甚长波量子阱红外探测器的暗电流特性研究

基于载流子在量子结构中的输运理论研究了甚长波量子阱红外探测器(峰值响应波长15μm，量子阱个数大于40)的载流子的输运性质.研究结果表明，在甚长波量子阱红外探测器中，电流密度一般很低，暗电流主要来源于能量高于势垒边的热激发电子.通过薛定谔方程和泊松方程以及电流的连续性方程的自洽求解，发现外加偏压下电子浓度在甚长波器件各量子阱的分布发生较大变化，电场在整个器件结构上呈非均匀分布，靠近发射极层的势垒承担的电压远远高于均匀分布的情形.平带模型假定电压在器件体系上均匀分布，导致小偏压下的理论计算值远远低于实验值. 关键词： 甚长波量子阱红外探测器 量子波输运 暗电流     

Comparative study between different quantum infrared photodetectors

This paper presents a theoretical analysis for the dark current characteristics of different quantum infrared photodetectors. These quantum photodetectors are quantum dot infrared photodetectors (QDIP), quantum wire infrared photodetectors (QRIP), and quantum well infrared photodetectors (QWIP). Mathematical models describing these devices are introduced. The developed models accounts for the self-consistent potential distribution. These models are taking the effect of donor charges on the spatial distribution of the electric potential in the active region. The developed model is used to investigate the behavior of dark current with different values of performance parameters such as applied voltage, number of quantum wire (QR) layers, QD layers, lateral characteristic size, doping quantum wire density and temperature. It explains strong sensitivity of dark current to the density of QDs/QRs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among them are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors.     

Non-Gaussian noise in quantum wells infrared photodetectors

Non-Gaussian dark current noise has been observed in quantum wells infrared photo detectors. The non-Gaussian component of the noise was ascribed to fluctuations of spatial distribution of electric field in the device. Non-Gaussian noise was found in both n- and p-type QWIPs, however, it was significantly less pronounce. In n-type devices non-Gaussian noise manifests itself only as randomly distributed excess current bursts. In p-type QWIPs the non-Gaussian noise takes form of bias dependent random telegraph-like fluctuations with a finite time of transition between the levels. The lifetime at both levels is Poisson distributed and the average lifetime, together with the level spacing, strongly depend on bias voltage. At low voltages the system stays predominantly in the low current level while at higher voltages the average lifetime of the high current level is longer. The transient time of passing between the states has been related to the charging time constant of the system determined by QWIP capacitance and contacts resistance.     

Numerical analysis of SiGeSn/GeSn interband quantum well infrared photodetector

In this paper, detailed theoretical investigation on the frequency response and responsivity of a strain balanced SiGeSn/GeSn quantum well infrared photodetector (QWIP) is made. Rate equation and continuity equation in the well are solved simultaneously to obtain photo generated current. Quantum mechanical carrier transport like carrier capture in QW, escape of carrier from the well due to thermionic emission and tunneling are considered in this calculation. Impact of Sn composition in the GeSn well on the frequency response, bandwidth and responsivity are studied. Results show that Sn concentration in the GeSn active layer and applied bias have important role on the performance of the device. Significant bandwidth is obtained at low reverse bias voltage, e.g., 200?GHz is obtained at 0.28?V bias for a single Ge_0.83Sn_0.17 layer. Whereas, the maximum responsivity is of 8.6?mA/W at 0.5?V bias for the same structure. However, this can be enhanced by using MQW structure.     

The role of sequential tunnelling in the dark current of quantum well infrared photodetectors (QWIPs)

A quantum mechanical approach is taken to investigate the contribution of sequential tunnelling as a component of the dark current in quantum well infrared photodetectors (QWIPs). Calculations are performed on three different experimentally reported QWIP devices made for different detection wavelengths. The results show that the sequential tunnelling component remains rather constant with different devices, however it is swamped by the thermionic emission components of the dark current at longer wavelengths. The lack of a local maximum in the dark current due to resonant LO phonon emission, which should be observed at short wavelengths, suggests that interface roughness and alloy disorder could be destroying the coherence of the electron wavefunctions between quantum wells.     

A “capacitor” model of the hysteresis of tunneling current in w -GaN/AlGaN(0001) structures

A “capacitor” model of the hysteresis is developed using the self-consistent calculation of the tunneling current in a w-GaN/AlGaN(0001) double-barrier structure. In the framework of this model, the current jumps and changes in the potential and the electric field in the structure upon transition from one branch of the current loop to the other branch are considered a result of the recharging of two joined capacitors with the plates located at the positions of the extrema of variations in the electron density in the regions of the emitter, the quantum well, and the collector. It is demonstrated that, when the external and internal fields in the quantum well compensate for each other, the tunneling current is sharply and irreducibly switched to the characteristics of the other resonance and forms a wide hysteresis loop so that, in the branches of this loop, the charge is redistributed between the quantum well and the collector. If the fields coincide with each other, there arises a narrow “singleresonance” hysteresis loop, which is accompanied by the transfer of the electron charge from the emitter to the collector. The developed model leads to agreement with the results of the self-consistent calculations and provides an illustrative interpretation of the complex electron tunneling processes. Original Russian Text ? A.N. Razzhuvalov, S.N. Grinyaev, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 1, pp. 168–177.     

The role of emitter quasi-bound state and scattering on intrinsic bistability in resonant tunneling diodes

Usually, numerical self-consistent calculations predict a much larger intrinsic bistability region than actually is measured in resonant tunneling diodes (RTDs). In addition, numerical calculations have shown that scattering in the well reduces bistability. We used a unified treatment of current flowing from continuum states and emitter quasi-bound states to show numerically and analytically that not only the scattering in the quantum well but also the scattering in the emitter reduces bistability. Moreover, within the Hartree approximation, bistability occurs by tunneling resonantly between emitter quasi-bound state and well quasi-bound state as a pitchfork bifurcation.     

Quantum transport in quantum well infrared photodetectors in the tunneling regime

Quantum well infrared photodetectors (QWIP) are good candidates for low photon flux detection in the 12–20 μm range. For particularly low incident power applications, it can be interesting to reduce the operating temperature to reach the ultimate performance of the QWIP (low dark current, low noise, high detectivity). Nevertheless, once the QWIP operates in the tunneling regime, the dark current is no longer improved by reducing the temperature. Thus, further improvement of the performance needs a microscopic understanding of the physical phenomena involved in QWIP operation in the tunneling regime. In this paper we focus on the dark current of QWIP operated at very low temperature (4–20 K). Experimental results obtained on a 14.5 μm peaking device revealed a plateau regime in the IV curves. We first modeled the dark current using the WKB approximation, but it failed to reproduce the shape and order of magnitude of the phenomenon. As an improvement, we developed a scattering formalism. Our model includes all the most common interactions observed in GaAs: optical phonon, acoustical phonon, alloy disorder, interface roughness, interaction with ionized impurities and between carriers. We demonstrate that, as far as the tunneling regime is concerned, the dominant interaction is the one between electron and ionized impurities, which allows us to conclude on the influence of the doping profile on the dark current.     

Photocurrent response in a double barrier structure with quantum dots–quantum well inserted in central well

We report the photocurrent response in a double barrier structure with quantum dots–quantum well inserted in central well. When this quantum dots–quantum well hybrid heterostructure is biased beyond +1 or −1 V, the photocurrent response manifests itself as a step-like enhancement, increasing linearly with the light intensity. Most probably, at proper bias condition, the pulling down of the X minimum of GaAs at the outgoing interface of the emitter barrier by the photovoltaic effect in GaAs QW will initiate the Γ–X–X tunneling at much lower bias as compared with that in the dark. That gives rise to the observed photocurrent response.     

15 μm Quantum Well Infrared Photodetector for thermometric imagery in cryogenic windtunnel

Quantum Well Infrared Photodetector (QWIP) usually suffer from a too moderate quantum efficiency and too large dark current which is often announced as crippling for low flux applications. Despite this reputation we demonstrate the ability of QWIP for the low infrared photon flux detection. We present the characterization of a state of the art 14.5 μm QWIP from Alcatel-Thales III–V Lab. We developed a predictive model of the performance of an infrared instrument for a given application. The considered scene is a cryogenic wind tunnel (ETW), where a specific Si:Ga camera is currently used. Using this simulation tool we demonstrate the QWIP ability to image a low temperature scene in this scenario. QWIP detector is able to operate at 30 K with a NETD as low as 130 mK. In comparison to the current detector, the operating temperature is 20 K higher. The use of a QWIP based camera would allow a huge simplification of the optical part.     

Gain and transient photoresponse of quantum well infrared photodetectors: a detailed ensemble Monte Carlo study

We investigate different gain characteristics observed on quantum well infrared photodetectors (QWIPs) fabricated with various material systems, and the effects of barrier material properties on the device characteristics through detailed ensemble Monte Carlo simulations. When the energy spacing between the central and satellite valleys is increased, the improvement in the excited electron lifetime is found to be much stronger than that in the average electron velocity in the device. According to our results, relatively high gain observed in InP/In_0.53Ga_0.47As QWIPs under large bias is not due to the higher mobility in InP as suggested earlier; it can mainly be attributed to higher excited electron lifetime as a result of relatively large Γ–L energy spacing. We discuss the details of the fast part of the Al_0.3Ga_0.7As/GaAs QWIP transient photoresponse, which exhibits three regions with different decay characteristics under a short pulse of radiation. The duration of the final region, during which the electrons excited near the emitter are extracted from the collector, is observed to be considerably long due to the dispersion of the photoelectrons. The photoresponse time rapidly decreases with increasing bias under low bias, and nearly saturates at 10 ps under large bias being 40% larger than the average transit time estimated by dividing the device length to the average steady-state electron velocity in device. We also investigate the effects of the interface reflections on the photoresponse time.     

Magneto-tunneling spectroscopy of GaAs---AlGaAs double barrier tunneling devices in pulsed high magnetic fields up to 40T

The magneto-tunneling effect was investigated in GaAs---AlGaAs double barrier resonant tunneling devices in pulsed high magnetic fiels up to 40T applied parallel(B) and perpendicular (B) to the barrier layers. In a sample with , oscillatory structures due to the 2D electrons in the emitter and the LO phonon assisted resonant tunneling were observed when the magnetic field (B) was swept at constant bias voltages. A large drop of the current was found in the quantum limit at applied voltages below the negative differential conductivity region. A striking hysteresis was observed in the voltage-current (V - I) curves. In a wide well sample with , rich structures were observed in the V - I curve for B, corresponding to the tunneling to different cyclotron orbits from the emitter.     

A study of the dark currents of InSb charge injection devices

The dark currents of InSb metal-insulator-semiconductor (MIS) charge injection devices (CIDs) in the temperature range 30 to 120K are studied. It is found that a thermal-generating process dominates the dark current in the high temperature region. When the device is under small bias voltage, a bump in the trap emission current appears below 70K. This current is due to carrier capture and emission processes of a hole trap state located in the bulk material, and the measured activation energy is 50meV. For larger bias conditions, the band-to-band tunnelling current gradually overcomes the trap emission current. It smears out the bump in the trap emission current, and shows a slightly temperature-dependent behaviour in the plot. The effects of field electrodes are also studied. It is found from experimental results that the edge of the electric field around the device periphery plays an important role in the band-to-band tunnelling process, and a field electrode with suitable bias can improve the dark current response drastically.     

Carrier transport effects on the photocurrent spectra of an intrinsic GaAs/AlGaAs multiple quantum well with highly doped AlGaAs contact layers

In this study, we demonstrate how electroreflectance (ER) measurements as a function of bias, and of angle of incidence (θ₀), together with bias dependent photocurrent (PC) measurements, can be used to provide understanding of the complex electric field profile and carrier transport effects in a GaAs/Al_0.3Ga_0.7As multiple quantum well (MQW), grown inside n⁺ contact layers. The PC measurements exhibit split excitonic features, the components of which change in strength with the applied bias. The effect is explained by absorption in the front of the MQW stack, with the back of the stack acting as detector. We examine the θ₀-dependence of the ER lineshape, to determine the depth of the layers responsible for each feature. The ER and PC lineshapes and their bias dependence are explained by the unusual electric field profile across the stack. The field profile appears to be determined by tunnelling of the dark current.     

空穴在动量空间分布对p型量子阱红外探测器响应光谱的影响

通过对p型量子阱红外探测器(QWIP)的自洽计算，得到了量子阱价带的电子结构和器件的光电流谱，并研究了载流子在动量空间分布对p型QWIP光谱响应的影响.计算结果表明，在动量空间不同区域的空穴对器件的光谱响应起着不同作用，从而使得在p型QWIP中，空穴浓度和温度都将影响器件的响应光谱.所得结果合理地解释了实验中器件响应光谱随掺杂浓度和温度的变化. 关键词： p型量子阱红外探测器 响应光谱 空穴浓度 温度     

Photoconductive spectral analysis of InAs quantum dot under normal incidence

InAs/InAlAs-on-InP quantum dots were implemented for infrared photodetection. The photoconductive spectra were measured as a function of polarization angle and bias. Normal incidence configuration was employed, to emphasize the contrast to the response in quantum well infrared photodetectors (QWIPs). Several peaks were observed, ranging from 90 to 420 meV. The strongest peak, at around 95 meV, is highly polarized. The superlinear increase of the intensity with bias, due to bound-to-bound transition followed by tunneling, was modeled successfully by WKB approximation. I–V characteristics show no improvement over QWIP performance.     

Dynamics of resonant and non-resonant tunneling in asymmetric coupled quantum wells

Within the framework of the effective mass approximation, coherent oscillations of a photoexcited electron wave packet in an asymmetric coupled quantum well structure have been studied using a time-dependent Schrödinger equation. In the method of calculation, the continuity of the current across a semiconductor heterojunction is considered. The amplitude and period of the electronic is obtained and in the case of high bias, it is found the existence of electric field-induced tunelling to semiconductor bulk.     

Modelling of high-temperature dark current in multi-quantum well structures from MWIR to VLWIR

In this paper, a model to calculate the dark current of quantum well infrared photodetectors at high-temperature regime is presented. The model is derived from a positive-definite quantum probability-flux and considers thermionic emission and thermally-assisted tunnelling as mechanisms of dark current generation. Its main input data are the wave functions obtained by time-independent Schrodinger equation and it does not require empirical parameters related to the transport of carriers. By means of this model, the dark current of quantum well infrared photodetectors at high-temperature regime is investigated with respect to the temperature, the barrier width, the applied electric field and the position of the first excited state. The theoretical results are compared with experimental data obtained from lattice-matched InAlAs/InGaAs, InGaAsP/InP on InP substrate and AlGaAs/GaAs structures with rectangular wells and symmetric barriers, whose absorption peak wavelengths range from MWIR to VLWIR. The corresponding results are in a good agreement with experimental data at different temperatures and at a wide range of applied electric field.