超长波GaAs/AlGaAs量子阱红外探测器光电流谱特性研究

研究了响应波长在15μm附近的超长波GaAs/AlGaAs量子阱红外探测器在不同外加偏压下的光电流谱特性.光电流谱上的两个主要由于阱宽随机涨落而呈现为高斯线形的响应峰被分别指认为量子阱基态E0到第一激发态E1和第三激发态E3的跃迁.跃迁峰随着器件上外加偏压的增大而出现线性红移现象，认为这种变化起源于激发态与基态对量子阱结构中势变化敏感性的不同，采用传输矩阵方法并考虑到电子交互作用修正进行的理论计算在定量上解释了实验结果. 关键词： 量子阱红外探测器 超长波 光电流 传输矩阵     

10—14 μm同时响应的双色量子阱红外探测器

实现截止波长为11.8和14.5 μm双色同时响应的量子阱红外探测器,可以同时工作在8—12 μm大气窗口和甚长波波段.在77 K下测量到很强的光电流谱.器件结构采取了较为简洁的设计,通过适当增大量子阱结构中势阱的宽度和选择合适的掺杂浓度,在同一偏压下实现了对两个波长的同时响应.两个光响应峰分别为基态到第五激发态和基态到第一激发态的跃迁吸收. 关键词： 量子阱红外探测器 双色 同时响应     

InAs/GaSb量子阱的能带结构及光吸收

采用八能带K-P理论以及有限差分方法,研究了沿[001]方向生长的InAs/GaSb二类断带量子阱体系的能带结构、波函数分布和对[110]方向线性偏振光的吸收特性.研究发现,通过改变InAs或GaSb层的厚度,可有效调节该量子阱体系的能带结构及波函数分布.计算结果表明,当InAs/GaSb量子阱的导带底与价带顶处于共振状态时,导带基态与轻空穴基态杂化效应很小,且导带基态与第一激发态的波函数存在较大的重叠,导带基态与第一激发态之间在布里渊区中心处的跃迁概率明显大于导带底与价带顶处于非共振状态时的跃迁概率.研究结果对基于InAs/GaSb二类断带量子阱体系的中远红外波段的新型级联激光器、探测器等光电器件的设计具有重要意义.     

插入生长AlGaAs薄膜对InAs量子点探测器性能的影响

利用分子束外延生长获得的两个InAs量子点样品制备了n型的量子点红外探测器.对于其中一个器件,在InAs量子点有源区的底部和顶部分别插入生长了AlGaAs势垒层.利用透射电阻显微技术研究了两个样品的结构特性;利用光致发光光谱和光电流谱研究了两个器件的光电性质.实验结果表明,AlGaAs层的插入对器件的探测性质有显著的影响.利用有三维效质量近似模型的计算结果,指认了带内光电流谱中峰结构的起源. 关键词： InAs 量子点 AlGaAs薄膜 光致发光光谱 有效质量近似模型     

具有新型有源区的量子级联探测器(特邀)

量子级联探测器是一种光伏型的子带间跃迁红外探测器,通过厚度渐变的啁啾量子阱中台阶状的子带分布,产生内建电场,使得有源区中的光生载流子定向输运,器件工作时无需外加偏压,避免了暗电流噪声的产生,能够实现室温长波红外响应。由于子带间跃迁吸收系数小、具有偏振选择性,量子级联探测器目前存在响应率低、对正入射响应无响应、探测率对温度敏感等问题。针对这些问题,本文介绍三种新型量子级联探测器有源区的设计,包括量子点/阱耦合、束缚-微带斜跃迁和小能量台阶有源区,在中波、长波和甚长波波段展现出优良的器件性能。     

共振声子太赫兹量子级联激光器研究

本文综述了共振声子太赫兹(THz)量子级联激光器(QCL)载流子输运及其光电特性的研究结果。我们采用Monte Carlo方法模拟了不同有源区结构的共振声子THz QCL,如四阱有源区和三阱有源区结构等,优化了THz QCL的器件参数。计算表明,器件的增益依赖于注入势垒的宽度、掺杂浓度和声子抽运能级间隔等参数。单阱注入的THz QCL可以获得低的激射频率,而三阱有源区结构的THz QCL具有更高的工作温度。我们数值模拟了这两种器件结构在不同寄生电压下的电子输运、增益以及温度特性等。同时,我们实验测量了THz QCL的发射谱偏压和温度效应,计算结果与实验相吻合。研究结果表明,随着偏压增加发射谱出现了明显的频率蓝移,多模激射仅出现在大电流注入情形。与偏压的密切依赖关系不同,激射频率对温度的变化并不敏感。     

插入生长AlGaAs薄膜对InAs量子点探测器性能的影响

利用分子束外延生长获得的两个InAs量子点样品制备了n型的量子点红外探测器.对于其中一个器件，在InAs量子点有源区的底部和顶部分别插入生长了AlGaAs势垒层.利用透射电阻显微技术研究了两个样品的结构特性；利用光致发光光谱和光电流谱研究了两个器件的光电性质.实验结果表明，AlGaAs层的插入对器件的探测性质有显著的影响.利用有三维效质量近似模型的计算结果，指认了带内光电流谱中峰结构的起源.     

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     

亚单层InGaAs量子点-量子阱异质结构的时间分辨光致发光谱

测定了亚单层InGaAs/GaAs量子点-量子阱异质结构在5K下的时间分辨光致发光谱.亚单层量 子点的辐射寿命在500 ps 至 800 ps之间，随量子点尺寸的增大而增大，与量子点中激子的 较小的横向限制能以及激子从小量子点向大量子点的隧穿转移有关.光致发光上升时间强烈 依赖于激发强度密度.在弱激发强度密度下，上升时间为 35 ps，纵光学声子发射为主要的 载流子俘获机理.在强激发强度密度下，上升时间随激发强度密度的增加而减小，俄歇过程 为主要的载流子俘获机理.该结果对理解亚单层量子点器件的工作特性非常有用. 关键词： 亚单层 量子点-量子阱 时间分辨光致发光谱     

直接带隙Ge耦合双量子阱中的光吸收系数

在有效质量近似下,详细研究了直接带隙Ge/Ge Si耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况.结果表明:随着量子阱阱宽增大,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象.增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升.此外,与非对称耦合量子阱相比,耦合效应对对称耦合量子阱中光吸收系数的影响更为显著.     

Quantum dot nanostructures for multi-band infrared detection

A dual-band (two-color) tunneling-quantum dot infrared photodetector (T-QDIP) structure, which provides wavelength selectivity using bias voltage polarity, is reported. In this T-QDIP, photoexcitation takes place in InGaAs QDs and the excited carriers tunnel through an AlGaAs/InGaAs/AlGaAs double-barrier by means of resonant tunneling when the bias voltage required to line up the QD excited state and the double-barrier state is applied. Two double-barriers incorporated on the top and bottom sides of the QDs provide tunneling conditions for the second and the first excited state in the QDs (one double-barrier for each QD excited state) under forward and reverse bias, respectively. This field dependent tunneling for excited carriers in the T-QDIP is the basis for the operating wavelength selection. Experimental results showed that the T-QDIP exhibits three response peaks at ～4.5 (or 4.9), 9.5, and 16.9 μm and selection of either the 9.5 or the 16.9 μm peak is obtained by the bias polarity. The peak detectivity (at 9.5 and 16.9 μm) of this detector is in the range of 1.0–6.0 × 10¹² Jones at 50 K. This detector does not provide a zero spectral crosstalk due to the peak at 4.5 μm not being bias-selectable. To overcome this, a quantum dot super-lattice infrared photodetector (SL-QDIP), which provides complete bias-selectability of the response peaks, is presented. The active region consists of two quantum dot super-lattices separated by a graded barrier, enabling photocurrent generation only in one super-lattice for a given bias polarity. According to theoretical predictions, a combined response due to three peaks at 2.9, 3.7, and 4.2 μm is expected for reverse bias, while a combined response of three peaks at 5.1, 7.8, and 10.5 μm is expected for forward bias.     

Transient Hole Trapping in Individual GeSi Quantum Dot Grown on Si（001） Studied by Conductive Atomic Force Microscopy

Electrical properties of individual self-assembled GeSi quantum dots grown on Si substrates are investigated by using conductive atomic force microscopy at room temperature. By controlling the bias voltage sweep in a certain fast sweep rate range, a novel current peak is observed in the current-voltage characteristics of the quantum dots. The current peaks are detectable only during the backward voltage sweep immediately after a forward sweep. The current peak position and intensity are found to depend strongly on the voltage sweep conditions. This kind of current-voltage characteristic under fast sweep is very different from the ordinary steady state current behaviour of quantum dots measured previously. trapping in the potential well formed bottom Si substrate. The origin of this phenomenon by the quantum dot sandwiched can be attributed to the transient hole between the native oxide layer and the     

High responsivity, LWIR dots-in-a-well quantum dot infrared photodetectors

In this paper we report studies on normal incidence, InAs/In_0.15Ga_0.85As quantum dot infrared photodetectors (QDIPs) in the dots-in-a-well (DWELL) configuration. Three QDIP structures with similar dot and well dimensions were grown and devices were fabricated from each wafer. Of the three devices studied, the first served as the control, the second was grown with an additional 400 Å AlGaAs blocking layer, and the third was grown on a GaAs n+ substrate with the intention of testing a single pass geometry. Spectral measurements on all three devices show one main peak in the long-wave IR (≈8 μm). The absorption was attributed to the bound-to-bound transition between the ground state of the InAs quantum dot and the ground state of the In_0.15Ga_0.85As well. Calibrated peak responsivity and peak detectivity measurements were performed on each device at 40, 60, and 80 K. For the same temperatures, frequency response measurements from 20 Hz to 4 kHz at a bias of V_b=−1 V were also performed. The addition of the blocking layer was shown to slightly enhance responsivity, which peaked at 2.4 A/W at 77 K, V_b=−1 V and responsivity was observed to be significantly reduced in the single pass (n+ substrate) sample. The rolloff of the frequency response was observed to be heavily dependent on temperature, bias, and irradiance. The results from the characterization of each sample are reported and discussed.     

PHOTOLUMINESCENCE STUDY OF InAs/GaAs SELF-ORGANIZED QUANTUM DOTS WITH BIMODAL SIZE DISTRIBUTION

We have investigated the temperature dependence of the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy image for uncapped sample. The power-dependent PL study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. Due to lacking of the couple between quantum dots, an unusual temperature dependence of the linewidth and peak energy of the dot ensemble photoluminescence has not been observed. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 μm at room temperature.     

Resonant magnetotunneling through individual self-assembled InAs quantum dots

A single-barrier GaAs/AlAs/GaAs heterostructure, with self-assembled In-based quantum dots incorporated in the AlAs tunnel barrier, exhibits a series of resonant peaks in the low temperature current–voltage characteristics. We argue that each peak arises fromsingle-electrontunneling through thediscrete zero-dimensionalstate of anindividualInAs dot. We use the tunneling for fine probing of the local density of states in the emitter-accumulation layer. Landau-quantized states are resolved at magnetic field B∥ as low as 0.2 T. Spin-splitting of the dot electron states has been observed forB⊥I.     

Electroluminescence spectra of an STM-tip-induced quantum dot

We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed, that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and the tunneling current. We find, in agreement with experiment, that increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the electron tunneling current through the STM-tip reveal a blue shift.     

Lifetime of resonant state in a spherical quantum dot

This paper calculates the lifetime of resonant state and transmission probability of a single electron tunnelling in a spherical quantum dot (SQD) structure by using the transfer matrix technique. In the SQD, the electron is confined both transversally and longitudinally, the motion in the transverse and longitudinal directions is separated by using the adiabatic approximation theory. Meanwhile, the energy levels of the former are considered as the effective confining potential. The numerical calculations are carried out for the SQD consisting of GaAs/InAs material. The obtained results show that the bigger radius of the quantum dot not only leads significantly to the shifts of resonant peaks toward the low-energy region, but also causes the lengthening of the lifetime of resonant state. The lifetime of resonant state can be calculated from the uncertainty principle between the energy half width and lifetime.     

Integral and local density of states of InAs quantum dots in GaAs/AlGaAs heterostructure observed by ballistic electron emission spectroscopy near one-electron ground state

Density of states is studied by a ballistic electron emission microscopy/spectroscopy on self-assembled InAs quantum dots embedded in GaAs/AlGaAs heterostructure prepared by metal–organic vapor phase epitaxy. An example of integral quantum dot density of states which is proportional to superposition of a derivative of ballistic current–voltage characteristics measured at every pixel (1.05 nm×1.05 nm) of quantum dot is presented. For the two lowest observed energy levels of quantum dot (the maxima in density of states) the density of states is mapped and correlated with the shape of quantum dot. It was found that prepared quantum dots have a few peaks on their flatter top and a split of the lowest energy level can be observed. This effect can be explained by inhomogeneous (nonuniform) stress distribution in the examined quantum dot.     

一种基于室温工作的量子点光电探测器的微光读出和应用研究

针对量子点光电探测器线列进行微光检测研究,量子点探测器采用AlAs/GaAs/AlAs双势垒结构,GaAs宽阱中分别有一个InAs量子点(QDs)和In_0.15Ga_0.85As量子阱(QW),建立一个简单的器件模型进行分析。常温下,在632.8 nm He-Ne激光照射下,当光功率为 0.01 pW时,器件偏压-0.5 V,积分时间80.2 μs,电压响应率达到7.0×1011 V·W-1,具有非常高的灵敏度,这种光电探测器在300 K温度下可以探测光功率小于10-14 W极弱光。以这种量子点光电探测器为核心研制的高灵敏度光谱仪和分子超光谱系统结合对生物组织样本进行检测,研制了一种图谱相互验证,互为校正的生物组织光谱测量系统。     

Imaging and spectroscopy of artificial-atom states in core/shell nanocrystal quantum dots.

Current imaging scanning tunneling microscopy is used to observe the electronic wave functions in InAs/ZnSe core/shell nanocrystals. Images taken at a bias corresponding to the s conduction band state show that it is localized in the central core region, while images at higher bias probing the p state reveal that it extends to the shell. This is supported by optical and tunneling spectroscopy data demonstrating that the s-p gap closes upon shell growth. Shapes of the current images resemble atomlike envelope wave functions of the quantum dot calculated within a particle in a box model.