金属铝在半导体表面的吸附

本文采用集团模型,用自洽的EHT方法计算金属Al在Si(111)和GaAs(110)面上吸附的稳定的几何构型和电子态,结果表明,Al在Si(111)面的三度开位上的离子吸附比顶位的共价吸附更稳定,态密度与实验符合也更好,Al吸附在GaAs(110)面上,将取代表面Ga原子,形成AlAs,此时GaAs(110)面将恢复到不弛豫的理想位置。 关键词：     

GaAs(001)衬底上分子束外延生长立方和六方GaN薄膜

采用分子束外延方法在GaAs(001)衬底上生长出了03微米厚的GaN薄膜,X射线双晶衍射和室温光荧光测试结果表明,采用GaAs氮化表面作为成核层可获得高纯度立方GaN薄膜而采用AlAs氮化表面作为成核层可获得高纯度六方GaN薄膜.这一研究结果表明在GaAs衬底上生长GaN薄膜的相结构可以通过选择不同的成核层来控制. 关键词：     

P与GaAs(100)表面相互作用的温度效应

本文采用原位X射线光电子能谱、紫外光电子能谱、高分辨率电子能量损失谱和低能电子衍射技术,研究了温度对P与GaAs(100)表面相互作用的影响。结果表明,经退火后,室温下淀积于GaAs表面的非晶P大部分脱附,仅剩下少量无规分布于表面的P集团。集团中部分P与衬底Ga原子成键,另一部分P则以单质形式存在,继续提高温度退火,将使P集团中的P全部与衬底发生反应生成GaAsP薄层。在高温GaAs衬底上淀积P,将得到GaAsP固溶体薄层。这一薄层有望成为GaAs表面理想的钝化膜。 关键词：     

基于液滴外延技术变Al、Ga组分对GaAs表面液滴生长形貌的影响

液滴外延技术不仅适用于晶格失配,也适用于晶格匹配材料系统,且易于制备低维半导体结构,如低密度量子点、环等.本文研究了液滴外延法在GaAs表面进行不同Al、Ga组分的量子点生长.在实验中用反射式高能电子衍射仪(Reflection High Energy Electron Diffraction, RHEED)对样品进行原位监控.通过控制Al、Ga液滴的沉积速率来控制液滴同时沉积在衬底上形成的组分.研究发现,随着Al组分的增加,量子点逐渐变得密集,润湿角变低.在Al组分增高超过0.5之后,出现了大小不一的量子点,且量子点密度出现指数型增长.对此进行研究分析,给出了一个经验公式,并就现象进行了解释.     

Ga束流低温辅助清理GaAs衬底表面氧化物的研究

采用低流量Ⅲ族Ga束流在分子束外延中低温辅助清理GaAs衬底表面氧化物.采用高能电子衍射监控衬底表面氧化物清理过程并得出氧化物清理速率及氧化层对高能电子的吸收系数.根据清理速率对衬底温度依赖的Arrhenius关系,估算了Ga辅助清理过程中发生化学反应所需要的活化能.Ga束流辅助清理衬底表面氧化物技术在外延生长中具有实...     

Ga液滴沉积速率对GaAs/GaAs(001)量子双环形貌的影响

采用液滴外延法在GaAs (001)衬底上制备同心量子双环(concentric quantum double rings, CQDRs),利用原子力显微镜表征其表面形貌,并研究Ga液滴沉积速率对CQDRs的影响.研究结果发现,随着Ga液滴沉积速率的增加, CQDRs的密度增加,内外环半径均降低.根据成核理论中最大团簇密度和Ga液滴沉积速率之间的关系拟合出临界成核原子数目为5,表明在Ga液滴形成阶段时稳定的Ga原子晶核至少包含5个Ga原子;根据成核理论和拟合结果绘制成核过程状态转化图以深入理解Ga液滴形成过程.相关研究结果对液滴外延法制备密度可控的GaAs同心量子双环具有一定的指导意义.     

AI在GaAs(110)面上的吸附

用电荷自洽的EHMO方法研究了Al在GaAs(110)面上的吸附问题。比较了两种吸附构型,从能量极小的观点定出了稳定的吸附应为Al取代表面Ga原子,使Ga落在表面As的悬挂键上。还计算了电荷转移、成键情况和状态密度。 关键词：     

GaAs(111)衬底上生长的GaN的极性与生长方法和生长条件的关系

研究了在GaAs(111)衬底上生长的六角相GaN的极性的相关关系.在高Ⅴ/Ⅲ比的条件下用MOVPE和MOMBE方法生长的GaN的极性和GaAs衬底的极性一致;在(111)A-Ga表面上的生长层呈现Ga的极性,而在(111)B-As表面上的生长层呈现N的极性.然而,在低的Ⅴ/Ⅲ比,或采用一个AIN中间层的条件下,用HVPE和MOMBE方法在GaAs(111)B表面上生长的GaN呈现出Ga的极性.目前,其原因尚不清楚,但是这些结果表明采用HVPE生长方法或用一高温AlN阻挡层可以得到高质量的GaN.     

δ-掺杂Be受主GaAs/AlAs多量子阱的空穴共振隧穿（英文）

三个具有不同量子阱宽度的GaAs/AlAs多量子阱结构样品通过分子束外延生长设备生长在半绝缘的(100)p-型GaAs衬底上,并且在量子阱层结构的生长过程中,在GaAs阱层中央进行了Be受主的δ-掺杂。基于这3个结构样品,通过光刻技术和半导体加工工艺制备了相应的两端器件。在4～200 K的温度范围内,我们分别测量了器件的电流-电压特征曲线,清楚地观察到了重、轻空穴通过δ-掺杂Be受主GaAs/AlAs多量子阱结构的共振隧穿现象。发现随着GaAs量子阱层宽的逐渐减小,轻空穴的共振隧穿峰向着高电压方向移动,这个结果和通过AlAs/GaAs/AlAs双势垒结构模型计算的结果是一致的。然而,随着测量温度的进一步升高,两个轻空穴共振峰都朝着低电压的方向移动,并且在150 K温度下,其中一个共振遂穿峰表现为一种振动模式。     

垂直腔面发射激光器的结构生长及特性研究

在偏〈111〉A 2°的GaAs (100) 衬底上生长了Al0.9Ga0.1As /Al0.2Ga0.8As周期结构的垂直腔面发射激光器（VCSEL）外延片P 型DBR的周期数为24.5对,N型DBR的周期数为34.5对.用光荧光 (PL) 谱、扫描电子显微镜 (SEM)和X射线双晶衍射 (XRD) 方法对VCSEL的光学特性和结构特性进行了分析室温量子阱材料的PL谱峰值波长为837.0 nm,半高宽达到28.9 nm在X射线双晶衍射回摆曲线中,除了“0”级衍射峰外,还观察到一级和二级卫星峰.“0”级双晶衍射峰的半高宽为12.56弧秒(″),衬底GaAs的衍射峰半高宽为11.79″.“0”级衍射峰半高宽与衬底GaAs的衍射峰半高宽比较接近,表明晶格具有很高的完整性.实验结果表明腔模波长为837.2 nm,腔模波长与PL谱峰值波长相匹配.     

Surface mediated control of droplet density and morphology on GaAs and AlAs surfaces

We present a comparative study of gallium (Ga) and aluminium (Al) droplets fabricated on GaAs (100) and AlAs (100) surfaces. Higher density of Ga droplets is achieved on AlAs surface compared with GaAs surface. Similarly, the density of Al nanostructures is higher on AlAs surface than on GaAs surface, even though different morphologies are obtained on each surface. Further, while uniform Ga droplets are formed on both GaAs and AlAs surfaces, Al rings and dots, with big inhomogeneity, are observed on GaAs and AlAs surface, respectively. This investigation suggests that size and shape of nanostructures grown by the droplet epitaxy method can be designed by employing different surfaces. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Angular-resolved photoemission from GaAs(110) surfaces with adsorbed Al

GaAs(110) surfaces with adsorbed Al were studied by a combination of angular-resolved valence band photoemission, Ga 3d core level photoemission, low energy electron loss spectroscopy and Auger electron spectroscopy. At room temperature Al is adsorbed on top of GaAs. After heat treatment the compound AlAs is formed at the surface, which is used as a substrate for Ga adsorption to form the inverted structure of the system GaAs + Al.     

MBE growth of AlGaAs on patterned GaAs substrates

We have experimentally and theoretically investigated the molecular-beam epitaxy growth of AlGaAs layers on ridge structures of patterned GaAs(0 0 1) substrates. While the surface morphologies were imaged by scanning electron microscopy, the local Al concentrations were mapped by spatially resolved micro-photoluminescence spectroscopy. Both, the surface morphologies and the profiles of the Al concentration could be well modeled by calculations based on a rate-equation which accounts for the migration of Ga adatoms and for the different growth rates of GaAs and AlAs.     

Structural and optical properties of high-density (>10/cm) InAs QDs with varying Al(Ga)As matrix layer thickness

We have obtained high-density (>10¹¹/cm²) InAs quantum dot (QD) structures by using an Al(Ga)As matrix layer. With increase of the AlAs matrix layer thickness, the density of QDs increases a little and the luminescence intensity emitted from InAs QDs decreases. We have used a thin GaAs insertion layer (IL) for the reason of keeping InAs QDs from an aluminum intermixing towards QDs. As the thickness of GaAs IL increases, the density of QDs decreases slightly due to the reduction of the roughness of an AlAs matrix layer. However, the luminescence intensity increases with increase in the thickness of GaAs IL resulting from the efficient blocking of an aluminum intermixing towards QDs.     

Temperature and reconstruction dependence of the initial Al growth on GaAs(001)

The development of the interface between Al and MBE-grown GaAs(001) surfaces has been analyzed up to a mean Al coverage of 0.5 nm. Interdiffusion, chemical reactivity and nucleation have been studied by Auger electron spectroscopy and reflection high energy electron diffraction for the c(2 × 8) and the (4 × 6) surface reconstructions in the temperature interval 268 to 673 K. Above 550 K no nucleation was observed and the growth process was governed by As outdiffusion followed by formation of AlAs. At lower temperatures three characteristic regions of Al coverage were found. The different growth mechanisms in these regions are discussed. An AlGa exchange reaction was observed only on the Ga-rich (4 × 6) structure where it was also correlated to the nucleation. The particular deposition measurement procedure used was found to be an important parameter, since interdiffusion was observed even at room temperature. The coverage at which 3D nucleation occurred was dependent on both substrate temperature and surface reconstruction but always appeared between 1.5 and 3.5 monolayer coverage. A strong temperature dependence of the nucleation was observed.     

GaAs/AlAs super-flat interfaces in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells grown on (4 1 1)A GaAs substrates by MBE

Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs) (AlAs) QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width ( ) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs) (AlAs) QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs) (AlAs) QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7 7 mm ), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) QWs grown on the (4 1 1)A GaAs substrates.     

Oxide-apertured VCSEL with short period superlattice

Novel distributed Bragg reflectors (DBRs) with 4.5 pairs of GaAs/AlAs short period superlattice (SPS)used in oxide-apertured vertical-cavity surface-emitting lasers (VCSELs) were designed. The structure of a 22-period Al0.9Ga0.1As (69.5 nm)/4.5-pair [GaAs (10 nm)-AlAs (1.9 nm)] DBR was grown on an n+ GaAs substrate (100) 2° off toward (111)A by molecular beam epitaxy. The emitting wavelength was 850 nm with low threshold current of about 2 mA, corresponding to the threshold current density of 2 kA/cm2. The maximum output power was more than 1 mW. The VCSEL device temperature was increased by heating ambient temperature from 20 to 100 ℃ and the threshold current increased slowly with the increase of temperature.     

Multilayers as defect barriers

A multilayer structure consisting of undoped GaAs and AlAs layers was incorporated into a buffer layer on GaAs substrates. This reduces the spreading of impurities from the substrate (e.g. tellurium) into layers deposited on top of the multilayer system as observed by SIMS and C/V profiling. Incorporation coefficients for tellurium in GaAs, AlAs and multilayers were calculated.