Complex quantum ring structures formed by droplet epitaxy

Well-defined complex quantum ring structures formed by droplet epitaxy are demonstrated. By varying the temperature of the crystallizing Ga droplets and changing the As flux, GaAs/AlGaAs quantum single rings and concentric quantum double rings are fabricated, and double-ring complexes are observed. The growth mechanism of these quantum ring complexes is addressed. (c) 2006 American Institute of Physics.

Flip-chip bonded hybrid CMOS/SEED optoelectronic smart pixels

Hybrid integration of GaAs/AlGaAs multiple quantum well self electro-optic effect device (SEED) arrays are demonstrated flip-chip bonded directly onto 1 mu m silicon CMOS circuits. The GaAs/AlGaAs MQW devices are designed for 850 nm operation. Some devices are used as input light detectors and others serve as output light modulators. The measurement results under applied biases show good optoelectronic characteristics of elements in SEED arrays. Nearly the same reflection spectrum is obtained for the different devices at an array and the contrast ratio is more than 1.2:1 after flip-chip bonding and packaging. The transimpedance receiver-transmitter circuit can be operated at a frequency of 300 MHz.

Observation of field-driven blue shift in delta-doped Si n-i-p-i multiple quantum wells

We report the observation of the field-driven blue shift at near absorption edge in the photo-current response spectra of delta-doped Si n-i-p-i multiple quantum wells due to the widening of the effective energy gap. This phenomenon differs from the observed results in GaAs/AlGaAs and GeSi/Si superlattices, because the physical mechanisms of forming energy band in these superlattice samples are different. Our experimental results are interpreted satisfactorily by the theoretical calculation. (C) 1999 Elsevier Science Ltd. All rights reserved.

A new interface anisotropic potential of zinc-blende semiconductor interface induced by lattice mismatch

A new interface anisotropic potential, which is proportional to the lattice mismatch of interfaces and has no fitting parameter, has been deduced for (001) zinc-blende semiconductor interfaces. The comparison with other interface models is given for GaAs/AlAs and GaAs/InAs interfaces. The strong influence of the interface anisotropic potential on the inplane optical anisotropy of GaAs/AlGaAs low dimensional structures is demonstrated theoretically within the envelope function approximation.

Intrawell and interwell transfer of excitons in growth-interrupted quantum wells

Intrawell and interwell transfers of excitons are observed by a temperature-dependent continuous-wave photoluminescence study of growth-interrupted single quantum wells. The intrawell transfer among the interface localization areas suggests a thermodynamic equilibrium between energy relaxation via LO-phonon emission and thermal population via phonon absorption. Thermal population is dominant in wider wells while relaxation is clearly observable in a four-monolayer narrow well at low temperatures. Interwell transfer of excitons also occurs between two narrow wells. (C) 1998 Academic Press.

A Photovoltaic InAs Quantum-Dot Infrared Photodetector

A photovoltaic quantum dot infrared photodetector with InAs/GaAs/AlGaAs structures is reported. The detector is sensitive to normal incident light. At zero bias and 78 K, a clear spectral response in the range of 2 -7 mu m has been obtained with peaks at 3.1, 4.8 and 5.7 mu m. The bandgap energies of GaAs and Al0.2Ga0.8As at 78K are calculated and the energy diagram of the transitions in the Quantum-Dot Infrared Photodetector (QDIP) is given out. The photocurrent signals can be detected up to 110 K, which is state-of-the-art for photovoltaic QDIP. The photovoltaic effect in our detector is a result of the enhanced band asymmetry as we design in the structure.

Optical response in a quantum dot superlattice nanoring under a lateral electric field

The optical absorption of a GaAs/AlGaAs quantum dot superlattice nanoring (QDSLNR) under a lateral dc electric field and with magnetic flux threading the ring is investigated. This structure and configuration provides a unique opportunity to study the optical response of a superlattice under an inhomogeneous electric field, which is not easily realized for general quantum well superlattices (QWSLs) but naturally realized for QDSLNRs under a homogeneous lateral electric field. It has been shown that a lateral dc electric field gives rise to a substantial change of the optical absorption spectra. Under a low field, the excitonic optical absorption is dominated by a 1s exciton. And with the electric field increasing, the optical absorption undergoes a transition from 1s excitonic absorption to 0 excitronic WSL absorption. (The number of 0, and -1 and +1 below are WSLs index.) The -1 and the +1 WSLs corresponding to the maximum effective field can also be identified. Due to the inhomogeneity of the electric field, the peaks of the -1 and the +1 WSLs are diminished and between them there exist rich and complicated structures. This is in contrast to the general QWSLs under a homogenous electric field. The complicated structures can be understood by considering the inhomogeneity of the electric field along the ring, which results in the nearest-neighbor transition, the next-nearest-neighbor transition, etc., have a different value repectively, at different sites along the ring. This may give rise to multiple WSLs. We have also shown that the line shape of the optical absorption is not sensitive to the threading magnetic flux. The threading magnetic flux only gives rise to a slight diamagnetic shift. Thus the enhancement of the sensitivity to the flux allowing for observation of the excitonic Aharanov-Bohm effect in the plain nanoring is not expected in QDSLNRs.

ENHANCEMENT EFFECT OF PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED SIN CAPPING LAYER ON DIELECTRIC CAP QUANTUM-WELL DISORDERING

Quantum well disordering of GaAs/AlGaAs multiple quantum well(MQW) has been accomplished with only plasma enhanced chemical vapor deposited (PECVD) SiN cap layer growth. The amount of blue shift increases with SiN growing time. This result has been explained by the vacancy indiffusion during PECVD SiN growth. Rapid thermal annealing (RTA) of the sample after SiN cap layer growth at 850 degrees C for 35 s caused a larger amount of blue shift than those obtained without RTA. By considering the model of Al diffusion from AlGaAs barrier into GaAs QWs together with the result from photoluminescence (PL) measurement, Al diffusion coefficients were calculated. The Al diffusion coefficient due to PECVD SiN was estimated at about 3 x10(-17) cm(2)/s. It was possible to extract the effect of RTA on the QW disordering, which showed that the amount of the blue shift and the Al diffusion coefficient due only to RTA increases with SiN cap layer thickness as reported by Chi et al.(10))

双色量子阱红外探测器顶部光子晶体耦合层的设计优化

采用三维时域有限差分算法（3D-FDTD）对GaAs/AlGaAs量子阱红外探测器（QWIP）的顶部光子晶体光输入耦合层结构的电磁场分布进行了仿真分析,得到了多种不同周期、占空比、深度的二维光子晶体结构耦合效率及电磁场分布.探索了一种双色探测器的光子晶体光输入耦合层结构的设计思路,使之可对中波/长波或长波双色8/12μm同时提供较高的耦合效率.

解理面预处理方法对二次外延的影响

利用超晶格解理面方法制备定位生长的InAs量子线．首先以分子束外延技术在GaAs衬底上生长GaAs／AlGaAs超晶格，然后将样品取出外延系统进行解理，对解理面进行预处理之后在（110）解理面上进行二次外延．实验结果显示超晶格解理面的预处理方法对二次外延有重大影响，其中择优腐蚀比自然氧化更有利于量子线的定位生长，过高温度的脱氧除气会导致解理面的GaAs部分出现坑状结构，表明（110）面上的Ga原子容易脱附．同时，Ga原子在（110）面上的迁移长度比较大，原子的择优扩散方向为[001-bar]方向．

160×128元多量子阱长波红外焦平面探测器件研制

报道了新研制出的160×128元GaAs/AlGaAs多量子阱长波红外焦平面器件.使用MBE的方法在半绝缘的GaAs衬底上生长器件结构;开发了用普通光刻技术和离子束刻蚀法制备2D光栅技术,以及探测器芯片与读出电路互联技术.在77 K时测试,器件的平均峰值探测率D~*_λ=1.28×10~(10) cmW~(-1)Hz~(1/2),峰值波长为λ_p=8.1μm,截止波长为λ_c=8.47μm.器件的非盲元率≥98.8%,不均匀性10%.

一种长波长MOEMS可调谐滤波器的结构设计和分析

提出了一种微光机电系统（MoEMS）可调谐滤波器结构，该结构采用GaAs／AlGaAs作为下分布布拉格反射镜（DBR），GaAs和SiO_2／Si介质膜作为上DBR，空气作为腔．按照波分复用系统的性能要求对MOEMS可调谐滤波器各项参数，如带宽、峰值透射率、挠度和调谐速度等进行了分析和设计．研究了挠度和调谐速度与梁厚度、宽度、长度等参数的关系．结果表明挠度与长度成正方向变化，同梁厚度、宽度成反方向变化，而调谐速度与各参数的关系恰好相反．

分子束外延生长赝配高电子迁移率超高速微结构功能材料里深中心识别

应用深能级瞬态谱（DLTS）技术研究分子束外延（MBE）生长的high electron mobility transistors （HEMT）和Pseudomorphic high electron mobility transistors （P-HEMT）结构深中心行为。样品的DLTS谱表明，在HEMT和P-HEMT结构的n-AlGaAs层里存在着较大浓度（10~(15)-10~(17)cm~(-3)）和俘获截面（10~(-16)cm~2）的近禁带中部电子争阱。它们可能与AlGaAs层的氧含量有关。同时还观察到P-HEMT结构晶格不匹配的AlGaAs/InGaAs/GaAs系统在AlGaAs里产生的应力引起DX中心（与硅有关）能级位置的有序移动。其移动量可作为应力大小的一个判据，表明DLTS技术是定性识别此应力的可靠和简便的工具。

量子阱平面光学各向异性的偏振差分反射谱研究

在室温下用偏振差分反射谱技术观察到了GaAs/AlGs、InGaAs/GaAs和InGaAs/InP三种量子阱材料的平面光学各向异性。我们发现GaAs/AlGaAs量子阱1h→1e跃迁的偏振度与阱宽成反比，与InGaAs/InP量子阱的报道结果类似。Ga原子偏析引起的界面不对称可以很好地解释这种行为。与之相反，InGaAs/GaAs量子阱的光学各向异性倾向于与阱宽成正比，目前还不能很好地解释这种现象。

准连续5kW叠层激光二极管列阵

报导了5kW GaAs/AlGaAs叠层激光二极管列阵的制作过程和测试结果。通过金属有机物化学气相沉积方法实现分别限制单量子阱结构。1cm激光条的填充密度是70%。采用80个激光条叠层封装，激光条间距是0.5mm，功率密度达1.25kW/cm~2，峰值波长是809.0nm，谱线宽度是4.8nm。