含有AlGaAs插入层的InAs/GaAs三色量子点红外探测器

本文报道了采用分子束外延技术制备的三色InAs/GaAs量子点红外探测器. 器件采用nin型结构, 吸收区结构是在InGaAs量子阱中生长含有AlGaAs插入层的InAs量子点, 器件在77 K下的红外光电流谱有三个峰值: 6.3, 10.2和11 μm. 文中分析了它们的跃迁机制, 并且分别进行了指认. 因为有源区采用了不对称结构, 所以器件在外加偏压正负方向不同时, 光电流谱峰值的强度存在一些差异. 不论在正偏压或者负偏压下, 当偏压达到较高值, 再进一步增大偏压时, 都出现了对应于连续态的跃迁峰强度明显下降的现象, 这是由量子点基态与阱外连续态的波函数交叠随着偏压进一步增大而迅速减小导致的.     

分子束外延生长的(GaAs1－xSbx/InyGa1－yAs)/GaAs量子阱光致发光谱研究

报道了(GaAs_1-xSb_x/In_yGa_1-yAs)/Ga As量子阱结构的分子束外延生长与光致发光谱研究结果.变温与变激发功率光致发光谱的研究表明了此结构 为二型量子阱发光性质.讨论了光谱双峰结构的跃迁机制.通过优化生长条件，获得了室温1 31μm发光. 关键词： 分子束外延 量子阱 二型发光     

Self-assembly of InAs quantum dots on GaAs(001)by molecular beam epitaxy

Currently, the nature of self-assembly of three-dimensional epitaxial islands or quantum dots (QDs) in a lattice-mismatched heteroepitaxial growth system, such as InAs/GaAs(001) and Ge/Si(001) as fabricated by molecular beam epitaxy (MBE), is still puzzling. The purpose of this article is to discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale. First, the conventional kinetic theories that have traditionally been used to interpret QD self-assembly in heteroepitaxial growth with a significant lattice mismatch are reviewed briefly by examining the literature of the past two decades. Second, based on their own experimental data, the authors point out that InAs QD self-assembly can proceed in distinctly different kinetic ways depending on the growth conditions and so cannot be framed within a universal kinetic theory, and, furthermore, that the process may be transient, or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories. Third, the authors point out that, in all of these conventional theories, two well-established experimental observations have been overlooked: i) A large number of “floating” indium atoms are present on the growing surface in MBE InAs/GaAs(001); ii) an elastically strained InAs film on the GaAs(001) substrate should be mechanically unstable. These two well-established experimental facts may be highly relevant and should be taken into account in interpreting InAs QD formation. Finally, the authors speculate that the formation of an InAs QD is more likely to be a collective event involving a large number of both indium and arsenic atoms simultaneously or, alternatively, a morphological/structural transformation in which a single atomic InAs sheet is transformed into a three-dimensional InAs island, accompanied by the rehybridization from the sp²-bonded to sp³- bonded atomic configuration of both indium and arsenic elements in the heteroepitaxial growth system.     

高In组分InGaNAs/GaAs量子阱的生长及发光特性

采用分子束外延技术(MBE)在Ga As衬底上外延生长高In组分(40%)In Ga NAs/Ga As量子阱材料,工作波长覆盖1.3~1.55μm光纤通信波段。利用室温光致发光(PL)光谱研究了N原子并入的生长机制和In Ga NAs/Ga As量子阱的生长特性。结果表明:N组分增加会引入大量非辐射复合中心;随着生长温度从480℃升高到580℃,N摩尔分数从2%迅速下降到0.2%;N并入组分几乎不受In组分和As压的影响,黏附系数接近1;生长温度在410℃、Ⅴ/Ⅲ束流比在25左右时,In_(0.4)Ga_(0.6)N_(0.01)As_(0.99)/Ga As量子阱PL发光强度最大,缺陷和位错最少;高生长速率可以获得较短的表面迁移长度和较好的晶体质量。     

压电调制反射光谱研究GaAs/Al0.29Ga0.71As单量子阱

报道了压电调制反射测量系统的建立，应用该系统获得了势阱宽度分别为5nm和25nm的两个G aAs/Al_0.29Ga_0.71As单量子阱的压电调制反射谱. 从图谱中可以看 出，在室 温下能够较容易地分辨出和轻、重空穴相关联的子带跃迁. 在阱宽25nm的样品中还观察到了 自旋-轨道跃迁. 利用有效质量理论近似计算，对量子阱样品的图谱结构进行了指认，发现 实验值和计算值能够较好地符合. 关键词： 压电调制反射光谱 单量子阱 分子束外延     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

Dependence of current-voltage characteristics of pseudomorphic AlAs/In0.53a0.47s/InAs resonant tunneling diodes on quantum well widths

This paper studies the dependence of I-V characteristics on quantum well widths in AlAs/In_0.53Ga_0.47As and AlAs/In_0.53Ga_0.47As/InAs resonant tunneling structures grown on InP substrates. It shows that the peak and the valley current density in the negative differential resistance region are closely related with quantum well width. The measured peak current density, valley current densities and peak-to-valley current ratio of resonant tunneling diodes are continually decreasing with increasing well width.     

GaSb/GaAs复合应力缓冲层上自组装InAs量子点的生长

研究了GaSb/GaAs复合应力缓冲层上自组装生长的InAs量子点.在2ML GaSb/1ML GaAs复合应力缓冲层上获得了高密度的、沿［100］方向择优分布量子点.随着复合应力缓冲层中GaAs层厚度的不同,量子点的密度可以在1.2×10¹⁰cm^-2和8×10¹⁰cm^-2进行调控.适当增加GaAs层的厚度至5ML,量子点的发光波长红移了约25nm,室温下PL光谱波长接近1300nm. 关键词： 自组装量子点 分子束外延 Ⅲ-Ⅴ族化合物半导体     

High-density and narrow size-distribution InAs quantum dots formed by a modified two-step growth

We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density ($\sim $5.9$\times $10$^{10}$\,cm$^{ - 2})$ good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth (27.7\,meV) of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.     

High-density and narrow size-distribution InAs quantum dots formed by a modified two-step growth

We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density ($\sim $5.9$\times $10$^{10}$\,cm$^{ - 2})$ good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth (27.7\,meV) of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.     

High Performance AlGaAs Quantum Well Lasers with Low Beam Divergence Grown by Molecular Beam Epitaxy

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Molecular beam epitaxy growth of quantum devices

The inherent fragility and surface/interface-sensitivity of quantum devices demand fabrication techniques under very clean environment. Here, I briefly introduces several techniques based on molecular beam epitaxy growth on pre-patterned substrates which enable us to directly prepare in-plane nanostructures and heterostructures in ultrahigh vacuum. The molecular beam epitaxy-based fabrication techniques are especially useful in constructing the high-quality devices and circuits for solid-state quantum computing in a scalable way.     

Optimization of InAs/GaAs quantum-dot structures and application to 1.3-μm mode-locked laser diodes

The self-assembled growth of InAs/GaAs quantum dots by molecular beam epitaxy is conducted by optimizing several growth parameters, using a one-step interruption method after island formation. The dependence of photoluminescence on areal quantum-dot density is systematically investigated as a function of InAs deposition, growth temperature and arsenic pressure. The results of this investigation along with time-resolved photoluminescence measurements show that the com- bination of a growth temperature of 490℃, with a deposition rate of 0.02 ML/s, under an arsenic pressure of 1×10^-6 Torr （1 Torr = 1.33322×10^2 Pa）, provides the best compromise between high density and the photoluminescence of quantum dot structure, with a radiative lifetime of 780 ps. The applicability of this 5-layer quantum dot structure to high-repetition-rate pulsed lasers is demonstrated with the fabrication and characterization of a monolithic InAs/GaAs quantum-dot passively mode-locked laser operating at nearly 1300 nm. Picosecond pulse generation is achieved from a two-section laser, with a 19.7-GHz repetition rate.     

Bound polaron in quantum dot quantum well structures

The problem of bound polarons in quantum dot quantum well (QDQW) structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical (LO) and surface optical (SO) modes are derived in the framework of the dielectric continuum approximation. The electron--phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numerical results reveal that there exist three branches of eigenfrequencies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.     

高灵敏度InAs/AlSb量子阱的霍尔器件(英文)

用分子束外延在Ga As(001)衬底上生长了两个量子阱结构的霍尔器件,一个是没有掺杂的量子阱结构,一个是Si-δ掺杂的量子阱结构。研究了霍尔器件的面电子浓度和电子迁移率与温度的关系。结果表明,在300 K下,Si-δ掺杂的量子阱结构的电子迁移率高达25 000 cm~2·V~(-1)·s~(-1),并且该器件输入电阻和输出电阻较低。同时,Si-δ掺杂的量子阱结构霍尔器件的敏感度好于没有掺杂的量子阱结构霍尔器件。     

InAs/GaSb量子阱中太赫兹光电导特性

太赫兹技术由于具有重大的科学价值及应用前景而引起了广泛关注,其核心问题是性能优异的室温太赫兹辐射源和探测器研究.本文用半经典的玻尔兹曼方程方法研究了In As/Ga Sb量子阱系统中载流子对电磁场的响应,运用平衡方程方法求解玻尔兹曼方程得到了量子阱系统中的光电导,系统地研究了量子阱结构对光电导的影响,揭示了在该量子阱系统中光电导产生的物理机制.研究发现,量子阱结构主要通过调节载流子的能级、浓度和波函数的耦合影响光电导,对称性较好的量子阱结构(8 nm-8 nm)的光电导信号更强,其峰值落在太赫兹区(0.2 THz),并且在低温下器件的性能较好,温度升高则吸收峰略有降低,且光电导峰值发生红移.研究结果表明该量子阱系统可以用作室温太赫兹光电器件.     

From magnetically doped topological insulator to the quantum anomalous Hall effect

Quantum Hall effect （QHE）, as a class of quantum phenomena that occur in macroscopic scale, is one of the most important topics in condensed matter physics. It has long been expected that QHE may occur without Landau levels so that neither external magnetic field nor high sample mobility is required for its study and application, Such a QHE free of Landau levels, can appear in topological insulators （TIs） with ferromagnetism as the quantized version of the anomalous Hall effect, i.e., quantum anomalous Hall （QAH） effect. Here we review our recent work on experimental realization of the QAH effect in magnetically doped TIs. With molecular beam epitaxy, we prepare thin films of Cr-doped （Bi,Sb）2Te3 TIs with well- controlled chemical potential and long-range ferromagnetic order that can survive the insulating phase. In such thin films, we eventually observed the quantization of the Hall resistance at h/e2 at zero field, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect provides a foundation for many other novel quantum phenomena predicted in TIs, and opens a route to practical applications of quantum Hall physics in low-power-consumption electronics.     

有机多层量子阱的能量转移

采用多源有机分子气相沉积系统制备了不同类型的有机多量子阱结构，利用电化学循环伏安法和吸收光谱、荧光光谱研究了量子阱的类型、光致发光的特性.电化学循环伏安法和吸收光谱的测量结果表明，PBD/8-羟基喹啉铝(Alq₃)有机量子阱为Ⅰ型量子阱结构，NPB/Alq₃和BCP/Alq₃有机量子阱为Ⅱ型量子阱结构.荧光光谱的研究结果表明，PBD/Alq₃和BCP/Alq₃量子阱结构可以实现PBD，BCP向Alq₃能量完全转移，而NPB/Alq₃量子阱结构，NPB和Alq₃之间只是部分能量转移.文中对影响能量转移的因素进行了讨论. 关键词： 有机量子阱 能量转移