HgCdTe光伏探测器反偏暗电流机制分析

HgCdTe光伏探测器在第二代和第三代红外探测器中处于主流地位.如何降低探测器的暗电流直接关系到探测器的噪声和灵敏度,其分析计算方法有多种.运用Synopsys半导体器件模拟软件对HgCdTepn结各种机制下的反偏暗电流和动态微分电阻进行了模拟计算.计算结果和相关文献报道的结果以及试验测试结果都吻合很好.     

n—HgCdTe光导器件两种表面钝化研究

利用Ａｒ＾＋束溅射沉积技术实现了ＣｄＴｅ薄膜的低温生长,利用电化学方法进行了ＨｇＣｄＴｅ表面自身阳极氧化膜的生长,利用生工的ＣｄＴｅ介质膜和ＨｇＣｄＴｅ表在身阳极氧化膜对ｎ－ＨｇＣｄＴｅ光导器件进行了表面钝化。对两种器件的电阻、各项性能指标进行了测量分析,实验表明得到的ＣｄＴｅ／ＨｇＣｄＴｅ同质量已达到器件实用化水平。     

HgCdTe光伏器件反常I—V特性分析

对ＨｇＣｄＴｅ光伏器件研制中出现的光电二极管伏安特性反常现象提出了寄生ｐ－ｎ结模型，并以此模型为基点，结合工艺实验对此现象进行了解释和分析。     

不同钝化结构的HgCdTe光伏探测器暗电流机制

在同一HgCdTe晶片上制备了单层ZnS钝化和双层(CdTe+ZnS)钝化的两种光伏探测器,对器件的性能进行了测试,发现双层钝化的器件具有较好的性能.通过理论计算,分析了器件的暗电流机制,发现单层钝化具有较高的表面隧道电流.通过高分辨X射线衍射中的倒易点阵技术研究了单双层钝化对HgCdTe外延层晶格完整性的影响,发现单层ZnS钝化的HgCdTe外延层产生了大量缺陷,而这些缺陷正是单层钝化器件具有较高表面隧道电流的原因.     

不同钝化结构的HgCdTe光伏探测器暗电流机制

在同一HgCdTe晶片上制备了单层ZnS钝化和双层（CdTe+ZnS）钝化的两种光伏探测器,对器件的性能进行了测试,发现双层钝化的器件具有较好的性能．通过理论计算,分析了器件的暗电流机制,发现单层钝化具有较高的表面隧道电流．通过高分辨X射线衍射中的倒易点阵技术研究了单双层钝化对HgCdTe外延层晶格完整性的影响,发现单层ZnS钝化的HgCdTe外延层产生了大量缺陷,而这些缺陷正是单层钝化器件具有较高表面隧道电流的原因．     

长波大面积HgCdTe光导红外探测器的研究

研制的长波大面积HgCdTe光导红外探测器的面积为2.1×2.1mm~2,在80K时探测率D_p~*=1.86×10~(10)cmHz~(1/2)W~(-1),响应率R_p=386VW~(-1),长波限λ_(co)(50%)>18μm.还研制了带有低温聚光器组合件结构的新型探测器,D_p~*=7.3×10~(10)cmHz~(1/2)W~(-1),λ_(co)(50%)>16μm.     

硅基HgCdTe光伏器件的暗电流特性分析

对硅基HgCdTe中波器件进行了变温电流电压特性的测试和分析。测量温度从30K到240K，得到R0对数与温度的1000／T的实验曲线及拟合结果。同时选取60K、80K及110K下动态阻抗尺与电压V的曲线进行拟合分析。研究表明在我们器件工作的温度点80K，零偏压附近主要的电流机制是产生复合电流和陷阱辅助隧穿电流。要提高器件的水平，必须降低陷阱辅助隧穿电流和产生复合电流对暗电流的贡献。     

HgCdTe光伏器件反常I－V特性分析

对ＨｇＣｄＴｅ光伏器件研制中出现的光电二极管伏安特性反常现象提出了寄生ｐ－ｎ结模型，并以此模型为基点，结合工艺实验对此现象进行了解释和分析。     

叠层HgCdTe光导器件载流子浓度分布及器件性能

根据Ｍ．Ａ．Ｋｉｎｃｈ提出了的叠层结构,从解一维连续性方程出发,对有叠层和无叠层器件光生载流子浓度空间分布进行了计算和分析,结果表明,叠层结构相当提供一个少数载流子存储区,可有效抑制扫出效应,提高体内光生载流子的平均浓度,从而提高响应率,实验上采用两种工艺实现了有叠层结构,并给出了器件性能的测量结果。     

High-Operating-Temperature HgCdTe Avalanche Photodiodes

In this communication we report the first results of electro-optical characterization of planar heterostructure HgCdTe avalanche photodiodes (APDs), which enables the operation of APDs at high gain, at low bias, and with low dark current and/or at high operating temperature (HOT). The APD is based on a heterostructure in which the photons are detected in a wide-band-gap layer, and the photoelectrons are amplified in a vertical junction in a confined narrow-gap layer. The dark diffusion current and thermal background sensitivity of the device are limited by using a thin narrow-band-gap amplification layer. In addition, the defect-limited dark current is also expected to be reduced due to the reduced volume of the narrow-band-gap depletion layer. The electro-optical performance was characterized at T = 80 K and T = 200 K for two devices with a nominal thickness of the amplification layer of w = 100 nm and 500 nm, realized in x _Cd = 0.3 Hg-vacancy-doped layers grown by molecular-beam epitaxy (MBE). The measurements show an average gain of 〈M〈 = 10 at a reverse bias of 5 V, which is slightly reduced compared with a conventional APD with x _Cd = 0.3. The thermal diffusion current measured at low reverse bias, V _b = 0.1 V, and at T = 200 K is about 0.1 mA/cm² to 0.3 mA/cm², which is a factor of 50 lower than standard x _Cd = 0.3 n-on-p APDs. The quantum efficiency due to absorption in the gain layer is high (QE_peak > 30%), although no antireflecting coating was used, indicating that the device can also be used for high-operating-temperature thermal detection.     

Characterization of HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiodes

This article reports new characterization data for large-area (250 μm ×  250 μm) back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiodes (e-APDs). These e-APDs were fabricated in p-type HgCdTe films grown by liquid-phase epitaxy (LPE) on CdZnTe substrates. We previously reported that these arrays exhibit gain that increases exponentially with reverse bias voltage, with gain-versus-bias curves that are quite uniform from element to element, and with a maximum gain of 648 at −11.7 V at 160 K for a cutoff wavelength of 4.06 μm. Here we report new data on these planar e-APDs. Data from a third LPE film with a longer cutoff wavelength (4.29 μm at 160 K) supports the exponential dependence of gain on cutoff wavelength, for the same bias voltage, that we reported for the first two films (with cutoffs of 3.54 μm and 4.06 μm at 160 K), in agreement with Beck’s empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Our lowest gain-normalized current density at 80 K and zero field-of-view is 0.3 μA/cm² at −10.0 V for a cutoff of 4.23 μm at 80 K. We report data for the temperature dependence of gain over 80 K to 200 K. We report, for the first time, the dependence of measured gain on junction area for widely spaced circular diodes with radii of 20 μm to 175 μm. We interpret the variation of measured gain with junction area in terms of an edge-enhanced electric field, and fit the data with a two-gain model having a lower interior gain and a higher edge gain. We report data for the excess noise factor F(M) near unity for gains up to 150 at 196 K. We describe the abrupt breakdown phenomenon seen in most of our devices at high reverse bias.     

Modeling and Design Considerations of HgCdTe Infrared Photodiodes under Nonequilibrium Operation

The general approach and effects of nonequilibrium operation of Auger suppressed HgCdTe infrared detectors are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to accurately model the devices, including self-consistent, steady-state solutions of Poisson’s equation and the carrier continuity equations for carrier densities, Boltzmann transport theory, and published models for recombination/generation processes in HgCdTe. Numerical simulations are used to optimize the material structure and doping levels for an Auger suppressed detector with λ _{c =} 5.5 μm at 200 K. The optimized detector structure with step doping and compositional profiles is then compared to a device with realistic gradient doping and compositional profiles.     

Modeling of LWIR HgCdTe Auger-Suppressed Infrared Photodiodes under Nonequilibrium Operation

The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to obtain self-consistent steady-state solutions of Poisson’s equation and the carrier continuity equations. Experimental current–voltage characteristics between 120 K and 300 K of HgCdTe Auger-suppressed photodiodes with cutoff wavelength of λ _c = 10 μm at 120 K are fitted using our numerical model. Based on this fitting, we study the lifetime in the absorber region, extract the current mechanisms limiting the dark current in these photodiodes, and discuss design and fabrication considerations in order to optimize future HgCdTe Auger-suppressed photodiodes.     

Nonequilibrium Operation of Arsenic Diffused Long-Wavelength Infrared HgCdTe Photodiodes

We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated a p-on-n structure that we term P ⁺/π/N ⁺ where the symbol “π” is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 10¹⁵ cm⁻³); P ⁺ and N ⁺ denote a higher doping density, as well as a higher energy gap, than the photosensitive base π-region. Fabricated devices indicated that Auger suppression is seen in the P ⁺/π/N ⁺ architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the π-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths of 7.4 μm and 10.4 μm, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination. Received November 7, 2007; accepted March 19, 2008     

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V _b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance–capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t _10–90 = 20 ps (at intermediate gains M < 500) and t _10–90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gain–bandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain–bandwidth product, GBW = 19 THz. The impulse response was modeled using a one-dimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v _e = 2.3 × 10⁷ cm/s and v _h = 1.0 × 10⁷ cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x _j = 4 μm and x _j = 2 μm, respectively, for a gain of M = 100.     

长波HgCdTe光导探测器液氮温度电阻和室温电阻比值计算

研究了长波ＨｇＣｄＴｅ光导探测器液搂温度电阻和室温电阻比值计算问题。结果表明：制成器件后，表面导导，材料电导率的变化和背景辐射都将使器件液氮温度的电阻减小，进行这三项修正后，器件电阻比值的计算值与实验值吻合。     

微型计算机的接触电流和接地线电流的测量

介绍了微型计算机的两种不同类型的泄漏电流的危害及其测量方法。     

背景辐射对光导HgCdTe探测器电阻的影响

测量了室温和液氮背景辐射条件下长波光导ＨｇＣｄＴｅｒ探测器的电阻，从电阻的变化研究了背景辐射对器件电阻的影响。结果表明：在高性能探测器中，室温背景辐射造成探测器电阻的相对变化量约为１０％，而且，该变化量与探测器性能有很好的对应关系。