Carrier scattering approach to the origins of dark current in mid and far-infrared (terahertz) quantum-well intersubband photodetectors(QWLPs)

A carrier scattering approach is taken in an analysis of the affect on the dark current of extending the operating wavelength of conventional bound to continuum quantum-well intersubband photodetectors. It is found that both the sequential tunneling and the thermionic emission contributions to the dark current increase as the wavelength of the detector is extended from the mid- to far-infrared. Dark current designs rules are derived     

Photoresponse study of normal incidence detection in p-type GaAs/AIGaAs multiple quantum wells

We studied p-type GaAs/AIGaAs multiple quantum well (MQW) materials as a possible alternative to the current n-type GaAs/AIGaAs MQWs for infrared detection. The advantage of p-type MQWs is that absorption of infrared radiation at normal incidence is not selection rule forbidden as it is for the n-type. We have verified that significant photoresponse occurs at normal incidence in p-type MQWs. We studied changes in the photoresponse spectrum as a function of well width and temperature. The MQW heterostructures were designed to use bound to continuum intersubband absorption in the GaAs valence band and to have a peak photoresponse near 8 μm. The photoresponse spectrum was compared to the first theoretical model of the bound to continuum absorption in p-type GaAs/ AlGaAs MQWs. The theoretical absorption curve was found to be in good qualitative agreement with the experimental results.     

级联倍增InAlAs/InAlGaAs雪崩光电二极管暗电流成分分析

实验制备了级联倍增InAlAs/InAlGaAs雪崩光电二极管,对二极管暗电流随台面直径和温度的变化进行了研究分析。结合暗电流函数模型,利用Matlab软件对暗电流的各成分进行了数值计算,并仿真研究了芯片结构的缺陷浓度Nt和表面复合速率S对暗电流的影响。结果表明,二极管暗电流主要来自于体暗电流,而非表面漏电流。在工作点偏压90V处,受缺陷影响的缺陷辅助隧穿电流Itat在暗电流中占据了主导,并推算出了芯片结构的缺陷浓度Nt约为1019 m-3、吸收区中的缺陷浓度NInGaAs约为7×1015 m-3。由于芯片结构的缺陷主要来源于InAlAs/InAlGaAs倍增区和InGaAs吸收区,而吸收区缺陷占比很少,因此认为缺陷主要来自于异质结InAlAs/InAlGaAs倍增区。     

Analysis of dark current in IR detectors on thinned p-type HgCdTe

A model for the diffusion dark current in MIS IR detectors on thinned bulk p-type HgCdTe is discussed. The model includes trap-assisted tunneling mechanisms in the back-side depletion region as well as the effects of fast surface states. Expressions for the net recombination rate are developed for situations in which trap-assisted tunneling transitions are allowed. Calculations for 12-μm optical cutoff detectors operating at liquid-nitrogen temperature show that the properties of the back side, including surface fixed charge density, depletion region trap density, fast surface-state density, and majority carrier concentration, have a strong influence on the dark current levels of detectors on thin material. It is predicted that typical as-fabricated surface parameters will not result in large dark current densities. Calculations for detectors with surface parameters common to stressed (degraded) back surfaces, however, show dark current densities which would significantly affect detector performance     

4H-SiC紫外光电探测器光电特性随温度变化的研究

利用光电流谱法研究了300K到60K温度范围内的p-i-n结构4H-SiC紫外光电探测器的暗电流及相对光谱响应特性。研究发现随着温度的降低,探测器的暗电流和相对光谱响应都逐渐减小;而且,反向偏压越高,暗电流减小的速率越大。在零偏压下,随着温度的降低,器件的温度从300K降低到60K时,相对光谱响应的峰值波长先向短波方向移动,后向长波方向移动,在60K时移至从272nm附近移至282nm附近;同时观察到探测器的相对光谱响应范围略有缩小,。此外,我们对器件并讨论了温度变化对器件p、i、n各层产生的光电流随温度变化的机理进行讨论,提出了可以通过减少i层缺陷和适当减小n层的掺杂浓度的方式来提高器件的相对光谱响应。     

Reliability of InGaAs/InP long-wavelength p-i-n photodiodes passivated with polyimide thin film

The long-term reliability of InGaAs/InP p-i-n photodiodes passivated with polyimide thin film was studied through a room temperature life test and through thermally accelerated life tests. No degradation in dark current was observed in a room temperature life test at a reverse bias of -15 V after aging for 7000 h. However, the dark current increased gradually in the accelerated life tests at 110°C, 130°C, and 150°C. It was confirmed that the activation energy of degradation in dark current was 0.85 eV and the average lifetime was estimated to be 10⁷h at room temperature. The dark current recovered in high temperature storage tests. The phenomenon of degradation and recovery was qualitatively explained by a model of accumulation and diffusion of mobile ions at a junction perimeter.     

MPP CCD扩散暗电流温度特性分析

研究了MPP CCD扩散暗电流的温度特性,分析了扩散暗电流在不同温度下对器件总暗电流的贡献和不同处理方式对评估器件高温暗电流的影响,并对此进行了实验验证。结果表明,扩散暗电流在高温下对器件总暗电流的影响很大,占据支配地位,是器件高温暗电流的主要来源。提出了两种优化方法,以降低扩散暗电流对器件高温暗电流的影响,提高MPP CCD的高温环境工作能力。     

MPP CCD暗电流温度特性研究

研究了MPP电荷耦合器件(CCD)暗电流和暗电流非均匀性的温度特性,并与非MPP CCD的暗电流和暗电流非均匀性的温度特性进行了对比分析。研究结果表明,MPP CCD抑制了表面暗电流,相较于非MPP CCD具有较低的暗电流和暗电流非均匀性,可以承受更高的工作温度。     

Very low dark current heterojunction CCD's

A model has been formulated which accounts for the major sources of dark current (JD) associated with a single pixel of a heterojunction, Schottky gate charge-coupled device (CCD). This model predicts the temperature dependence of JDand shows that for properly fabricated gates, bulk generation in the channel is the primary source of dark current. To verify the model, the dark current of Al0.3Ga0.7As/ GaAs n-p⁺heterostructure CCD's was measured over the temperature range 23-55°C. At room temperature,J_{D} approx 83pA/cm², typically, and some pixels have JDas low as 43 pA/cm². These are the lowest dark currents reported to date for a CCD structure. The data at 55°C show that, typically, JDincreases to ∼ 1 nA/cm². Furthermore, the data confirm the temperature dependence of JDpredicted by the model.     

新型GaAs/AlGaAs量子阱红外探测器暗电流特性

对基于GaAs/AlGaAs系子带间吸收的一种新型量子阱红外探测器,采用Poisson方程和Schrodinger方程,计算了新器件结构的能带结构、电子分布特性,在此基础上采用热离子发射、热辅助遂穿模型对器件的暗电流特性进行了模拟,计算结果与器件实测的暗电流特性吻合得很好,说明热离子发射、热辅助遂穿机制是形成器件暗电流的主要构成机制,增加垒高、降低阱中掺杂浓度及降低工作温度是抑制器件暗电流的主要途径,计算结果对进一步优化器件的设计将起到重要的理论指导作用．     

暗电流对短波红外偏振测量精度的影响

探测器暗电流及其测量不确定度是影响短波红外偏振测量仪器测量精度的最重要因素。首先,结合红外探测器的工作原理,分析并建立了暗电流影响下的红外探测系统噪声模型。根据分析结果设计实验获得短波红外探测器G5853-21暗电流与温度和反向偏压关系。然后,以分孔径偏振探测系统为例,推导了斯托克斯参数误差模型和偏振度误差模型。最后,重点分析空间环境应用背景下,针对暗电流影响的改进措施,提出了探测器精确温控的暗电流影响改进方案,并给出了短波红外探测器工作温度指标要求。结果表明:通过对探测器进行精确的温度控制以降低暗电流数值,可以将包含暗电流测量不确定度和其他噪声引起的偏振度测量误差控制在0.42%(=0.3时)以内。     

CCD表面暗电流特性研究

针对电荷耦合器件表面暗电流的温度特性和辐照特性进行了研究。研究结果表明,在不同温度下,表面暗电流不仅是CCD总暗电流的主要来源,且是CCD暗电流非均匀性的主要影响因素;CCD栅介质的硅-二氧化硅界面态密度随辐照剂量的增加而增加,导致CCD表面暗电流显著增加,是CCD经辐照后暗电流变大的主要影响因素。     

Low Dark Count Rate and High Single-Photon Detection Efficiency Avalanche Photodiode in Geiger-Mode Operation

An In_0.53Ga_0.47As-InP avalanche photodiode with very low dark current (0.15 pA at 95% breakdown voltage, 200 K) has been characterized in gated mode for single-photon detection. The temperature dependence of dark current and dark count yields activation energy of ~0.4 eV from 240 K to 297 K. High single-photon detection efficiency (SPDE) at telecom wavelengths with very low dark count rate (DCR) (e.g., DCR =12 kHz at SPDE =45% at 1.31 mum and 200 K) was achieved     

Forward and reverse current–voltage–temperature characteristics of a typical BPW34 photodiode

The dark forward and reverse current–voltage characteristics of a typical BPW34 silicon photodiode have been investigated in the temperature range 80–300 K. We propose that tunnelling enhanced recombination at or close to the p/i interface plays a significant role in the dark forward current. We show that Bardeen’s model for a modified Schottky-like interfacial junction can be satisfactorily applied to describe the reverse current–voltage characteristics at intermediate bias voltages.     

Current–voltage characteristics of organic heterostructure devices with insulating spacer layers

The dark current density in donor/acceptor organic planar heterostructure devices at a given forward voltage bias can either increase or decrease when an insulating spacer layer is added between the donor and acceptor layers. The dominant current flow process in these systems involves the formation and subsequent recombination of interfacial exciplex states. If the exciplex recombination rate limits current flow, an insulating interface layer decreases the dark current. However, if the exciplex formation rate limits the current, an insulating interface layer may increase the dark current. We present a device model to describe this behavior, and we discuss relevant experimental data.     

Refined model for the current-voltage characteristics of quantum-well infrared photodetectors

The temperature dependences of the dark current of quantum-well infrared photodetectors are investigated experimentally. It is established that the pre-exponential factor in the analytical expression for the photodetector current-voltage characteristics varies linearly with temperature. On the basis of the results obtained, it is suggested that the temperature dependence of the photodetector??s dark current is determined by the thermal excitation of charge carriers to a band characterized by a two-dimensional density of states. In the context of this suggestion, a refined model for the current-voltage characteristics is proposed. The model takes into account the thermal generation of charge carriers in a band with a two-dimensional density of states and the electric field dependence of the thermal activation energy for the quantum-well ground state and of the drift velocity of the carriers in the barrier conduction band.     

一种改进型金属-半导体-金属光电探测器数学模型

以E.Sano的金属-半导体-金属光电探测器(MSM-PD)模型为基础,提出了一种改进型的模型.该模型以多个电流源和电容并联的形式构造,以吸收区过剩电子和空穴总数为研究对象,求解速率方程.另外计算了电容,给出了暗电流与端电压的非线性计算式,改进了传统模型中暗电流的线性计算方法.通过线性叠加给出了该模型光电流的数学解析解.通过在Matlab中的模拟计算,表明该模型具有计算量小、准确度高的特点,它不仅能反映一定偏压和光照下光电流的变化,而且能展示光电子在器件中的转化过程.这种模型也能较好地应用于微弱信号的检测模拟.     

1/f noise and specific detectivity of HgCdTe photodiodes passivatedwith ZnS-CdS films

1/f noise in HgCdTe photodiodes has been measured as a function of temperature, diode bias, and dark current. The dependence of 1/f noise on dark current was measured over a wide temperature range. At low temperatures, where surface generation and leakage current were predominant, a linear relationship between 1/f noise and dark current was observed. At higher temperatures, where diffusion current is predominant, the correlation no longer holds. The temperature dependence of 1/f noise was also determined. The temperature dependence of the 1/f noise was found to be the same as that for the surface generation and leakage currents. All the data obtained in these experiments could be fit with theoretical predictions by a simple relationship between 1/f noise and dark current. The 1/f noise in the HgCdTe photodiode varies with diode bias, temperature, and dark current only through the dependence of the surface current on these devices. The maximum specific detectivity (D*) value and the maximum signal-to noise ratio are approximately 3.51×10¹⁰ cm·Hz^1/2/W and 5096 at 50 mV reverse bias, respectively     

Study of reverse dark current in 4H-SiC avalanche photodiodes

Temperature-dependent current-voltage (I-V) measurements have been used to determine the reverse dark current mechanisms in 4H-SiC avalanche photodiodes (APDs). A pn junction vertical mesa structure, passivated with SiO/sub 2/ grown by plasma enhanced chemical vapor deposition, exhibits predominate leakage current along the mesa sidewall. Similar APDs, passivated by thermal oxide, exhibit lower dark current before breakdown; however, when the temperature is higher than 146/spl deg/C, an anomalous dark current, which increases rapidly with temperature, is observed. This current component appears to be eliminated by the removal of the thermal oxide. Near breakdown, tunneling is the dominant dark current mechanism for these pn devices. APDs fabricated from a pp/sup -/n structure show reduced tunneling current. At room temperature, the dark current at 95% of breakdown voltage is 140 fA (1.8 nA/cm/sup 2/) for a 100-/spl mu/m diameter APD. At a gain of 1000, the dark current is 35 pA (0.44 /spl mu/A/cm/sup 2/).     

Zero-rate reliability of the exponential-server timing channel

We determine the reliability function of the exponential-server timing channel (ESTC) in the limit as the data rate approaches zero. The limit shows that at low rates, the ESTC is strictly more reliable than the Poisson channel without dark current, answering a question Arikan posed in these Transactions. The proof employs a distance metric over inputs to timing channels that parallels Euclidean and Hamming distance for conventional channels. A consequence of the proof is that bounded-distance decoding, with distance measured according to this metric, is exponentially optimum for the ESTC in the low-rate regime. We also prove the straight-line bound for the channel and a bound on the reliability of timing channels with general service distributions in the limit as the data rate approaches zero.