摘要
高速响应的中波红外探测器在自由空间光通信和频率梳光谱学等新兴领域的需求逐渐增加。中长波XBnn势垒型红外光探测器对暗电流等散粒噪声具有显著抑制作用。本文在GaSb衬底上采用分子束外延技术生长了nBn和pBn两种结构的InAsSb/AlAsSb/AlSb中波红外光探测器材料,并通过微纳加工工艺制备了可用于射频响应特性测试的GSG结构探测器。XRD和AFM的测试结果表明,两种结构的外延片都具有较好的晶体质量。器件暗电流测试结果表明,相较于nBn器件,在室温和反向偏压400 mV的工作条件下,直径90 μm的pBn器件表现出更低的暗电流密度0.145 A/cm²,说明该器件在室温非制冷环境下表现出较低的噪声水平。不同台面直径的探测器的暗电流测试表明,pBn器件的表面电阻率低于对照的nBn器件的表面电阻率。另外,根据探测器的电容测试结果,可零偏压工作的pBn探测器具有完全耗尽的势垒层和部分耗尽的吸收区,nBn的吸收区也存在部分耗尽。探测器的射频响应特性表明,直径90 μm的pBn器件的响应速度在室温和3 V反向偏压下可达2.62 GHz,对照的nBn器件的响应速度仅为2.02 GHz,响应速度提升了29.7%,初步实现了在中红外波段下可快速探测的室温非制冷势垒型光电探测器。
中波红外(3~5 μm)光电探测器在远距离成像、导弹制导等领域得到了广泛应用。自由空间光通信和频率梳光谱学等新兴领域对高速响应的红外光探测器的需求也逐渐增
在本工作中,我们制备了不同直径的nBn和pBn结构的中波InAsSb/AlAsSb红外接地-信号-接地(Ground-Signal-Ground, GSG)探测器,并对制备的探测器进行了变温暗电流特性、结电容特性和室温射频响应特性的表征测试。通过比较nBn和pBn器件的测试结果,我们发现直径90 μm的pBn器件在室温和反向偏压400 mV工作时,具有更低的暗电流密度(0.145 A/cm²)和更高的3 dB带宽(2.62 GHz)。
本文通过固态源分子束外延技术在2英寸的n型Te-GaSb衬底上分别外延生长nBn和pBn两种势垒型结构器件。生长过程如下所示:先在衬底上生长GaSb缓冲层来获得平整表面以及减少材料应力和位错,接着生长重掺杂的(1
图1 (a)为nBn和pBn外延片的X射线衍射谱;(b)和(d)分别为nBn和pBn外延片的原子力显微扫描图;(c)和(e)分别为制备的圆形GSG探测器的光学照片和扫描电子照片
Fig. 1 (a) X-ray diffraction spectra of nBn and pBn epitaxial wafers;(b) and (d) atomic force microscopic images for nBn and pBn epitaxial wafers;(c) and (e) optical and scanning electron micrographs of the fabricated circular GSG detector
, | (1) |
, | (2) |
其中,Ea和Φb分别是吸收层和电子势垒层的激活能,Vb为施加的偏置电压。T、q、kb和
图2 77~300 K温度下直径90 μm的nBn和pBn探测器单管芯片:(a)暗电流密度-电压曲线;(b)微分电阻和器件面积的乘积R0A随反向偏压的变化曲线;(c) R0A随1000/T的变化曲线
Fig. 2 (a) Dark current density-voltage curves;(b) differential resistance and device area product (R0A) versus reverse bias;(c) Arrhenius plot of R0A at -400 mV for 90 μm nBn and pBn detector single-element chips at temperatures ranging from 77 K to 300 K
由于势垒型红外探测器对于体内暗电流可以起到较好的抑制作用,因此我们关注与台面周长和面积有关的表面泄露暗电流。通过抑制表面漏电流可以进一步提高探测器的工作性能。
图3 20~100 μm直径的nBn和pBn器件于室温下的(a)暗电流密度和电压变化曲线和(b) R0A随反向偏压的变化曲线;(c) 在400 mV反偏时,pBn和nBn器件R0A随台面直径的变化;(d) (R0A
Fig. 3 (a) Dark current density-voltage curves of nBn and pBn devices with diameters ranging from 20 μm to 100 μm at room temperature;(b) variation curves of R0A with reverse bias;(c) R0A varied with mesa diameters for pBn and nBn devices at a reverse bias of 400 mV;(d) variation of (R0A
, | (3) |
其中,(R0A)bulk为去除表面泄漏影响后,探测器的体积微分电阻和台面面积的乘积,ρsurface为探测器的表面电阻率。P为台面周长,A为台面面积。随着台面尺寸增加,P/A减小,侧壁上的表面缺陷带来的钉扎效应降低,因此器件通过表面导电通道导致的泄露电流的占比逐渐降低。
图4 (a)室温下不同直径的nBn和pBn探测器的结电容随反向偏压的变化曲线;(b)反偏400 mV下结电容与台面直径的变化曲线
Fig. 4 (a) Junction capacitance versus reverse bias for nBn and pBn detectors with different diameters at room temperature;(b) variation in junction capacitance with mesa diameters at a reverse bias of 400 mV
, | (4) |
其中,Ctotal是总电容,Cdep是InAsSb耗尽区的电容,Cbar是势垒层的电容。在反向偏置条件下,InAsSb的耗尽主要发生在势垒层的吸收区侧,其电容表达式为:
, | (5) |
其中,ε0为自由空间介电常数,εdep和εbar分别是InAsSb和AlAsSb/AlSb的相对介电常数,A是器件面积,ddep和dbar为InAsSb耗尽区和势垒层的厚度。其中,ε0、εdep、εbar、dbar和A均为常数,ddep是随着施加的反向偏压变化的变量。
通过Keysight PNA-X N5247B矢量网络分析仪、探针台和飞秒激光光源,在0~3 V反向偏压范围内对不同尺寸的nBn和pBn探测器在10 MHz~67 GHz之间进行了室温射频响应特性测试。根据
图5 在300 K下施加-3 V偏压的40 μm、50 μm、70 μm、80 μm、90 μm和100 μm直径的nBn和pBn探测器的归一化频率响应特性
Fig. 5 The normalized frequency response of 40 μm, 50 μm, 70 μm, 80 μm, 90 μm and 100 μm diameter nBn and pBn detectors with -3 V bias applied at 300 K
, | (6) |
, | (7) |
, | (8) |
其中,R为探测器电阻、C为探测器电容、vsat为饱和漂移速度、di为吸收区厚度。一般随着p-i-n探测器直径的增加,探测器的R和C都会增大,导致fRC减小以至总f3dB减小。但是
图6 不同尺寸的nBn和pBn探测器:(a) -3 dB截止频率随反向偏压的变化曲线;(b) 在3 V反向偏压下的-3 dB截止频率随台面直径的变化曲线
Fig. 6 nBn and pBn detectors with different sizes: (a) bias-dependent plot of -3 dB cutoff frequency;(b) variation of -3 dB cutoff frequency with mesa diameters at a reverse bias of 3 V
本文通过分子束外延技术在GaSb衬底上分别生长了nBn和pBn两种势垒型结构的InAsSb/AlAsSb/AlSb基中波红外光探测器,经过台面定义、钝化工艺和金属蒸镀工艺制备了可用于射频响应特性测试的GSG结构探测器。在室温和反向偏压400 mV下,直径90 μm的pBn器件的暗电流密度低于nBn器件。不同尺寸探测器的电学特性表征结果得到pBn器件的表面电阻率为1.7×1
5.27 Ω·c
References
Huang J, Shen Z, Wang Z, et al. High-Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector Based on InAs/InAsSb Type-II Superlattice[J]. IEEE Electron Device Letters, 2022, 43(5):745–748. [百度学术]
Peng R, Jiao S, Jiang D, et al. Investigation of dark current and differential resistance contributing mechanisms in type-II InAs/GaSb superlattice[J]. Journal of Materials Science: Materials in Electronics, 2016, 27(5):4566–4570. [百度学术]
Maimon S, Wicks G W. nBn detector, an infrared detector with reduced dark current and higher operating temperature[J]. Applied Physics Letters, 2006, 89(15):151109. [百度学术]
Klipstein P. "XB n " barrier photodetectors for high sensitivity and high operating temperature infrared sensors[C] // Andresen, B F; Fulop, G F; Norton, P R. Infrared Technology and Applications XXXIV. SPIE, 2008: 69402U. [百度学术]
Klipstein P, Klin O, Grossman S, et al. High operating temperature XBn-InAsSb bariode detectors[C] // Razeghi, M; Tournie, E; Brown, G J. Quantum Sensing and Nanophotonic Devices IX. SPIE, 2012: 82680U. [百度学术]
CHEN Dong-Qiong, WANG Hai-Peng, QIN Qiang, et al. Research on dark current characteristics of InAsSb Barrier blocking infrared detector[J]. J. Infrared Millim.Waves 陈冬琼, 王海澎, 秦强, 等.InAsSb势垒阻挡型红外探测器暗电流特性研究 [J]. 红外与毫米波学报, 2022, 41(5): 810-817. [百度学术]
Plis E, Rodriguez J B, Balakrishnan G, et al. Mid-infrared InAs/GaSb strained layer superlattice detectors with nBn design grown on a GaAs substrate[J]. Semiconductor Science and Technology, 2010, 25(8):85010. [百度学术]
Ting D Z, Soibel A, Khoshakhlagh A, et al. Development of InAs/InAsSb Type II Strained-Layer Superlattice Unipolar Barrier Infrared Detectors[J]. Journal of Electronic Materials, 2019, 48(10):6145–6151. [百度学术]
Klem J F, Kim J K, Cich M J, et al. Comparison of nBn and nBp mid-wave barrier infrared photodetectors[C] // Razeghi, M; Sudharsanan, R; Brown, G J. Quantum Sensing and Nanophotonic Devices VII. SPIE, 2010: 76081P. [百度学术]
Deng G, Yang W, Gong X, et al. High-performance uncooled InAsSb-based pCBn mid-infrared photodetectors[J]. Infrared Physics & Technology, 2020, 105:103260. [百度学术]
Deng G, Yang W, Zhao P, et al. High operating temperature InAsSb-based mid-infrared focal plane array with a band-aligned compound barrier[J]. Applied Physics Letters, 2020, 116(3):31104. [百度学术]
Deng G, Song X, Fan M, et al. Upside-down InAs/InAs1-xSbx type-II superlattice-based nBn mid-infrared photodetectors with an AlGaAsSb quaternary alloy barrier[J]. Optics express, 2020, 28(9):13616–13624. [百度学术]
Steenbergen E H. InAsSb-based photodetectors[M]//. Mid-infrared Optoelectronics. Elsevier, 2020: 415–453. [百度学术]
Henini M, Razeghi M. Handbook of infrared detection technologies[M]. Elsevier, 2002. [百度学术]
Huang E K, Hoffman D, Nguyen B-M, et al. Surface leakage reduction in narrow band gap type-II antimonide-based superlattice photodiodes[J]. Applied Physics Letters, 2009, 94(5):53506. [百度学术]
Kinch M A. State-of-the-art infrared detector technology[M]. Bellingham, Washington (1000 20th St. Bellingham WA 98225-6705 USA): SPIE, 2014. [百度学术]
Oehme M, Werner J, Kasper E, et al. High bandwidth Ge p-i-n photodetector integrated on Si[J]. Applied Physics Letters, 2006, 89(7):71117. [百度学术]
Wang Y, Nordin L, Dev S, et al. High-speed mid-wave infrared holey photodetectors[J]. Journal of Applied Physics, 2023, 133(10):104501. [百度学术]