TEM study of the structure of GaAs on vicinal Si (001) surface grown by MBE

Molecular beam epitaxy (MBE) grown GaAs films on Si substrates (0 0 1) 4° off towards 1 1 1 A and towards 1 1 1 B, were examined by means of transmission electron microscopy (TEM). The results indicate that in both samples, threading dislocations in the GaAs epilayer are blocked mainly in a thin layer near the GaAs-Si interface. This thin layer is like an inner interface, consisting of pyramidal islands and is flatter on the As growth surface than that on the Ga growth surface. In the type B sample, the density of dislocations is lower, the inner interface is flatter and the number of twins is much larger than that in the type A sample.     

MBE方法在GaAs(001)衬底上外延生长GaSb膜

利用分子束外延方法(MBE)在GaAs(001)衬底上外延生长了GaSb薄膜,利用高分辨透射电子显微镜(HRTEM)、原子力显微镜(AFM)、Hall效应(HallEffect)和低温光荧光谱(LTPL)等手段对薄膜的晶体质量、电学性能和光学质量进行了研究。发现直接生长的GaSb膜表面平整,空穴迁移率较高。引入GaSb/AlSb超晶格可有效阻断进入GaSb外延层的穿通位错,对应的PL谱强度增强,材料的光学质量变好。     

Growth dynamics of GaAs on a vicinal surface of GaAs(100) in migration-stimulated epitaxy: Computer simulation

A computer simulation is made of growth of III–V binary compound semiconductors from fluxes of dimer anions and atomic cations to study the time dependences of the average height and roughness of GaAs films for various conditions of growth by migration-stimulated epitaxy on a vicinal surface of GaAs(100). Pis’ma Zh. Tekh. Fiz. 23, 61–70 (February 26, 1997)     

MBE生长InGaAs/GaAs(001)多层矩阵式量子点

用分子束外延(MBE)设备以Stranski-Krastanov(S-K)生长模式,通过间歇式源中断方式外延生长了多个周期垂直堆垛的InGaAs量子点,首次获得大小及密度可调的In0.43Ga0.57As/GaAs(001)矩阵式量子点DWELL结构。样品外延结构大致为500nm的GaAs、多个周期循环堆垛InGaAs量子点和60ML的GaAs隔离层等。生长过程中用反射式高能电子衍射仪(RHEED)实时监控,样品经退火后使用扫描隧道显微镜(STM)进行表面形貌的表征。     

MBE生长GaAs(001)薄膜表面的Ostwald熟化过程研究

采用带有RHEED的MBE技术,利用RHEED图像演变实时监控薄膜生长状况,通过RHEED强度振荡测算薄膜生长速率,在GaAs(001)基片上同质外延GaAs薄膜。利用STM对MBE生长的GaAs薄膜表面的熟化过程进行了深入研究。研究发现,随着退火时间的延长,刚完成生长的GaAs表面从具有大量岛和坑的粗糙表面逐渐熟化,在熟化过程中岛不断合并扩大并与平台结合,而坑却逐渐消失。指出当熟化过程完成后GaAs表面将进入原子级平坦状态,并详细解释了熟化过程GaAs表面各种形貌特征形成的内在原因。     

Vertically standing Ge nanowires on GaAs(110) substrates

The growth of epitaxial Ge nanowires is investigated on (100), (111) B and (110) GaAs substrates in the growth temperature range from 300 to 380?°C. Unlike epitaxial Ge nanowires on Ge or Si substrates, Ge nanowires on GaAs substrates grow predominantly along the [Formula: see text] direction. Using this unique property, vertical [Formula: see text] Ge nanowires epitaxially grown on GaAs(110) surface are realized. In addition, these Ge nanowires exhibit minimal tapering and uniform diameters, regardless of growth temperatures, which is an advantageous property for device applications. Ge nanowires growing along the [Formula: see text] directions are particularly attractive candidates for forming nanobridge devices on conventional (100) surfaces.     

MBE生长GaAs薄膜表面形貌的RHEED图样研究

本文通过在GaAs(100)单晶衬底上MBE生长GaAs过程中形成的RHEED衍射图样,对GaAs薄膜的表面形貌进行研究。分析GaAs表面粗糙和生长时不发生RHEED强度振荡的原因。讨论在生长GaAs时出现In(Ga)As/GaAs(100)体系的RHEED衍射图样这种异常现象的原因。     

Peculiarities of the MBE growth of nanowhiskers on GaAs(100) substrates

We have studied the formation of nanowhiskers (NWs) by molecular beam epitaxy (MBE) on GaAs(100) substrates. The MBE growth of NWs exhibits two stages (initial and developed) and leads to the formation of NWs with surface morphology of two types (nucleation and intergrowth). The stage of developed growth is characterized by the predominant formation of intergrown NWs oriented in the 〈111〉B direction, having (110) habit (including the NW tip surface) and hexagonal cross sections with a transverse size within 50–300 nm. It was found that the transverse size of a hexagonal NW may significantly differ from that of an Au-GaAs melt droplet. The ratio of longitudinal and transverse dimensions of intergrown NWs can be on the order of 150 and above. When the transverse size of NWs exceeds a certain value (about 200 nm), the crystal length exhibits a slight decrease. The existence of two types of morphology is indicative of inhomogeneous character of the NW growth on a GaAs(100) surface, which depends on the catalyst droplet size, effective thickness of the deposited GaAs layer, and the growth temperature.     

Growth dynamics of GaAs, AlAs and (Al, Ga)As on GaAs (110) and (111)A substrates during molecular beam epitaxy

The growth dynamics of GaAs, AlAs and (Al, Ga)As films grown by molecular beam epitaxy (MBE) on GaAs(110) and (111)A substrates have been studied using reflection high energy electron diffraction (RHEED) intensity oscillations and scanning tunnelling microscopy (STM). In contrast to growth on (001) oriented substrates, the period of the RHEED intensity oscillation does not in general provide a measure of the growth rate. This is explained by the very different surface chemistry involved, since the short lifetime of arsenic molecules (As₂ or As₄) on non-(001) surfaces results in cation-stable surface conditions, which generate arsenic (anion)- induced intensity oscillations, whereas on (001) surfaces they are cationinduced under all normal growth conditions. The effects of this behaviour on surface morphology are illustrated, as are the relative influences of Ga and Al. STM images obtained during the first few monolayers of growth provide a detailed indication of the growth mode and in particular explain in a simple manner the origin of bilayer period RHEED intensity oscillations obtained during growth on GaAs (110).     

Growth and intermixing of Nb on Fe(110) and Fe on Nb(110)

The growth system Nb/Fe and the reversed system Fe/Nb were studied on the (110) surface using Scanning Tunneling Microscopy (STM). For Nb/Fe(110) we present in situ STM results as a direct evidence of a Nb/Fe exchange mechanism at temperatures above 400 K that leads to the formation of a surface alloy.

Since the experiments on Nb(110) were done on Nb buffer layers the fabrication of those is discussed. We show that besides Al₂O₃ (112¯0) wafers a W(110) single crystal can serve as a support for Nb(110) buffer layers which is more convenient for STM measurements. The niobium oxide adlayer that is present on nearly all Nb surfaces can be avoided by thorough degassing of the Nb source.

Results on Fe/Nb(110) are discussed in the temperature range from room temperature (RT) to 1000 K. At RT no intermixing of Fe and Nb was observed and with very low deposition rates epitaxial films can be grown. An ordered dislocation network was observed in the first Fe layers. Above 800 K two adatom island species are present as the manifestation of an alloying process. The formation of an Fe–Nb surface alloy which in the submonolayer regime is interspersed with chains of pure Fe is suggested.     

Effect of nitridation on crystallinity of GaN grown on GaAs by MBE

GaN films are grown on [0 0 1] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. Films are evaluated by X-ray diffraction and the dependence of crystalline quality on the nitridation temperature is studied. It is demonstrated that nitridation has to be performed at low-temperature to achieve c-oriented α-GaN. Higher nitridation temperature promotes formation of mis-oriented domains and β-GaN inclusions     

Enhancement of the 2DEG density in AlGaAs/InGaAs/GaAs P-HEMTs structures grown by MBE on (311)A and (111)A GaAs substrates

The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al_0.33Ga_0.7As/In_0.1Ga_0.9As/GaAs have been grown by molecular beam epitaxy (MBE) on (311)A and (111)A GaAs substrates. The epitaxy of strain heterostructure on high index GaAs substrate has led to new growth phenomena, material properties and device applications. The photoluminescence (PL) spectra of the structures have been measured at low temperature. The dominant emission in the PL spectra is due to the recombination from the first electron (e1) subband to the first heavy-hole (hh1) subband (E₁₁: e1–hh1). This feature (E₁₁) is a relatively broad peak and has a typical asymmetric line shape. The transformation of the PL spectra in the close vicinity of the Fermi edge (E_F) under different excitation densities gives strong evidence for the Fermi Edge Singularity (FES) existence. The density of the quasi-two-dimensional electron gas (2DEG) determined by PL study (n_s^PL), is in sufficient agreement with the values found from Hall measurements n_s^Hall at 77 K. The results prove an increase of the electron density in sample grown on GaAs (111)A and (311)A rather than in equivalent sample grown on (001) GaAs substrate. This effect is in good agreement with our theoretical prediction, which is based on a self-consistent solution of the coupled Schrödinger and Poisson equations.     

Ab initio simulation of Si-doped GaAs(110) cross-sectional surfaces

We study different configurations of the (110) cross-sectional surface of Si-doped GaAs, from the isolated Si donor up to an entire donor–acceptor Si bilayer embedded along the (001) growth direction. Electronic potentials, density of electronic states, cross-sectional scanning tunneling microscopy (XSTM) images are calculated using first-principles numerical simulations. Doping configurations with compensating Si impurities in cationic and anionic sites, such as the donor–acceptor bilayer, are characterized by XSTM images with bright signal at negative bias, strongly attenuated when the bias is reversed. These features are characteristic of real samples above the onset of self-compensation. The comparison of the experimental images with the numerical simulations allows to shed light on the microscopic picture of self compensation hitherto associated to a variety of mechanisms – including the formation of complexes of Si with native defects – and to uniquely attribute the observed experimental features to Si donor–acceptor configurations.     

Origin of non-uniformity in MBE grown nanometer-sized InGaAs ridge quantum wires and its removal by atomic hydrogen-assisted cleaning

The origin of non-uniformity of MBE-grown InGaAs ridge quantum wires (QWRs) in sub 10-nm wire width range was investigated in detail by SEM, in situ XPS, TEM and PL measurements. InAlAs/InGaAs/InAlAs wires were selectively grown on InGaAs ridge structures prepared also by MBE on 10 stripe patterned (001) InP substrates. The main source of non-uniformity was thermal cleaning of InP in As₄ done prior to InGaAs ridge formation which produced ridges having irregular sized InGaAs islands due to an initial As–P exchange reaction. Low temperature atomic hydrogen cleaning removed this problem, and led to successful formation of sub 10-nm QWRs.     

InGaAs/GaAs异质薄膜的MBE生长研究

利用分子束外延技术,在GaAs(001)基片上外延InGaAs/GaAs异质薄膜,通过RHEED图像演变实时监控薄膜生长状况,采用RHEED强度振荡测量薄膜生长速率,确定薄膜中In/Ga的组分比,并提出控制InGaAs薄膜中In/Ga组分比的生长方法.根据RHEED图像,指出获得的InGaAs薄膜处于(2×3)表面重构...     

Growth of GaAs nanowhisker arrays by magnetron sputtering on Si(111) substrates

The growth of GaAs nanowhisker (NW) arrays on Si(111) substrates by magnetron sputtering is demonstrated. The characteristic NW length is proportional to the effective thickness of a deposited layer and inversely proportional to the transverse whisker size at the top. The results are explained in terms of the diffusion model of NW growth.     

Spatial Structure of a Single Mn Impurity State on GaAs (110) Surface

Using a low temperature scanning tunneling microscope (STM), we have manipulated individual Mn adatoms at the GaAs (110) surface to apparently bond with two surface As atoms. In this configuration the Mn atoms, which either are at an interstitial site or have substituted for a surface Ga atom, give rise to strong in-gap levels as probed by spatially resolved STM spectroscopy measurements. Mapping the Mn-induced in-gap bound state shows an unusual spatial structure, with highly anisotropic character. The bound state shares some characteristic features with subsurface Mn and Zn dopants.     

Mechanism of self-assembled growth of ordered GaAs nanowire arrays by metalorganic vapor phase epitaxy on GaAs vicinal substrates

We report the self-catalyzed growth of GaAs nanowire arrays by metalorganic vapor phase epitaxy (MOVPE) on GaAs vicinal substrates. The effect of substrate misorientation on the nanowire growth and the influence of growth parameters such as temperature and input V/III ratio have been studied in detail. Variation in the nanowire growth mechanism and consequential changes in the nanowire growth morphology were observed. A VLS growth mechanism with negligible effect of the vicinal surface gave rise to randomly distributed droplet-terminated GaAs nanowires at 400?°C and multiprong root-grown GaAs nanowire clusters at 500?°C with low V/III ratio. The substrate misorientation effect was dominant at 500?°C with higher V/III ratio, in which case the combined effect of the vicinal surface and the self-catalyzed Ga droplets assisted the realization of self-assembled and crystallographically oriented epitaxial nanowire arrays through the vapor-solid mechanism.