling (T) Schematic diagram of the potential well process.
  • TE thermal emission
  • T tunneling
  • Fig. 3 is a schematic structural diagram of Embodiment 4 of the present invention.
  • Fig. 4 is a schematic structural diagram of Embodiment 6 of the present invention.
  • FIG. 5 is a test result of the photo-dark current characteristic of the photodetector in Example 1 of the present invention.
  • FIG. 6 is the test result of the response speed of the photodetector in Embodiment 1 of the present invention.
  • a GaN-based high-gain photodetector structure mainly includes an emitter layer 201, a periodic quantum structure layer 202, a base layer 203, an absorption layer 207, and a collector layer arranged in sequence from bottom to top. 204.
  • lower contact electrodes 205 are provided on both sides of the upper surface of the emitter layer 201
  • upper contact electrodes 206 are provided on both sides of the upper surface of the absorber layer 205 .
  • the material of the emitter layer 201 is n-type AlGaN, the Al composition is 20%, the electron concentration is 2 ⁇ 10 18 cm ⁇ 3 , the thickness is 300 nm, and the preparation method is not limited. Specifically, a substrate layer and/or a buffer layer is further provided under the emitter layer.
  • the periodic quantum structure layer 202 is an AlGaN/GaN superlattice structure, in which the Al component is 20%, the number of periods is 20, the thickness of the AlGaN layer in each period is 2nm, and the thickness of GaN is 4nm.
  • the base layer 203 is a p-type GaN layer with a hole concentration of 1 ⁇ 10 18 cm ⁇ 3 and a thickness of 100 nm.
  • the preparation method and doping method are not limited.
  • the collector layer 204 is n-type GaN with an electron concentration of 5 ⁇ 10 17 cm ⁇ 3 and a thickness of 120 nm.
  • Both the lower contact electrode 205 and the upper contact electrode 206 are Ti/Al/Ni/Au with a thickness of 15/80/20/60 nm.
  • the absorption layer 207 is unintentionally doped GaN with a thickness of 150 nm.
  • TE thermal emission
  • T tunneling
  • the carrier lifetime ⁇ will be mainly determined by the escape mechanism, namely: Among them, the carrier tunneling lifetime can be written as the carrier velocity according to the WKB approximate theory in quantum mechanics and the tunneling probability (T(E n )) relationship:
  • thermal emission lifetime ( ⁇ TE ) mainly depends on the effective barrier height:
  • Lw represents the thickness of the quantum well
  • E c, vmax represents the larger value of the potential energy of the electron and hole barrier
  • E n is the subband energy level height of the AlGaN quantum well, which can be written as:
  • the escape lifetimes of electrons and holes can be obtained as 1.4 ⁇ 10 -11 s and 8.3 ⁇ 10 -8 s, respectively. From the calculation results, it can be found that the escape lifetime of electrons in the quantum structure of this embodiment is much shorter than that of holes, that is, it is easier for electrons to escape from the quantum well. Furthermore, the equivalent mobility and drift velocity of electrons in the periodic structure can be calculated through the above process, so as to calculate the transit time of electrons. The calculated electron transit time in this structure is about 4.9 ⁇ 10 -9 s, so the resulting superimposed photoconductive gain is about 17 times.
  • the device can achieve a high-speed response of ns level while obtaining higher gain.
  • the difference between this embodiment and Embodiment 1 lies in that the material of the emitter layer is n-type GaN, the periodic quantum structure layer is AlGaN (6nm)/GaN (3nm) multiple quantum wells, and the number of periods is 10.
  • Embodiment 1 lies in that in the AlGaN/GaN superlattice layer of the periodic quantum structure layer, the Al composition of AlGaN is 15%, the thickness of AlGaN in each period is 3nm, and the thickness of GaN is 4nm.
  • a GaN-based high-gain photodetector structure mainly includes an emitter layer 301, a base layer 3031, a periodic quantum structure layer 302, and a base layer 3032 arranged sequentially from bottom to top.
  • absorber layer 307 and collector layer 304 are arranged sequentially from bottom to top.
  • Lower contact electrodes 305 are arranged on both sides of the upper surface of the emitter layer 301
  • upper contact electrodes 306 are arranged on both sides of the upper surface of the absorber layer 305 .
  • the base layer is divided into a base layer 1 3031 and a base 2 layer 3032, and the periodic quantum structure layer 302 is located in the base layer. That is, it is between the first base layer 3031 and the second base layer 3032 , as shown in FIG. 3 .
  • the periodic quantum structure layer is composed of 15 overlapping layers of AlGaN/GaN, wherein the thickness of GaN in each period is 4nm, and AlGaN includes 3 kinds of thickness: among them, from top to bottom Looking at the downward direction, in the first five periods of the periodic quantum structure layer, the thickness of each layer of AlGaN is 1.5nm, in the middle five periods, the thickness of each layer of AlGaN is 2.5nm, in the bottom five periods, the thickness of each layer of AlGaN is 4nm.
  • the hole barrier layer is an AlGaN layer, and the closer to the base region, the thinner the hole barrier is, which is conducive to the diffusion of more holes into the periodic quantum structure and improves the photoconductive gain effect;
  • the hole barrier closer to the emitter is thicker, which is beneficial to prevent the diffusion of holes into the emitter, and maintain a higher electron injection ratio and transistor magnification.
  • this embodiment shows a GaAs-based high-gain photodetector, which mainly includes an emitter layer 401, a periodic quantum structure layer 402, a base layer 403, and an absorption layer 407 arranged in sequence from bottom to top. and collector layer 404 .
  • Lower contact electrodes 405 are arranged on both sides of the upper surface of the emitter layer 401
  • upper contact electrodes 406 are arranged on both sides of the upper surface of the absorber layer 405 .
  • the material of the emitter layer 401 is n-type AlGaAs, the Al composition is 20%, the electron concentration is 2 ⁇ 10 18 cm ⁇ 3 , and the thickness is 300 nm.
  • the periodic quantum structure layer 402 is an AlGaAs/GaAs superlattice structure, in which the Al component is 20%, the number of periods is 20, the thickness of the AlGaN layer in each period is 4nm, and the thickness of GaN is 6nm.
  • the base 403 is a p-type GaN layer with a hole concentration of 1 ⁇ 10 18 cm ⁇ 3 and a thickness of 100 nm.
  • the collector electrode 404 is n-type GaAs with an electron concentration of 5 ⁇ 10 17 cm ⁇ 3 and a thickness of 120 nm.
  • Both the lower contact electrode 405 and the upper contact electrode 406 are Au/AuGeNi alloy.
  • the absorption layer 407 is unintentionally doped GaAs with a thickness of 200nm.
  • the photodetector prepared in Example 1 is characterized for detector characteristics.
  • the photodark current test results of the photodetector described in Example 1 under a low bias voltage of 10V, the photocurrent gain of the detector is as high as 1.3 ⁇ 10 5 .
  • the photodetector without the AlGaN/GaN superlattice in Example 1 has a gain of 6.5 ⁇ 10 4 under the same conditions.
  • the photoelectric gain of the device is increased by about 20 times, which is also consistent with the implementation The calculation results in Example 1 are roughly consistent.
  • the response speed test results of the device prepared in Example 1 are 2.4ns and 500ns respectively, which is far faster than the response of common photoconductive detectors exceeding the order of ms speed. It can be seen that the solution provided by the present invention can obtain a very fast response speed while improving the device responsivity.
  • the photodetector obtained by the present invention has the effects of high photoelectric gain and high response speed.

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Abstract

本发明公开了一种高增益光电探测器，包括从下到上依次设置的发射极、基极，吸收层和集电极，还包括周期性量子结构层，所述周期性量子结构层设置于发射极和集电极之间，或设置于基极的内部，或设置于发射极的内部；所述周期性量子结构层包括多个周期的重复结构，且每个周期内含有半导体异质结。本发明的周期性量子结构一方面能够阻挡基极空穴向发射极扩散，提高发射结的电子注入比和晶体管的放大倍数，另一方面可以将有效质量更大的空穴束缚于多层量子结构中而降低复合损失，并使器件中空穴寿命超过电子的输运时间，从而在光电晶体管中产生叠加的光电导增益。

Description

一种高增益光电探测器 技术领域
本发明涉及半导体光电探测器的技术领域，更具体地，涉及一种高增益光电探测器。
背景技术
光电探测器在光通信、成像、环境监控、辅助驾驶以及各种实验测试中都有着非常广泛的应用。对于光电探测器来说，响应度是非常重要的指标，有内部增益的高响应度半导体光电探测器可以在常温、低偏压下实现对微弱光信号的高灵敏度探测，同时可以省去附加的信号放大器，使得光电探测系统更加精简轻便，成本低廉。n-p-n型光电晶体管是一种常用的有内部增益的半导体光电探测器,其光电增益原理在于：基区悬空状态下，集电结中光吸收产生的空穴会在内建场和外加电场作用下漂移至基极产生累积，导致发射结势垒降低，引起发射极电子注入，从而产生有内部增益的光诱导电流。
在此基础上，另一种常用的改善结构是异质结光电晶体管，采用更宽禁带的发射极材料将发射结设计为异质结，从而起到阻挡空穴扩散，提高电子注入比和晶体管放大倍数的效果。
然而目前的光电晶体管和异质结光电晶体管仍有不足之处，例如对于微弱光信号，甚至单光子入射条件，光生空穴数量极为有限，很难对发射结势垒高度产生显著影响，因此会限制光电晶体管对于极微弱光的探测。而其他常见的探测器内部增益机理，也都有着各自的限制，例如：雪崩光电探测器要求材料缺陷密度很低以避免提前击穿，且需要较高的工作电压；光电导探测器暗电流较高，且一般有陷阱态参与的不可控的增益过程，会严重劣化探测器的响应速度，导致器件虽然能获得高响应度，但响应速度一般在毫秒甚至秒的量级，应用范围受到严重限制。
发明内容
本发明旨在克服上述现有技术的至少一种缺陷(不足)，提供一种高增益光电探测器，具有获得低暗电流、更高响应度，且具备极微弱光探测能力，以及高速响应的效果。
本发明采取的技术方案是：
一种高增益光电探测器，包括从下到上依次设置的发射极、基极、吸收层和集电极，还包括周期性量子结构层，所述周期性量子结构层设置于发射极和集电极之间，或设置于基极的内部，或设置于发射极的内部；
所述周期性量子结构层包括多个周期的重复结构，且每个周期内含有半导体异质结构，从而形成多重价带带阶以及对应的空穴势阱和势垒。其中，相邻两种异质材料形成的半导体结即是异质结。
本技术方案中，发射极、基极、吸收层和集电极组成了光电晶体管的主要器件结构，通过在主要器件结构上增加周期性量子结构层，以提高电子注入比和器件放大倍数，并提供叠加的光电导增益，来获得更高的响应度。同时，由于此叠加光电导增益来源于周期性量子结构而非陷阱态，可以通过控制其结构参数来对空穴寿命进行调控，从而在实现高增益的同时保证器件的响应速度。具体地，周期性量子结构层利用周期性量子结构，形成一系列的价带空穴势垒来阻挡空穴从基极向发射极的扩散，且结构中没有导带电子势垒或电子势垒厚度允许有效质量更小的电子直接隧穿通过，因此可以不影响电子从发射极向基极扩散，从而可以提高光电晶体管的发射极电子注入比和提高晶体管放大倍数。另外，由于周期性量子结构包括多重价带带阶，对空穴的扩散阻碍效果将更优于单一价带带阶的异质结光电晶体管结构，即可以提供比异质结光电晶体管更高的电子注入比和放大倍数。
更进一步地，周期性量子结构在阻挡基极空穴向发射极扩散的同时，会将一部分光生空穴束缚在器件结构的空穴势阱里，势阱中空穴的寿命将受到热发射和隧穿等逃逸机制的影响，其逸出量子阱的几率取决于空穴势阱的深度和空穴势垒的厚度。通过选择不同的异质半导体材料可以调控空穴势阱的深度(价带带阶差异大小)，而空穴势垒的厚度可以直接由周期结构中各层的材料厚度控制。因此，改变这些结构参数即可对空穴寿命进行调控，使得空穴寿命超过电子渡越时间，获得叠加的光电导增益，进一步提高探测器的响应度。
而由于周期性量子结构中空穴寿命可以由结构参数调控，因此可以避免空穴寿命过长导致的响应速度降低，在实现高光电增益的同时获得高速响应。
其中，本发明的光电导增益机理为：通过周期量子结构，形成一系列的空穴势阱，获得空穴束缚效果，使得空穴寿命高于电子渡越需要的时间，这样光生电子渡越到电极被收集之后，由于空穴仍被束缚在量子结构中，从而使阴极继续发射电子维持电中性，如此循环多次后，光电晶体管收集到的光电子电流远高于第一次直接收集到的光电子电流，从而形成光电流增益的效果，其中，增益倍数为空穴寿命与电子渡越时间的比值。
进一步地，周期量子结构层可以介于发射极和集电极之间，也可以嵌入基极内部或发射极内部。
进一步地，可以通过周期结构中空穴势阱的深度(价带带阶大小，取决于所用材料)和各层的厚度来控制空穴寿命，从而实现对探测器响应速度的调控，在获得高增益的同时实现高速响应。
进一步地，所述周期性量子结构层中存在异质结构价带带阶形成的空穴势阱层和空穴势垒层。进一步地，空穴势阱的深度高于3kT；其中，k是玻尔兹曼常量，T是工作温度。势阱深度小于3kT时空穴很容易通过热发射逃逸出势阱层，导致周期性量子结构的空穴束缚作用失效。
量子结构中形成的空穴势阱通过异质结构的价带带阶得到，因此对空穴束缚作用强，但对电子可以没有势阱，或有电子势阱但通过调控厚度可以让电子通过隧穿逃逸出电子势阱，即使得电子有效质量比空穴小，更容易发生隧穿，因而对电子束缚作用很弱。
在另一个实施例中，周期性量子结构层中同时存在电子势阱层和电子势垒层，且电子从电子势阱层中逸出的几率高于空穴中空穴势阱层中逸出的几率，即电子势阱对电子的束缚作用比较弱，这样，电子渡越需要的时间仍然小于空穴寿命。因此，也能获得高增益的效果。
具体地，周期量子结构层中若存在电子势阱和电子势垒，则周期量子结构中电子势垒层厚度应不超过电子势阱层中电子的德布罗意波长；当周期量子结构的厚度短于电子波长的时候，电子可以隧穿通过，阻碍作用弱，这样整个周期性量子结构层对空穴的束缚作用将强于对电子的束缚，从而使得电子渡越需要的时间小于空穴寿命。
进一步地，所述周期性量子结构层的周期数≥3。周期数过少对空穴的束缚作用减弱，光电导增益将不显著，同时电子注入比和晶体管放大倍数也会有所降低。
在其中一个实施例中，所述周期性量子结构层为量子阱层。
在另一个实施例中，所述周期性量子结构层为超晶格层。
量子阱层或超晶格层形成一系列的价带带阶，起到空穴势阱的作用，使得空穴被束缚于势阱中，从而使空穴寿命t1延长，且超过电子渡越时间t2，以形成光电导增益的效果。具体地，光电导增益的大小为t1/t2。
进一步地，本技术方案的周期性量子结构还可以为其它可以形成空穴束缚效果的结构，例如只有空穴势阱但没有电子势阱的结构。
进一步地，所述周期性量子结构为AlGaN/GaN超晶格结构、AlGaN/GaN多量子阱结构、 AlGaAs/GaAs超晶格结构、AlGaAs/GaAs多量子阱结构中的其中一种。
在其中一个实施例中，还包括上、下接触电极。
在其中一个实施例中，所述上接触电极与集电极、以及下接触电极与发射极之间，形成欧姆接触，或接触势垒的高度低于0.5eV，以避免降低器件的光电流。
进一步地，下接触电极和上接触电极为Ti/Al/Ni/Au或Au/AuGeNi合金。
在其中一个实施例中，所述发射极和集电极为n型导电半导体材料，电子浓度高于5×10 16cm -3。
进一步地，发射极为n型AlGaN或n型AlGaAs或n型GaN。集电极为n型GaN或n型GaAs
其中，发射极电子浓度过低会导致光电流降低。
在其中一个实施例中，所述基极为p型导电半导体材料，空穴浓度高于1×10 16cm -3。
其中，基极区的空穴浓度过低也会导致基极区提早穿通，暗电流升高。
进一步地，基极为p型GaN层。
在其中一个实施例中，所述吸收层为本征或非故意掺杂半导体材料，空穴或电子浓度低于5×10 17cm -3。
其中，吸收层的载流子浓度过高会导致耗尽层宽度减小，光生载流子收集效率降低，探测器响应度劣化。
进一步地，吸收层为非故意掺杂GaN或非故意掺杂GaAs。
与现有技术相比，本发明的有益效果为：
本技术方案通过在器件结构上增加周期性量子结构层，使得光生电子空穴的输运/移动过程中，束缚空穴，从而使电极注入更多电子，以形成电流增益，获得高增益的效果。
本技术方案在不引入陷阱态、不劣化器件响应速度、且速度可控的基础上，实现了光电高增益的效果。
本发明通过增加周期性量子结构层，实现了阻挡空穴从基极向发射极扩散的同时，且不影响电子从发射极向基极扩散，从而提高光电晶体管的电子注入比，提高晶体管放大倍数。
本发明在光电晶体管的基础上引入叠加的速度可控的光电导增益，既可以弥补光电晶体管弱光响应的不足，又可以进一步提高整体增益；具有无需苛求材料晶体质量，即可在低偏压下实现高速和极高响应度光电探测的有益效果。
本发明通过引入周期性的量子结构来形成一系列的空穴势阱和势垒，以调控光生电子、空穴的输运，从而在光电晶体管的光诱导机制上叠加光电导增益。本发明的周期性量子结构 一方面能够阻挡基极空穴向发射极扩散，提高发射结的电子注入比和晶体管的放大倍数，另一方面可以将有效质量更大的空穴束缚于多层量子结构中而降低复合损失，并使器件中空穴寿命超过电子的输运时间，从而在光电晶体管中产生叠加的光电导增益。此外，在本发明提供的器件结构中，可以通过周期结构的材料选择和厚度配比来控制空穴寿命，从而实现对探测器响应速度的调控，在获得高光电增益的同时实现高速响应。
附图说明
图1为本发明实施例1的结构示意图。
图2为本发明实施例1中的周期型量子结构(AlGaN/GaN超晶格)的能带模拟结果，以及导带电子、价带空穴通过热发射(TE)和隧穿(T)逃逸势阱的过程示意图。
图3为本发明实施例4的结构示意图。
图4为本发明实施例6的结构示意图。
图5为本发明实施例1中光电探测器的光暗电流特性测试结果。
图6为本发明实施例1中光电探测器的响应速度测试结果。
具体实施方式
本发明附图仅用于示例性说明，不能理解为对本发明的限制。为了更好说明以下实施例，附图某些部件会有省略、放大或缩小，并不代表实际产品的尺寸；对于本领域技术人员来说，附图中某些公知结构及其说明可能省略是可以理解的。
实施例1
如图1所示，一种GaN基高增益光电探测器结构，主要包括从下到上依次设置的发射极层201、周期性量子结构层202、基极层203、吸收层207和集电极层204。
本实施例中，发射极层201的上表面两侧设有下接触电极205，吸收层205的上表面两侧设有上接触电极206。
其中，发射极层201的材料为n型AlGaN，Al组分为20％，电子浓度为2×10 18cm -3，厚度为300nm，制备方法不限。具体地，发射极层的下方还设有衬底层和/或缓冲层。
周期性量子结构层202为AlGaN/GaN超晶格结构，其中Al组分为20％，周期数为20，每个周期中AlGaN层厚度为2nm，GaN厚度为4nm。
基极层203为p型GaN层，空穴浓度为1×10 18cm -3，厚度为100nm，制备方法和掺杂方法不作限制。
集电极层204为n型GaN，电子浓度为5×10 17cm -3，厚度为120nm。
下接触电极205和上接触电极206都为Ti/Al/Ni/Au，厚度为15/80/20/60nm。
吸收层207为非故意掺杂GaN，厚度为150nm。
如图2所示是本实施例中AlGaN/GaN超晶格层的能带模拟结果和导带电子/价带空穴通过热发射(TE)和隧穿(T)逃逸电子势阱/空穴势阱的过程示意图。
由于量子限制斯塔克效应(quantum confined stark effect，QCSE)的影响，电子和空穴在空间上将会分离，波函数交叠量减少，导致电子与空穴的复合率很低，所以辐射复合寿命和非辐射复合寿命会很大。此时载流子寿命τ会主要由逃逸机制决定，即：
Figure PCTCN2021107953-appb-000001
其中，载流子隧穿寿命可以根据量子力学中的WKB近似理论，写为载流子速率
Figure PCTCN2021107953-appb-000002
和隧穿几率(T(E n))的关系式：
Figure PCTCN2021107953-appb-000003
而热发射寿命(τ TE)主要取决于有效势垒高度：
Figure PCTCN2021107953-appb-000004
式中L w代表量子阱的厚度，E c,vmax表示电子和空穴势垒电势能的较大值，E n为AlGaN量子阱的子带能级高度，可写为：
Figure PCTCN2021107953-appb-000005
采用模拟得到的能带形状带入上面三个公式进行计算，可以得到电子与空穴的逃逸寿命分别为1.4×10 -11s和8.3×10 -8s。通过计算结果可以发现本实施例的量子结构中电子的逃逸寿命远远短于空穴，即电子更容易逃逸出量子阱。进一步可以通过上述过程计算得到电子在周期结构中的等效迁移率和漂移速度，从而计算出电子的渡越时间。此结构中电子渡越时间计算结果大约为4.9×10 -9s，因此产生的叠加光电导增益约为17倍。
由于此结构中空穴寿命计算结果约为80ns，因此器件在获得更高增益的同时，也能达到ns级别的高速响应。
实施例2
本实施例与实施例1不同之处在于：发射极层的材料为n型GaN，周期量子结构层为 AlGaN(6nm)/GaN(3nm)的多量子阱，周期数为10。
实施例3
本实施例与实施例1不同之处在于：周期量子结构层的AlGaN/GaN超晶格层中，AlGaN的Al组分为15％，每个周期中AlGaN厚度为3nm，GaN厚度为4nm。
实施例4
如图3所示，一种GaN基高增益光电探测器结构，主要包括从下到上依次设置的发射极层301、基极一层3031、周期性量子结构层302、基极二层3032，吸收层307和集电极层304。发射极层301的上表面两侧设有下接触电极305，吸收层305的上表面两侧设有上接触电极306。
本实施例与实施例1不同之处在于：本实施例中，基极层被分为基极一层3031和基极二层3032，周期性量子结构层302的位置处于基极层之中，即处于基极一层3031和基极二层3032之间，如图3所示。
实施例5
本实施例与实施例1不同之处在于：周期量子结构层由15层AlGaN/GaN重复交叠组成，其中每个周期中GaN厚度为4nm，而AlGaN包括3种厚度：其中，以自上而下方向看，周期量子结构层的前5个周期中，每层AlGaN厚度为1.5nm，中间五个周期中，每层AlGaN厚度为2.5nm，最下方的五个周期中，每层AlGaN厚度为4nm。这样设置的周期性量子结构中，空穴势垒层为AlGaN层，越靠近基区的空穴势垒越薄，有利于更多空穴扩散进入到周期量子结构中，提高光电导增益效果；而越靠近发射极的空穴势垒越厚，有利于阻挡空穴扩散进入发射极，维持较高的电子注入比和晶体管放大倍数。
实施例6
如图4所示，本实施例展示了一种GaAs基高增益光电探测器，主要包括从下到上依次设置的发射极层401、周期性量子结构层402、基极层403，吸收层407和集电极层404。发射极层401的上表面两侧设有下接触电极405，吸收层405的上表面两侧设有上接触电极406。
发射极层401的材料为n型AlGaAs，Al组分为20％，电子浓度为2×10 18cm -3，厚度为300nm。
周期量子结构层402为AlGaAs/GaAs超晶格结构，其中Al组分为20％，周期数为20，每个周期中AlGaN层厚度为4nm，GaN厚度为6nm。
基极403为p型GaN层，空穴浓度为1×10 18cm -3，厚度为100nm。
集电极404为n型GaAs，电子浓度为5×10 17cm -3，厚度为120nm。
下接触电极405和上接触电极406都为Au/AuGeNi合金。
吸收层407为非故意掺杂GaAs，厚度为200nm。
实施例7
本实施例对实施例1制备的光电探测器进行探测器特性表征。
如图5所示是实施例1所述光电探测器的光暗电流测试结果，在10V的低偏压下，探测器的光电流增益高达1.3×10 5。而不包含实施例1中AlGaN/GaN超晶格的光电探测器相同条件下增益为6.5×10 4，显然，通过引入周期性量子结构，器件的光电增益提高了大约20倍，这也与实施例1中的计算结果大致吻合。
如图6所示是实施例1中制备器件的响应速度测试结果，测得的探测器上升时间和下降时间分别为2.4ns和500ns，远远快于常见光电导探测器超过ms量级的响应速度。可见，本发明提供的方案，在提高器件响应度的同时还可获得很快的响应速度。
同理，本实施例对实施例2～6制备的光电探测器进行光暗电流测试和相应速度测试后，得到了与实施例1一样光电增益提高和高响应速度的效果。因此，本发明获得的光电探测器具有高光电增益和高响应速度的效果。
显然，本发明的上述实施例仅仅是为清楚地说明本发明技术方案所作的举例，而并非是对本发明的具体实施方式的限定。凡在本发明权利要求书的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明权利要求的保护范围之内。

Claims (10)

  1. 一种高增益光电探测器，其特征在于，包括从下到上依次设置的发射极、基极，吸收层和集电极，还包括周期性量子结构层，所述周期性量子结构层设置于发射极和集电极之间，或设置于基极的内部，或设置于发射极的内部；
    所述周期性量子结构层包括多个周期的重复结构，且每个周期内含有半导体异质结。
  2. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述周期性量子结构层中存在异质结价带带阶形成的一系列空穴势阱层和空穴势垒层。
  3. 根据权利要求2所述的一种高增益光电探测器，其特征在于，所述周期性量子结构层中同时存在异质结导带带阶形成的一系列电子势阱层和电子势垒层，且电子从电子势阱层中逸出的几率高于空穴从空穴势阱层中逸出的几率。
  4. 根据权利要求2所述的一种高增益光电探测器，周期性量子结构中空穴势阱的深度高于3kT，其中，k是玻尔兹曼常量，T是工作温度；单个空穴势垒层的厚度不小于0.5nm。
  5. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述周期性量子结构层的周期数≥3。
  6. 根据权利要求1所述的一种高增益光电探测器，其特征在于，还包括上、下接触电极；
    所述上接触电极与集电极、以及下接触电极与发射极之间，形成欧姆接触，或接触势垒的高度低于0.5eV。
  7. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述发射极和集电极为n型导电半导体材料，电子浓度高于5×10 16cm -3。
  8. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述基极为p型导电半导体材料，空穴浓度高于1×10 16cm -3。
  9. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述吸收层为本征半导体或非故意掺杂半导体，电子和空穴的浓度都低于5×10 17cm -3。
  10. 根据权利要求1所述的一种高增益光电探测器，其特征在于，所述周期性量子结构层为量子阱层或超晶格层。
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CN105206702A (zh) * 2014-06-27 2015-12-30 中国人民解放军军械工程学院 一种新型结构的单光子探测器
CN109494275A (zh) * 2018-11-22 2019-03-19 中国科学院长春光学精密机械与物理研究所 一种AlGaN基日盲紫外光电晶体管探测器及其制作方法
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CN1773729A (zh) * 2005-09-23 2006-05-17 中国科学院上海技术物理研究所 自放大红外探测器
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