1/f noise studies in uncooled narrow gap Hg1−xCdxTe non-equilibrium diodes

We have studied the 1/f noise current in narrow gap semiconductor heterostructure diodes fabricated in mercury cadmium telluride (HgCdTe) and designed to operate in a non-equilibrium mode at room temperature. HgCdTe heterostructure diodes exhibit Auger suppression giving current-voltage characteristics with high peak-to-valley ratios (up to 35), and low extracted saturation current densities (e.g., 20 Acnr⁻² at 10 pm at 295K) but high 1/f knee frequencies (e.g., 100 MHz at 10 μm at 295K). A comparison is made with the noise levels found in room temperature non-equilibrium mode heterostructure InAlSb/InSb diodes. The devices are being used at high frequencies for CO₂ laser heterodyne detector demonstrators. For the devices to be useful in low frame-rate imaging arrays, the 1/f noise level must be sufficiently low that the signal is not swamped. Ideally, the knee frequency should be below the frame rate. The relationship between the noise current and reverse bias voltage, current density, and temperature will be examined in order to attempt to identify the principal 1/f generation mechanisms.     

Minimally cooled heterojunction laser heterodyne detectors in metalorganic vapor phase epitaxially grown Hg1-xCdxTe

By taking advantage of Auger suppression techniques, the leakage currents of room temperature infrared detectors operating in the LWIR band can be greatly reduced. At present, these detectors suffer from large 1/f noise and hence the improvement in the detectivity resulting from the reduced leakage currents can only be realized at high frequencies. However, this is not a problem for heterodyne systems which employ intermediate frequencies above 40 MHz. A thermo-electrically cooled Auger suppressed infrared detector operated at 260K has been studied as a heterodyne detector. The device was operated with the application of sufficient local oscillator power to double its dark current (about 0.3 mW) and a NEP of 2 x 10^-19 W Hz⁻¹ was deduced from heterodyne measurements. The frequency response is presently limited by a combination of the detector capacitance and the series resistance to about 70 MHz and ways to reduce this series resistance are considered.     

碲镉汞光伏探测器的变面积表面钝化研究

利用同一片碲镉汞材料制备了由单层ZnS和双层CdTe/ZnS作钝化膜的变面积光伏探测器,对两种钝化膜结构的变面积器件进行了对比研究.通过分析两种器件的电流-电压(I-V)特性曲线以及零偏电阻-面积乘积(RoA)与周长-面积比(p/A)的关系曲线,发现ZnS钝化的器件具有较大的表面漏电流;通过分析两种器件的电流噪声与暗电流的关系,发现ZnS钝化的器件的噪声特性较接近散粒噪声,CdTe/ZnS双层钝化的器件则表现出较好的基本1/f噪声特性,使得器件噪声要小于单层ZnS钝化的器件.     

Recent results on metalorganic vapor phase epitaxially grown HgCdTe heterostructure devices

The ability to grow complex multilayer structures in Hg_1-xCd_xTe by epitaxial techniques has made it possible to produce a range of new devices such as infrared LEDs, lasers, and two-color infrared detector arrays. The devices described here, however, are designed to operate at temperatures above 145K and include both infrared sources and detectors. Three layer ppn structures, where the underlined symbols mean wider gap, have close to Auger limited R_oAs at temperatures above 145K. Under reverse bias, the devices exhibit Auger suppression leading to useful detectivities at room temperature. The diodes exhibit forward biased electroluminescence at room temperature although the efficiency of this emission is found to fall rapidly as the peak wavelength is increased toward 9 μm due to increased Auger recombination rates. By reverse biasing them, however, the devices show negative luminescence as a result of reducing the electron and hole densities below their thermal equilibrium value. The diode emitters have a higher quantum efficiency when used in this mode due to Auger suppression of the dark current.     

MWIR and LWIR HgCdTe Infrared Detectors Operated with Reduced Cooling Requirements

In this work, we analyze Auger suppression in HgCdTe alloy-based device structures and determine the operation temperature improvements expected when Auger suppression occurs. We identified critical material (absorber dopant concentration and minority-carrier lifetime) requirements that must be satisfied for optimal performance characteristics. Calculated detectivity values of Auger-suppressed and standard double-layer planar heterostructure (DLPH) devices demonstrate consistently higher maximum background-limited temperatures over a range of cutoff wavelengths and generally higher detectivity values achieved by Auger-suppressed detectors. Furthermore, these devices can operate with comparable performance at up to 100 K higher than DLPH detectors operating at reference temperatures above 100 K. Results of these simulations demonstrate that Auger-suppressed detectors provide a significant advantage over DLPH devices for high-temperature operation and are a viable candidate for thermoelectrically cooled detectors. Experimental dark current–voltage (I–V) characteristics between 120 K and 300 K were fitted using numerical simulations. By fitting the temperature-dependent I–V experimental data, we determined that the observed negative differential resistance (NDR) is due to Auger suppression. More specifically, NDR is attributed to full suppression of Auger-1 processes and partial (~70%) suppression of Auger-7 processes. After Auger suppression, the remaining leakage current is principally limited by the Shockley–Read–Hall recombination component. Part of the leakage current is also due to a residual Auger-7 current in the absorber due to the extrinsic p-type doping level. Analysis and comparison of our theoretical and experimental device results in structures where Auger suppression was realized are also presented.     

Noise in solid-state devices and lasers

A survey is given of the most important noise problems in solid-state devices. Section II discusses shot noise in metal-semiconductor diodes, p-n junctions, and transistors at low injection; noise due to recombination and generation in the junction space-charge region; high-level injection effects; noise in photodiodes, avalanche diodes, and diode particle detectors, and shot noise in the leakage currents in field-effect transistors (FETs). Section III discusses thermal noise and induced gate noise in FETs; generation-recombination noise in FETs and transistors at low temperatures; noise due to recombination centers in the space-charge region(s) of FETs, and noise in space-charge-limited solid-state diodes. Section IV attempts to give a unified account of 1/f noise in solid-state devices in terms of the fluctuating occupancy of traps in the surface oxide; discusses the kinetics of these traps; applies this to flicker noise in junction diodes, transistors, and FETs, and briefly discusses flicker noise in Gunn diodes and burst noise in junction diodes and transistors. Section V discusses shot noise in the light emission of luminescent diodes and lasers, and noise in optical heterodyning. Section VI discusses circuit applications. It deals with the noise figure of negative conductance amplifiers (tunnel diodes and parametric amplifiers), and of FET, transistor, and mixer circuits. In the latter discussion capacitive up-converters, and diode, FET, and transistor mixers are dealt with.     

二极管非制冷红外探测器及其读出电路设计

针对非制冷红外技术的低成本高性能应用,提出了基于SOI的二极管红外探测器及其读出电路的集成设计方案。阐述了二极管非制冷红外探测器的基本原理和工艺实现。对探测器的电学特性进行理论推导,得出读出电路的设计指标。采用连续时间自稳零电路结构实现探测器输出信号的低噪声低失调放大,采用级联滤波器以减弱开关非理想因素的影响,并采用片内电容采样保持,使得I/O引脚数较少,从而减小版图面积。采用spectre工具进行仿真,在CSMC 0.5 m 2P3M CMOS工艺下实现。结果表明:读出电路性能良好,闭环增益为65.8 dB,等效输入噪声谱密度为450 nV/Hz,等效输入失调电压100 V以内,功耗为5 mW,能实现探测器信号的准确读出。     

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．     

HgCdTe/CdTe/Si infrared photodetectors grown by MBE for near-room temperature operation

Conventional HgCdTe infrared detectors need significant cooling in order to reduce noise and leakage currents resulting from thermal generation and recombination processes. Although the need for cooling has long been thought to be fundamental and inevitable, it has been recently suggested that Auger recombination and generation rates can be reduced by using the phenomena of exclusion and extraction to produce nonequilibrium carrier distributions. The devices with Auger suppressed operation requires precise control over the composition, and donor and acceptor doping. The successful development of the molecular beam epitaxy (MBE) growth technique for multi-layer HgCdTe makes it possible to grow these device structures. Theoretical calculations suggest that the p n+ layer sequence is preferable for near-room temperature operation due to longer minority carrier lifetime in lightly doped p-HgCdTe absorber layers. However, because the low doping required for absorption and nonequilibrium operation is easier to achieve in n-type materials, and because Shockley-Read centers should be minimized in order to obtain the benefits of Auger suppression, we have focused on p⁺ n structures. Planar photodiodes were formed on CdTe/Si (211) composite substrates by As implantation followed by a three step annealing sequence. Three inch diameter Si substrates were employed since they are of high quality, low cost, and available in large areas. Due to this development, large area focal plane arrays (FPAs) operated at room temperature are possible in the near future. The structures were characterized by FTIR, x-ray diffraction, temperature dependent Hall measurements, minority carrier lifetimes by photoconductive decay, and in-situ ellipsometry. To study the relative influence of bulk and surface effects, devices with active areas from 1.6 10⁻⁵ cm² to 10⁻³ cm² were fabricated. The smaller area devices show better performance in terms of reverse bias characteristics indicating that the bulk quality could be further improved. At 80 K, the zero bias leakage current for a 40 m 40 m diode with 3.2 m cutoff wavelength is 1 pA, the R₀A product is 1.1 10⁴-cm² and the breakdown voltage is in excess of 500 mV. The device shows a responsivity of 1.3 10⁷ V/W and a 80 K detectivity of 1.9 10¹¹ cm-Hz^1/2/W. At 200 K, the zero bias leakage current is 5 nA and the R₀A product 2.03-cm², while the breakdown voltage decreases to 40 mV.     

Reliability and performance limitations in SiC power devices

Despite silicon carbide’s (SiC’s) high breakdown electric field, high thermal conductivity and wide bandgap, it faces certain reliability challenges when used to make conventional power device structures like power MOS-based devices, bipolar-mode diodes and thyristors, and Schottky contact-based devices operating at high temperatures. The performance and reliability issues unique to SiC discussed here include: (a) MOS channel conductance/gate dielectric reliability trade-off due to lower channel mobility as well as SiC–SiO₂ barrier lowering due to interface traps; (b) reduction in breakdown field and increased leakage current due to material defects; and (c) increased leakage current in SiC Schottky devices at high temperatures.Although a natural oxide is considered a significant advantage for realizing power MOSFETs and IGBTs in SiC, devices to date have suffered from poor inversion channel mobility. Furthermore, the high interface state density presently found in the SiC–SiO₂ system causes the barrier height between SiC and SiO₂ to be reduced, resulting in increased carrier injection in the oxide. A survey of alternative dielectrics shows that most suffer from an even smaller conduction band offset at the SiC–dielectric interface than the corresponding Silicon–dielectric interface and have a lower breakdown field strength than SiO₂. Thus, an attractive solution to reduce tunneling such as stacked dielectrics is required.In Schottky-based power devices, the reverse leakage currents are dominated by the Schottky barrier height, which is in the 0.7–1.2 eV range. Because the Schottky leakage current increases with temperature, the SiC Schottky devices have a reduction in performance at high temperature similar to that of Silcon PN junction-based devices, and they do not have the high temperature performance benefit associated with the wider bandgap of SiC.Defects in contemporary SiC wafers and epitaxial layers have also been shown to reduce critical breakdown electric field, result in higher leakage currents, and degrade the on-state performance of devices. These defects include micropipes, dislocations, grain boundaries and epitaxial defects. Optical observation of PN diodes undergoing on-state degradation shows a simultaneous formation of mobile and propagating crystal stacking faults. These faults nucleate at grain boundaries and permeate throughout the active area of the device, thus degrading device performance after extended operation.     

Cadmium sulfide passivation of InGaAs/InP mesa p-i-n photodiodes

A cadmium sulfide (CdS) passivation process was demonstrated for the first time on InGaAs/InP p-i-n mesa photodetectors. The passivated devices produced lower reverse bias leakage currents in comparison to devices that received only a thermally deposited SiO₂ film. The subsequent deposition of SiO₂ on the passivated devices produced virtually no change to the aforementioned leakage currents even after undergoing a 3-h, 300°C thermal treatment. In contrast, similar SiO₂ capped devices, fabricated without the CdS passivating layer, show a large increase in leakage current when subjected to the same thermal cycle. Leakage current versus mesa diameter measurements suggest these results are due to reduce surface recombination at the exposed mesa sidewall. X-ray photoelectron spectroscopy (XPS) results indicate the S:Cd ratio of these films to be 0.77.     

Hg1-xCdxTe长波光伏探测器的低频噪声研究

在同一Hg1-xCdxTe晶片上（x=0．217）制备了单层ZnS钝化和双层（CdTe＋ZnS）钝化的两种器件,对器件的低频噪声和暗电流进行了测试．发现单层钝化的器件在反偏较高时具有较高的低频噪声,在对器件的暗电流拟合计算中发现,单层钝化的器件具有较大的表面隧道电流,而这正是单层钝化器件具有较高低频噪声的原因．并通过高分辨X射线衍射中的倒易点阵技术RSM（reciprocal space mapping）研究了两种钝化对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的低频噪声和表面隧道电流的原因．     

非制冷红外探测器研究进展（特邀）

非制冷红外探测器由于无需制冷装置,能够工作在室温状态下,具有成本低、体积小、功耗低等特点,在红外领域得到了广泛的应用。在军事应用方面,非制冷型探测器的应用逐渐进入了之前制冷型探测器的应用范围,大量应用在一些低成本的武器系统,甚至在一些应用领域取代了原来的非制冷型探测器。在民用领域方面,更表现出了其价格和使用方便的优势,在民用车载夜视、安防监控等应用领域引起了广泛的兴趣和关注。文中介绍了Bolometer、热释电、热电堆等几种典型非制冷红外探测器的工作原理,列举了目前已实现商业化应用的主要产品在国内外的情况,着重介绍了目前应用最广泛的Bolometer器件主流产品的像元间距、阵列规格、性能及其封装发展的情况。除了已实现商业化应用的Bolometer、热释电、SOI二极管等探测器等产品,还详细介绍了一些非制冷探测新技术或新型器件:比如超表面在增强某些波段吸收方面的应用,新材料的Bolometer探测器、双材料新型非制冷器件、石墨烯、量子点、纳米线等光电探测技术的研究进展。最后文章还对今后非制冷红外探测器的发展趋势作了预测。     

大功率InGaAsP/GaAs量子阱半导体激光器的直流和1/f噪声性质

对大功率InGaAsP/GaAs量子阱(QW)半导体激光器(LD)的直流(DC)特性和小注入下的低频噪声(LFN)特性进行了实验研究.DC检测发现,V-J和I dV/dI-I可以对LD的电流泄漏作出判断.LFN检测发现,小注入下的1/f低频电压噪声幅值Bv(I)∝I<'βv>.理论分析和老化实验均表明,电流指数βv与载流子输运和电流泄漏机制之间有很好的相关性,存在电流泄漏和无辐射复合的器件其|βv|较小,可靠性较差.     

Investigations into the source of 1/f noise in Hg<Subscript>x</Subscript>Cd<Subscript>1−x</Subscript>Te diodes

This work is aimed at elucidating the mechanism of 1/f noise in Hg_xCd_1−xTe diodes in order to reduce 1/f noise in high-performance thermal cameras. Currently, to reach the required signal-to-noise ratio, the operating temperature of thermal cameras is 77 K. If 1/f noise could be reduced, this operating temperature could be raised without reducing the signal-to-noise ratio, allowing cheaper, smaller, and lighter cooling systems to be used. There are still some fundamental aspects of 1/f noise that are not fully understood. One aspect in particular is whether the noise is caused by mobility or number density fluctuations because both could give the conductivity fluctuations observed. This paper explores the noise coupling and current coupling between diodes on an array. It is shown that 1/f noise is present on the photons emitted from a forward-biased diode, suggesting that the rate of radiative recombination fluctuates. The results suggest that these fluctuations are due to carrier number-density fluctuations. From correlation measurements, it is shown that at least 32% of the 1/f noise in the forward-biased diode is correlated with carrier density fluctuations in Hg_xCd_1−xTe diodes.     

p-n junction—Schottky barrier hybrid diode

A new fabrication technique for passivated silicon Schottky barrier diodes is described. It is shown that the p-n junction guard ring or "hybrid" approach produces Schottky barriers whose forward and reverse electrical characteristics are in excellent agreement with simple theory, and that the excess noise normally found in passivated Schottky barrier diodes has been significantly reduced. The influence of metal barrier height and diffusion profile on the charge storage characteristics of these devices is discussed and examined experimentally.     

Nanoscale Engineering for Reducing Phase Noise in Electronic Devices

An investigation of electronic 1/f noise in ultrasmall devices and systems is presented, focused on nanoscale engineering of electronic devices for low phase noise. The investigation is based on the quantum 1/f formulas. Nanotechnology raises new questions of electronic noise, since fluctuations are more important in smaller devices. Based on the quantum 1/f noise theory, we find that in a certain transition range of sizes this general law is suspended, but reappears for 1/f noise in the nanometer domain, where the transition from coherent to conventional quantum 1/f effect is complete. The coherent and conventional quantum 1/f effects and their connection are briefly derived. The resulting quantum 1/f formulas are used to derive the 1/f noise of GaN/AlGaN MODFETs, resonant tunneling diodes, bulk acoustic wave and surface acoustic wave quartz resonators, microelectromechanical systems resonators,and spin valves. They are also used to calculate phase noise in these devices and in oscillators based on them, from first principles along with some classical noise sources. Device optimization is thus facilitated for ultrasmall devices.     

论高工作温度碲镉汞红外探测器（下）

与用其他材料制备的红外光子探测器相比,碲镉汞红外探测器具有带隙灵活可调、量子效率较高以及R_oA接近理论值等优点。碲镉汞探测器的主要缺点是需要低温制冷,以抑制引起噪声的热生自由载流子。期望碲镉汞探测器在具有高工作温度(High Opeating Temperature,HOT)的同时而又无需牺牲性能。HOT碲镉汞探测器的设计目标主要是抑制俄歇过程,从而降低探测器噪声和低温制冷需求。从相关基本概念出发,讨论了对HOT碲镉汞物理机制的理解以及近年来HOT碲镉汞技术的发展状况。     

论高工作温度碲镉汞红外探测器（上）

与用其他材料制备的红外光子探测器相比,碲镉汞红外探测器具有带隙灵活可调、量子效率较高以及R_0A接近理论值等优点。碲镉汞探测器的主要缺点是需要低温制冷,以抑制引起噪声的热生自由载流子。期望碲镉汞探测器在具有高工作温度(High Operating Temperature,HOT)的同时而又无需牺牲性能。HOT碲镉汞探测器的设计目标主要是抑制俄歇过程,从而降低探测器噪声和低温制冷需求。从相关基本概念出发,讨论了对HOT碲镉汞物理机制的理解以及近年来HOT碲镉汞技术的发展状况。     

Effect of reactive ion etch-induced damage on the performance of 4H-SiC schottky barrier diodes

The effect of reactive ion etch (RIE) induced damage on 4H-SiC surfaces etched in fluorinated plamas has been investigated and characterized using Ni Schottky diodes and x-ray photoelectron spectroscopic surface analysis. The diodes were characterized using current-voltage, current-voltage-temperature, and capacitance-voltage measurements with near ideal forward characteristics (n=1.07) and forward current density as high as 9000 A/cm² from the control (unetched) devices. High current handling capability was observed in diodes with etched surfaces as well. Diodes with surfaces etched in CHF₃ containing plasmas showed a significant reduction in the barrier height compared to the diodes with surfaces etched in CF₄ containing plasma. Control devices exhibited high leakages when reverse biased, which is attributed to the presence of a thin (∼2 nm) oxide layer at the metal-semiconductor interface. However, under reverse bias diodes with CHF₃-etched surfaces showed improvement in leakage current compared to diodes with CF₄-etched surfaces and the control diodes.