Molecular Beam Epitaxial Growth Of GaAs Research Articles

Classification of in situ reflection high energy electron diffraction images by principal component analysis

The reflection high-energy electron diffraction (RHEED) method is widely used for the in situ observation of molecular beam epitaxy (MBE). This is because the RHEED pattern dynamically changes according to the growth conditions, such as surface temperature and material supply. However, to date, the RHEED pattern has been categorized and recognized based on the experience of the researcher. In this study, we investigated the classification of RHEED pattern datasets without using labeling by the principal component analysis method that reduces the dimensionality of the data. The RHEED images were successfully classified during the MBE growth of GaAs, demonstrating that unsupervised learning can be used to recognize RHEED patterns.

In situ X‐ray diffraction of GaAs/MnSb/Ga(In)As heterostructures

AbstractWe have investigated the growth by molecular beam epitaxy (MBE) of GaAs on MnSb. MnSb epilayers on GaAs(111), GaAs(001) and of thickness 50 nm were used as substrates for GaAs films. The MBE growth of GaAs was monitored in situ using synchrotron X‐ray diffraction and reflection high energy electron diffraction. We show data on strain relaxation and growth mode, and discuss the epitaxial relationship between GaAs(001) and MnSb(101).Schematic of the molecular beam epitaxy/X‐ray diffraction in situ experiment and typical 2D detector data, with GaAs(111) and MnSb(0001) diffraction features.

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

ChemInform Abstract: Molecular Beam Epitaxial Growth and Magnetotransport Properties of GaMnAs

AbstractReview: 65 refs.

Surface segregation of indium atoms during molecular beam epitaxy of InGaAs/GaAs superlattices on [formula omitted] GaAs substrates

We have investigated substrate off-angle dependence of surface segregation of In atoms during molecular beam epitaxy (MBE) of pseudomorphic In 0.08 Ga 0.92 As / GaAs superlattices (SLs) on ( n 1 1 ) A -oriented GaAs substrates ( n =3–5). Surface segregation length of the In atoms ( λ : 1/ e decay length of the In content profile along the growth direction) was characterized by high resolution X-ray diffraction (HRXRD) and low-temperature (11 K) photoluminescence (PL) measurements. λ obtained for the ( n 1 1 ) A SLs were 1.2–1.4 times longer than that ( λ = 1.57 nm ) for the simultaneously grown (1 0 0) SL, and the (4 1 1)A SL showed the longest λ of 2.16 nm. The obtained substrate off-angle dependence of the In segregation length is quite similar to the incorporation life-time ( τ c ) of Ga adatoms reported for MBE growth of GaAs on channeled (1 0 0) substrates, indicating that larger surface migration of Ga adatoms during MBE growth on ( n 1 1 ) A substrates causes enhanced surface segregation of In atoms in the ( n 1 1 ) A InGaAs system.

Mobile dislocation density and strain relaxation rate evolution during InxGa1−xAs∕GaAs heteroepitaxy

The kinetics of dislocation-mediated strain relaxation have been investigated during InxGa1−xAs∕GaAs molecular beam epitaxy growth. We use in situ curvature measurement to determine the film stress as a function of time during deposition. The relaxation behavior includes a temperature dependent initial relaxation stage which partially relieves the misfit strain, followed by a rapid strain relaxation which commences at a temperature independent thickness and proceeds at a comparable rate at all temperatures studied. We discuss these observations in terms of the mobile dislocation density evolution and the dependence of the strain relaxation rate on the driving force and temperature.

First-principles studies of kinetics in epitaxial growth of III-V semiconductors

We demonstrate how first-principles calculations using density-functional theory (DFT) can be applied to gain insight into the molecular processes that rule the physics of materials processing. Specifically, we study the molecular beam epitaxy (MBE) of arsenic compound semiconductors. For homoepitaxy of GaAs on GaAs(001), a growth model is presented that builds on results of DFT calculations for molecular processes on the beta2-reconstructed GaAs(001) surface, including adsorption, desorption, surface diffusion and nucleation. Kinetic Monte Carlo simulations on the basis of the calculated energetics enable us to model MBE growth of GaAs from beams of Ga and As_2 in atomistic detail. The simulations show that island nucleation is controlled by the reaction of As_2 molecules with Ga adatoms on the surface. The analysis reveals that the scaling laws of standard nucleation theory for the island density as a function of growth temperature are not applicable to GaAs epitaxy. We also discuss heteroepitaxy of InAs on GaAs(001), and report first-principles DFT calculations for In diffusion on the strained GaAs substrate. In particular we address the effect of heteroepitaxial strain on the growth kinetics of coherently strained InAs islands. The strain field around an island is found to cause a slowing-down of material transport from the substrate towards the island and thus helps to achieve more homogeneous island sizes.

Arsenic surface segregation during the molecular-beam epitaxial growth of GaAs embedded in wurtzite GaN

We report on the growth of a thin GaAs layer embedded in wurtzite GaN prepared on (0001) sapphire substrate by rf-plasma molecular-beam epitaxy. It was found that the As surface segregation during the growth of the GaN cap layer can be controlled by the growth parameters, i.e., the growth interruption and subsequent in situ annealing process implemented in this study. The arsenic profile of the cap layer was accurately evaluated using an empirical segregation model. The surface morphology was also investigated using atomic force microscopy.

Heterojunction and interface space charge effects on interstitial Be diffusion during molecular beam epitaxy (MBE) growth

High level Be incorporation and diffusion during MBE growth of GaAs(P+)/GaAs(N) homo and GaAs(P+)/AlGaAs(N) heterojunctions have been shown to be strongly affected by the interfacial heterojunction and space charge electric field for the first time. The onset of fast Be interstitial diffusion is determined mainly by the MBE growth temperature, and partially influenced by the III–V flux ratio. The experimental result indicates that the Be diffusion species at the MBE growth surface is indeed positively charged as predicted by the hole tunneling, surface implantation model, hence the Be diffusion species slow down in the presence of higher opposing space charge electric field.

A study of the kinetic rate equation model for simulations of molecular beam epitaxy crystal growth: temperature dependence of surface kinetic processes

In this paper, we have studied the rate equation model of Kariotis and Lagally that can be used for a computer simulation of molecular beam epitaxial (MBE) growth. The advantage of such a model is the high speed of calculations so that results can be obtained in a very short time. The model is based on a solution of kinetic rate equations that govern the time dependence of the concentration of islands of varying sizes and differing heights on the top of the surface during MBE growth. One of the results of this model is an expression for the time dependence of the coverage of each layer . Within the present approach the MBE growth mode is evaluated by a calculation of the RHEED (reflection high-energy electron diffraction) intensity I(t). Similarly a calculation of the interface width IW(t), which determines the roughness of the growing surface, serves to confirm the growth mode of the MBE structure. In original model of Kariotis and Lagally the MBE growth has been affected by an appropriate choice of a set of the RE input parameters describing the probability of various kinetic processes appearing on the surface during the growth. In order to make the model applicable to simulations of MBE growth at `real' growth parameters (substrate temperature and deposition), we have included the substrate temperature dependence of all surface kinetic processes in the model. In this manner, and including processes described in the text, we have created a qualitatively new model that describes the MBE growth more accurately. This model has been used to simulate the MBE growth of GaAs at different substrate temperatures. The results have been compared with MC simulations and give an agreement in coverage profile

Electron mobility in selectively Si-doped GaAs/N–Al0.3Ga0.7As quantum well heterostructures with super-flat interfaces grown on (411)A GaAs substrates by molecular beam epitaxy

Reduced roughness of GaAs/Al0.3Ga0.7As heterointerfaces formed on (411)A substrates by Molecular Beam Epitaxy (MBE) was confirmed by measuring Two Dimensional Electron Gas (2DEG) mobility in selectively Si doped GaAs/N–Al0.3Ga0.7As Quantum Well (QW) structures with 4, 6, 8, or 50-nm thick GaAs wells. Below a QW thickness (Lw) of 8 nm, the 2DEG mobility at 15 K was mainly determined by interface roughness scattering and rapidly decreases with decreasing well thickness. The 2DEG in the (411)A selectively doped QW sample with Lw=4 nm has 34% higher mobility (μ=32 500 cm2/Vs) at 15 K than that of the (100) sample simultaneously grown (24 200 cm2/Vs). Every (411)A sample with Lw≤8 nm has 24–34% higher 2DEG mobility than the (100) sample simultaneously grown. This result indicates that smoother GaAs/Al0.3Ga0.7As interfaces were realized on the (411)A substrates. The (411)A sample with the 50-nm thick well shows 84% higher 2DEG mobility than the (100) sample simultaneously grown and its mobility is not determined by interface roughness scattering but ionized impurity scattering, which may suggest that MBE growth of GaAs and AlGaAs on the (411) GaAs substrates reduces unintentional impurity incorporation.

Novel features of photoluminescence spectra from acceptor-doped GaAs: formation of acceptor—acceptor pair emissions and optical compensation effect

Abstract Low temperature photoluminescence measurements were carried out for acceptor-doped GaAs. Impurities were introduced by doping during molecular beam epitaxy (MBE) or liquid phase epitaxy (LPE) growth or by ion beam impingement into substrates using mass-separated ions. In the case of carbon incorporation, doping of mass-separated C + ions using a low energy ion beam was carried out during MBE growth of GaAs. Results revealed that just below the band edge emissions a large number of novel strong emissions are produced. These emissions were found to be totally missing in specimens prepared by conventional methods. Dual incorporation of acceptor and donor impurities indicated that these emissions are easily quenched by an extremely small amount of donor atoms, which is a principal reason for the absence of these emissions in previous samples. Most of these novel emissions were also obtained in InP, implying that these observations are ubiquitously established in the whole range of III–V compound semiconductors. It was concluded that for the comprehensive understanding of impurity properties in semiconductors, mass-separated impurity introduction into ultra pure substrates is essential to avoid this strong optical (and corresponding electrical) compensation effect induced by oppositely charged impurities. Taking this conclusion into consideration, we emphasize that the optical properties of doped semiconductors should be totally re-examined in a more detailed and systematic manner.

Theoretical study of atomic structures and dynamics on semiconductor surfaces

First-principles theoretical studies of atomic structures and dynamics on semiconductor surfaces are presented in order to microscopically understand the mechanisms of epitaxial growth and etching of semiconductor surfaces. We first determine the atomic structures of As-rich GaAs(001)-(2 × 4) surfaces and investigate the surface diffusion of Ga adatoms on the As-rich surface, which is one of the most important processes in molecular-beam epitaxial growth of GaAs. Then, to elucidate surfactant-mediated epitaxial growth on Si (001), the site exchange reaction between surfactants and growing atoms is investigated and the reduction of surface diffusion is discussed. Finally, the interaction of chlorines with the reconstructed GaAs(001) surfaces, which plays an essential role in etching, is investigated.

Reflectance anisotropy oscillations during MOCVD and MBE growth of GaAs (001)

GaAs (001) surfaces in both metalorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are studied under As stabilisation as well as during growth by reflectance anisotropy spectroscopy (RAS). During MBE growth reflection high energy electron diffraction (RHEED) measurements are performed simultaneously. As a consequence of the oscillating density of steps during island growth, time resolved RAS measurements show oscillations with monolayer periodicity in both epitaxial systems. In order to separate morphology related and surface reconstruction domain related contributions to RAS oscillations an anisotropic effective medium model is applied. In both MBE and MOVPE domains of reduced As coverage close to the island boundaries are found to be responsible for RAS oscillations. In MBE this typically results in oscillations between spectra belonging to (2 x 4) reconstructions of different mean As dimer density. In MOVPE the surface oscillates between states with an increased and a decreased concentration of Ga dimers while c(4 x 4)-like As dimers are still present.

Double period RHEED oscillations during MBE growth of GaAs and AlAs on the GaAs(110) surface

Molecular beam epitaxy (MBE) of GaAs and AlAs on the GaAs(110) surface has been studied in situ using reflection high-energy electron diffraction (RHEED). Additionally ex situ atomic force microscopy (AFM) has been employed to investigate the surface topography after the growth. During the growth complex RHEED oscillations with a single and a double period can be measured, depending on the diffraction feature that is monitored. The AFM images of the surface reveal mono- and bilayer high steps and islands, reflecting a layer-by-layer growth with the participation of both at the same time. A simple model that leads to a qualitative understanding of the experimental observation is presented.

Selective growth of micro GaAs dots on Si by molecular beam epitaxy

A two-dimensional array of GaAs dots embedded in micro-facet pits on Si(001) has been successfully formed by molecular beam epitaxy (MBE) utilizing both surface diffusion phenomena and beam-shadowing techniques. GaAs dots were formed on part of the sidewalls, {111} facet planes, of the reverse-tetrahedral shape Si facet structure. An array of square windows with SiO 2 etching mask was formed by conventional photolithography of a SiO 2/Si(001) substrate followed by anisotropic chemical etching with an etchant of ethylenediamine/pyrocatechol aqueous solution. The size of the square edges of the tetrahedrons is a few microns square. Scanning secondary electron microscope (SEM) observation showed reverse-tetrahedral shape corns surrounded by four micro-facet planes of the exact {111} planes having clear 〈110〉 edge line. Then, MBE growth of GaAs has been performed on the SiO 2/Si(001) substrates containing the array of these facet structure. It has been found that the difference in surface diffusion length of Ga between on SiO 2 mask and on Si{111} facet regions and As beam shadowing cause the selective area growth on Si{111} facets. SEM and cathodoluminescence (CL) observations showed that the crystalline quality of the embedded GaAs layers on sidewalls of the Si pit is comparable to that of bulk GaAs. Observation by anisotropic chemical etching also showed that GaAs layers selectively formed on the {111} facets are free from anti-phase boundaries.

Selective growth of micro GaAs dots on Si by molecular beam epitaxy

A two-dimensional array of GaAs dots embedded in micro-facet pits on Si(001) has been successfully formed by molecular beam epitaxy (MBE) utilizing both surface diffusion phenomena and beam-shadowing techniques. GaAs dots were formed on part of the sidewalls, {111} facet planes, of the reverse-tetrahedral shape Si facet structure. An array of square windows with SiO2 etching mask was formed by conventional photolithography of a SiO2/Si(001) substrate followed by anisotropic chemical etching with an etchant of ethylenediamine/pyrocatechol aqueous solution. The size of the square edges of the tetrahedrons is a few microns square. Scanning secondary electron microscope (SEM) observation showed reverse-tetrahedral shape corns surrounded by four micro-facet planes of the exact {111} planes having clear 〈110〉 edge line. Then, MBE growth of GaAs has been performed on the SiO2/Si(001) substrates containing the array of these facet structure. It has been found that the difference in surface diffusion length of Ga between on SiO2 mask and on Si{111} facet regions and As beam shadowing cause the selective area growth on Si{111} facets. SEM and cathodoluminescence (CL) observations showed that the crystalline quality of the embedded GaAs layers on sidewalls of the Si pit is comparable to that of bulk GaAs. Observation by anisotropic chemical etching also showed that GaAs layers selectively formed on the {111} facets are free from anti-phase boundaries.

Gas composition dependence of silicon nitride used as gallium diffusion barrier during GaAs molecular beam epitaxy growth on Si complementary metal oxide semiconductor

We have measured the effect of deposition parameters upon the utility of plasma enhanced chemical vapor depositon silicon nitride as a gallium diffusions barrier during molecular beam epitaxy growth of gallium arsenide on silicon submicron complementary metal oxide semiconductor electronics. It was found that the conditions under which the silicon nitride is deposited severely impact the ability of these films to be used as a diffusion barrier, with the most critical dependence upon the silane to nitrogen gas ratio.

Step bunching and step equalization on vicinal GaAs(001) surfaces

Terrace width distributions have been calculated from scanning tunneling microscopy (STM) images of molecular-beam epitaxy (MBE)-grown GaAs(001) surfaces misoriented by both 1° and 2° towards the (111)A direction. This analysis reveals a peak in the terrace width distribution at approximately 40–50 Å, regardless of the original miscut, with larger terraces forming in order to preserve the angle of vicinality. Growth of a tilted superlattice (TSL) improves the periodicity of the surface. A statistical analysis of the STM image of a 1° TSL capped with three monolayers of GaAs reveals a bell-shaped distribution of terrace widths with a peak at the average terrace width. These results suggest that MBE growth of vicinal GaAs(001) does not result in equalized steps but that the growth of a TSL does tend towards step equalization. The differences between these two growth regimes are discussed.

Structural and optical properties of self-assembled InGaAs quantum dots

A one step method for the production of quantum dots is presented. The method exploits the mismatch strain of molecular beam epitaxy (MBE) deposited InGaAs on GaAs to induce a transition from the two-dimensional growth mode to the three-dimensional (Stranski–Krastanow) growth mode. The cluster size is limited to quantum dimensions by precisely controlling the amount of InGaAs that is deposited in order to cause the growth mode transition. Very narrow lateral size distributions with standard deviations of 14% on the dot area have been obtained. Smooth MBE growth of GaAs over these clusters produces a layer of quantum dots, whose high quality and uniformity has been observed with transmission electron microscopy, atomic force microscopy, and photoluminescence (PL). The quantum dot PL intensity is enhanced compared to a reference quantum well. Resonances in photoluminescence excitation (PLE) spectra suggest that the density of states in these dots has minima close to zero between the quantum states, as expected for a zero-dimensional system .These PLE peaks shift with the detecting energy, showing that by changing the detecting energy, we are sampling different sizes of dots. The temperature dependence of the PL indicates that the onset energy of thermal quenching of quantum dots is enhanced by a factor of 2, as compared to a quantum well, due to the additional confinement. In all samples, there is virtually no overlap between the PL emission and the first PLE peak of the quantum dots.