Electron beam pre-patterning for site-control of self-assembled InAs quantum dots on Inp surfaces

A site control technique for individual InAs quantum dots (QDs) formed by self-assembling has been developed, using scanning electron microscope (SEM) assisted nano-deposition and metal organic vapor phase epitaxy (MOVPE). In a first step we characterize a device with randomly distributed InAs QDs on InP, using resonant tunneling and transmission electron microscopy (TEM). Secondly, we use nano-scale deposits, created at the focal point of the electron beam on an InP based heterostructure, as “nano growth masks”. Growth of a thin InP layer produces nano-holes above the deposits. The deposits are removed by oxygen plasma etching. When InAs is supplied on this surface, QDs are self-assembled at the hole sites, while no InAs dots are observed in the flat surface region. A vertical single electron tunneling device is proposed, using the developed technique.     

Effects of growth interruption on the evolution of InAs/InP self-assembled quantum dots

We investigated the change in the structural and optical properties of InAs/InP quantum structures during growth interruption (GI) for various times and under various atmospheres in metalorganic chemical vapor deposition. Under AsH₃ + H₂ atmosphere, the mass transport for the 2D-to-3D transition was observed during the GI. Photoluminescence peaks from both quantum dots (QDs) and quantum wells were observed from the premature QD samples. The fully developed QDs showed the two distinct temperature regimes in the PL peak position, full width at half maximum (FWHM) and wavelength-integrated peak intensity. The two characteristic activation energies were obtained from the InAs/InP QDs: ∼10 meV for intra-dot excitation and 90 ∼ 110 meV for the excitation out of the dots, respectively. It was also observed that the QD evolution kinetics could be suppressed in PH₃ + H₂ and H₂ atmospheres. The proper control of GI time and atmosphere might be a useful tool to further improve the properties of QDs.     

Self‐Assembled InAs Quantum Dots on InP(001) for Long‐Wavelength Laser Applications

Self‐assembled InAs quantum dots (QDs) embedded in an InAlGaAs matrix were grown on an InP (001) using a solid‐source molecular beam epitaxy and investigated using transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. TEM images indicated that the QD formation was strongly dependent on the growth behaviors of group III elements during the deposition of InAlGaAs barriers. We achieved a lasing operation of around 1.5 µm at room temperature from uncoated QD lasers based on the InAlGaAs‐InAlAs material system on the InP (001). The lasing wavelengths of the ridge‐waveguide QD lasers were also dependent upon the cavity lengths due mainly to the gain required for the lasing operation.     

InAs/GaAs量子点材料和激光器

介绍了近年来长波长InAsG/aAs量子点材料的生长、结构性质和量子点激光器的研究进展。     

Annealing behavior of InAs/GaAs quantum dot structures

We investigate the annealing behavior of InAs layers with different thicknesses in a GaAs matrix. The diffusion enhancement by strain, which is well established in strained quantum wells, occurs in InAs/GaAs quantum dots (QDs). A shift of the QD luminescence peak toward higher energies results from this enhanced diffusion. In the case of structures where a significant portion of the strain is relaxed by dislocations, the interdiffusion becomes negligible, and there is a propensity to generate additional dislocations. This results in a decrease of the QD luminescence intensity, and the QD peak energy is weakly affected.     

Growth of Space Ordered 1.3μm InAs Quantum Dots on GaAs(100) Vicinal Substrates by MOCVD

用MOCVD技术在偏(1100)GaAs衬底上生长了发光波长在1.3μm的线状空间规则排列InAs量子点.光致发光实验表明,相对于正(100)衬底,偏(100)GaAs衬底上生长的InAs量子点具有更好的材料质量,光谱有更大的强度和更窄的线宽.为了得到发光波长为1.3μm的量子点,对比研究了不同In含量的InGaAs应力缓冲层(SBL)和应力盖层(SCL)的应力缓冲作用.结果表明,增加SCL中In含量能有效延伸量子点发光波长到1. 3μm,但是随着SBL中In的增加,发光波长变化不明显,并且材料质量明显下降.     

InAs/GaAs自组装量子点结构的能带不连续量

为确定异质结界面带阶,结合光致发光(PL)谱和深能级瞬态谱(DLTS)测量结果,利用有效质量近似理论,计算得到了InAs/GaAs自组装量子点结构的能带不连续量,其中导带不连续量ΔEc＝0.97 eV,价带不连续量ΔEv＝0.14 eV.     

用MOCVD在偏(100)GaAs基片上生长空间规则排列的1.3μm InAs量子点

用MOCVD技术在偏(1100)GaAs衬底上生长了发光波长在1.3μm的线状空间规则排列InAs量子点.光致发光实验表明,相对于正(100)衬底,偏(100)GaAs衬底上生长的InAs量子点具有更好的材料质量,光谱有更大的强度和更窄的线宽.为了得到发光波长为1.3μm的量子点,对比研究了不同In含量的InGaAs应力缓冲层(SBL)和应力盖层(SCL)的应力缓冲作用.结果表明,增加SCL中In含量能有效延伸量子点发光波长到1. 3μm,但是随着SBL中In的增加,发光波长变化不明显,并且材料质量明显下降.     

Tuning of electronic states in self-assembled InAs quantum dots using an ion implantation technique

We report the tunability of up to 150 meV of the ground state transition of self-assembled InAs quantum dots (QDs) using Mn ion implantation and subsequent annealing. Because of the exciton localization in the quantum dots, the photoluminescence efficiency (T=12K) of the quantum dot transition remains at 80% of its original value after implantation with a Mn dose of 1×10¹³ cm⁻²ions. Strong luminescence still remains at room temperature. At a high implantation dose (1×10¹⁵ cm⁻²) and rapid thermal annealing (700°C for 60s) about 25% of the QD luminescence intensity is recovered at T=12K.     

GaAs基上的InAs量子环制备

在分子束外延系统中,利用3nmGaAs薄盖层将InAs自组装量子点部分覆盖,然后在500°C以及As2气氛中退火一分钟,制成纳米尺度的InAs量子环。这一形成敏感地依赖于退火时的生长条件和生长InAs自组装量子点时的淀积量。InAs在GaAs表面的扩散以及同时发生的In-Ga互混控制着InAs量子环的形成。     

Stable Temperature Characteristics of InAs／GaAs Quantum Dots at Long Wavelength Emission

The time-resolved photoluminescence and steady photoluminescence (TRPL and PL) spectra on self-assembled InAs/GaAs quantum dots (QDs) are investigated. By depositing GaAs/InAs short period superlattices (SLs), 1. 48μm emission is obtained at room temperature. Temperature dependent PL measurements show that the PL intensity of the emission is very steady. It decays only to half as the temperature increases from 15 K to room temperature, while at the same time, the intensity of the other emission decreases by a factor of 5 orders of magnitude. These two emissions are attributed to large-size QDs and short period superlattices (SLs), respectively. Large-size QDs are easier to capture and confine carriers, which benefits the lifetime of PL, and therefore makes the emission intensity insensitive to the temperature.     

Effects of GaAs-spacer strain on vertical ordering of stacked InAs quantum dots in a GaAs matrix

Vertical ordering in stacked layers of InAs/GaAs quantum dots is currently the focus of scientific research because of its potential for optoelectronics applications. Transmission electron microscopy was applied to study InAs/GaAs stacked layers grown by molecular-beam-epitaxy with various thicknesses of GaAs spacer. Thickness dependencies of quantum dot size and their ordering were observed experimentally and, then, compared with the results of strain calculations based on the finite element method. The vertical ordering did occur when the thickness of the GaAs spacer was comparable with the dot height. The ordering was found to be associated with relatively large InAs dots on the first layer. Quantum dots tend to become larger in size and more regular in plane with increasing numbers of stacks. Our results suggest that the vertical ordering is not only affected by strain from the InAs dots on the lower layer, but by total strain configuration in the multi-stacked structure.     

Stacking number dependence of size distribution of vertically stacked InAs/GaAs quantum dots

Vertically stacked layer structure is useful for controlling the size distribution of quantum dots. The dependence of the size distribution of quantum dots on the stacking numbers is theoretically and experimentally investigated. We show that the size distribution of quantum dots decreases with increasing the stacking number, and it occurs drastically when the stacking number is changed from 1 to 2. The quantitative analysis on in-plane strain energy distribution is also performed for the explanation.     

InAs/GaAs多层堆垛量子点激光器的激射特性

利用固态源分子束外延技术,按S-K模式生长出五层堆垛InAs/GaAs量子点（QD）微结构材料. 用这种QD材料制成的激光器,内光学损耗为2.1cm-1,透明电流密度为15±10 A/cm2. 对于条宽100μm,腔长2.4mm的激光器（腔面未经镀膜处理）,室温下基态激射的波长为108μm,阈值电流密度为144A/cm2,连续波光功率输出达2.67W（双面）,外量子效率为63%,特征温度为320K. 研究了QD激光器翟激射特性,并对结果作了讨论.     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

InAs自组织生长量子点的电子俘获势垒

成功地用深能级瞬态谱（ＤＬＴＳ）研究了ＩｎＡｓ自组织生长的量子点电学性质,获得２．５原子层ＩｎＡｓ量子点电子基态能级在ＧａＡｓ导带底下约０．１３ｅＶ,该量子点在荷电状态发生变化时伴随有晶格弛豫,对应俘获势垒为０．３２ｅＶ．本工作也证明可以把量子点类比深中心进行研究．     

Electronic coupling and structural ordering of quantum dots using InAs quantum dot columns

In this article, recent investigations of vertically aligned quantum dot columns conducted at Stanford University are reviewed. The quantum dots are InAs in a matrix of GaAs. Both the quantum dots and quantum dot columns are formed through strain-induced islanding, without lithography. Two aspects of these columns are discussed. First, the electronic coupling of quantum dots within columns of up to ten quantum dots is demonstrated. The coupling is adjusted and improvements to a simple light-emitting diode are shown. Second, increased uniformity of a surface quantum dot layer is shown when a subsurface layer of these columns are used. The most impressive results occur when the columns contain a large number of islands. Reduced variations in average ensemble height and diameter, called size uniformity, and average nearest neighbor distances, called structural uniformity, are shown. A surface unit cell of islands is demonstrated and the lack of a surface lattice is discussed.     

InP基近红外波段量子线激光器的电致发光谱

制备了InP基近红外波段量子线激光器,在改变注入条件的室温连续电致发光谱测试中,观察到了不同于带填充效应的谱型变化.低激励时,高能峰先出现;随激励电流增加,高能峰减弱并随后消失,同时低能峰出现并激射.认为激光器随注入电流的增加表现出的这种特殊的激射谱,是由自组织纳米结构尺寸的不均匀分布引起的.     

多层InAs量子点的光致发光研究

采用MBE设备生长了多层InAs/GaAs量子点结构,测量了其变温光致发光谱和时间分辨光致发光谱.结果表明多层量子点结构有利于减小发光峰的半高宽,并且可以提高发光峰半高宽和发光寿命的温度稳定性.实验发现,加InGaAs盖层后,量子点发光峰的半高宽进一步减小,最小达到23.6 meV,并且发光峰出现红移.原因可能在于InGaAs盖层减小了InAs岛所受的应力,阻止了In组分的偏析,提高了InAs量子点尺寸分布的均匀性和质量,导致载流子在不同量子点中的迁移效应减弱.     

环境友好型InP量子点的合成及其发光性能的研究进展

在光电显示领域中,量子点发光二极管（quantumdotslight-emittingdiode,QLED）因其宽的光谱可调性、窄的半峰全宽、高的色纯度等优异性能而受到广泛关注,并被认为是下一代显示技术极为突出的候选者。目前,镉基QLED的红、绿、蓝三色发光性能已十分接近有机发光二级管的水平,但是镉元素对人体及环境具有严重的危害性。InP量子点具有较大的激子波尔半径、宽的光谱可调性（可覆盖整个可见光区）以及与镉基量子点相媲美的光电性质,而成为最有望替代镉基量子点的环境友好型量子点。因此,本文详细总结了近年来InP量子点的合成（核壳的结构、配体的选择等）与荧光性能及其QLED发光性能等方面的研究进展,并对InPQLED所面临的问题、挑战及其可行性解决方案进行了讨论和展望。