Beam Epitaxial Growth Of GaAs Research Articles

Indium-induced smoothing of GaAs films during MBE growth

A new technique is reported for obtaining a smooth growth surface during molecular beam epitaxy growth of GaAs on (001) GaAs substrates. The smoothing is achieved by exposing the surface to an indium flux during growth of the GaAs buffer layer at high substrate temperature (590 °C). In situ light scattering shows a dramatic reduction in surface roughness along the [110] direction during this process, consistent with ex situ scanning force microscopy measurements on the films, which reveal atomically flat terraces oriented along the <110> directions. The surface reconstruction shifts from (2 × 4) to (4 × 2) under the indium flux, as revealed by reflection high-energy electron diffraction. The sticking coefficient of the indium as determined by secondary-ion mass spectroscopy is less than 10%. We attribute the observed effects to a transition from group V to group III termination, induced by surface segregation of the nonincorporated indium.

Dynamical Monte Carlo studies of molecular beam epitaxial growth models: interfacial scaling and morphology

We have modeled molecular beam epitaxial growth by d = 2 + 1 solid-on-solid models using dynamical Monte Carlo simulations. The chosen parameters are representative values of those derived from experimental molecular beam epitaxial growth of GaAs(100), and simulations were carried out over the experimentally relevant range of independent variables. We discuss the effects of growth temperature, transient mobility of incoming particles and Schwoebel barriers on the evolution of surface morphology and interfacial roughness. The interfacial properties are measured by the interfacial width, kink density, and reflection high-energy electron diffraction intensity at the out-of-phase condition. The temporal effective growth exponent, β eff, calculated as a function of temperature, shows a crossover from growth by random deposition at low temperature ( β eff = 0.5) to Edwards-Wilkinson growth at high temperature ( β eff = 0). A small plateau is observed at intermediate temperatures, at which β eff ≈ 0.22. Increasing the transient mobility of a precursor state (“hot” precursor) at low temperature also leads to a crossover from growth by random deposition to Edwards-Wilkinson growth, and β eff as a function of transient migration probability may show a plateau around β eff ≈ 0.25. However, increasing the Schwoebel barrier leads to a crossover from layer-by-layer growth to three-dimensional growth with β eff = 0.5 at high surface temperature. We also discuss these results qualitatively within the context of a coarse-grained description.

Secondary electron imaging of nucleation and growth of GaAs

In situ scanning electron microscopy was used for real-time imaging of surface morphology evolution during molecular beam epitaxial growth of GaAs. This method is characterized by a resolution that is high enough to resolve nucleated islands, and a high sensitivity to atomic layers. Electron-beam damage was avoided by reducing the primary beam current to 0.1–0.3 nA. Different growth stages, i.e. nucleation delay, nucleation of islands, coalescence of islands and monolayer completion, are clearly imaged during monolayer growth. The surface roughens with increases in the nucleation-coalescence cycle, and recovers its initial smoothness during post-growth annealing.

Distinguishing the As- or Ga-rich initial reconstruction in short-pulse supersonic nozzle beam epitaxy of GaAs in real time by millisecond time-resolved reflectance difference

For short-pulse supersonic nozzle beam epitaxy growth of GaAs on an As-rich initial surface, we measured the fast evolutions of As dimer density and Ga dimer density in real time by using a millisecond time-resolved reflectance difference (RD) system. Under the impingement of a trimethylgallium short pulse, the (2×4)β, (2×4)γ, and c(4×4) initial reconstructed surfaces show very different transient RD signals which can be used to distinguish the initial reconstruction of the GaAs surface in real time during the epitaxy.

Determination of the excess surface arsenic concentration in the metalorganic molecular beam epitaxial growth of GaAs using TMGa and As2

We report an in situ dynamic method for the determination of the surface concentration of adsorbed arsenic in the metalorganic molecular beam epitaxial growth of GaAs from trimethylgallium (TMGa) and As2. Changes in the reflection high electron energy diffraction intensity oscillation period are observed under arsenic limited conditions, in which the decomposition of TMGa is strongly mediated by adsorbed arsenic. The period of the oscillations at the onset of growth indicates a time dependence in which the period gradually increases from the first oscillation to a steady state value after the growth of several monolayers. The results are interpreted as being due to an initial excess arsenic coverage which acts as a secondary source in this growth regime.

Surface processes responsible for reflectance-anisotropy oscillations during molecular beam epitaxy growth of GaAs(001)

Reflectance anisotropy spectroscopy (RAS) oscillations during molecular beam epitaxy (MBE) growth of singular GaAs(001) were studied at substrate temperatures between 500°C and 610°C. RAS spectra were measured and related to surface reconstructions determined by reflection high-energy electron diffraction (RHEED). The RAS signal sensitively monitors surface changes when growth is initiated. With opening of the Ga shutter an immediate change in the RAS response indicates the modified As adsorption/desorption equilibrium due to the presence of Ga atoms on the surface. During growth of the first GaAs monolayers RAS oscillations mirror the oscillation of the monolayer step density in island growth mode. From all experimental evidence it must be concluded that the step density modulates the As dimer coverage because As desorbs predominantly in regions close to the island boundaries.

Theoretical investigation of adsorption behavior during molecular beam epitaxy growth of GaAs: ab initio based microscopic calculation

This paper investigates, theoretically, the migration potential and adsorption energies of Ga adatoms on a reconstructed As-rich GaAs (001)-(2 × 4) surface by ab initio calculation. The calculated results show that migration potential depends sensitively on the number of surface Ga adatoms and that the adsorption energy oscillates with the adsorption of every other atom. The dependence on the number of surface Ga atoms is explained by the effects of the surface distortion and the electron counting model. This paper also discusses As incorporation during epitaxial growth and demonstrates the dynamical behavior of Ga adatoms at finite temperature by Monte-Carlo simulation.

Theoretical investigation of adsorption behavior during molecular beam epitaxy growth of GaAs: Ab initio based microscopic calculation

Theoretical investigation of adsorption behavior during molecular beam epitaxy growth of GaAs: Ab initio based microscopic calculation

Tin as an n-type dopant in the molecular beam epitaxial growth of GaAs(111)A

We have made a systematic study of the tin doping of GaAs layers grown on GaAs(111)A substrates using molecular beam epitaxy (MBE). A series of samples were grown with a range of substrate temperatures (from 460 to 620°C), As:Ga flux ratios (5:1 to 25:1) and tin concentrations (10 16 to 10 20 atoms cm −3 ). Layers grown on (111)A surfaces were n-type (in contrast to silicon doping) but with carrier concentrations dependent on growth conditions. We have used secondary ion mass spectrometry (SIMS) measurements to confirm the concentration of tin incorporated and its distribution within the layers.

In-situ second-harmonic generation study of the molecular beam epitaxy growth of GaAs

In-situ second-harmonic generation study of the molecular beam epitaxy growth of GaAs

Tin as an n-type dopant in the molecular beam epitaxial growth of GaAs(111)A

We have made a systematic study of the tin doping of GaAs layers grown on GaAs(111)A substrates using molecular beam epitaxy (MBE). A series of samples were grown with a range of substrate temperatures (from 460 to 620°C), As:Ga flux ratios (5:1 to 25:1) and tin concentrations (10 16 to 10 20 atoms cm −3). Layers grown on (111)A surfaces were n-type (in contrast to silicon doping) but with carrier concentrations dependent on growth conditions. We have used secondary ion mass spectrometry (SIMS) measurements to confirm the concentration of tin incorporated and its distribution within the layers.

In-situ second-harmonic generation study of the molecular beam epitaxy growth of GaAs

We report on the first observation of surface second-harmonic generation (SHG) during the molecular beam epitaxy (MBE) growth of GaAs homoepitaxy on a GaAs(100) substrate. We used a specific optical arrangement which enabled us to observe the surface SHG and the reflection high-energy electron diffraction (RHEED) pattern simultaneously. We found that the surface SH intensity increased according to a change from an As-stabilized to a Ga-stabilized surface due to an interruption of the As flux while keeping the Ga flux constant. We show that the surface SH intensity has its maximum value when there is about 1 monolayer (ML) of excess Ga on the surface.

Frequency analysis of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on nominally oriented (111)B substrates

Frequency analysis of reflection high-energy electron diffraction (RHEED) intensity oscillations during GaAs growth by molecular beam epitaxy on nominally-oriented (111)B substrates is reported. Double frequency oscillations have been observed and analyzed in a wide range of substrate temperatures. Because the growth rate deduced from RHEED frequency analysis was found to be independent of substrate temperature, no Ga loss from the sample surface seems to take place during growth under conditions which allow RHEED intensity oscillations.

TMGa /TEGa interactions in metalorganic molecular beam epitaxy

Using TMGa and TEGa simultaneously for the metalorganic molecular beam epitaxy growth of GaAs, interactions between the precursors have been observed. Whereas the resulting growth rate is unaffected, the obtained carrier concentrations reveal deviations up to 85% from the superpositioned values. Separate and common injection of both group III alkyls have been investigated. From these, interactions within the common group III injector, if they take place at all, are found to be negligible compared to interactions on the surface.

Chemical beam epitaxial growth of GaAs from tertiarybutylarsine and triethylgallium precursors

Triethylgallium and precracked tertiarybutylarsine (TBAs) were used as precursors for the chemical beam epitaxial growth of GaAs. The main decomposition products of TBAs are AsH free radicals, AsH 3, isobutane and isobutene. Growth rates up to 0.68 monolayers s −1 were obtained. All the grown layers show p-type conductivity with a background acceptor concentration in the mid 10 16 cm −3 range with a compensation ratio of about 0.3. Photoluminescence spectra show that carbon is the main acceptor impurity.

Surface diffusion processes in molecular beam epitaxial growth of GaAs and AlAs as studied on GaAs (001)-(111)B facet structures

Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)B and (001) depend strongly on the As flux and are mainly determined by the diffusion of Ga ad-atoms between the two planes. In contrast, the diffusion of Al is found to be almost negligible, irrespective of the As flux. By analyzing the shape of the facet, the diffusion length, λ, of Ga on a (001) surface is estimated to be about 1 μm at 580 °C, while that of Al is about 0.02 μm. On (111)B, λ of Ga is found to be several μms. The reflectivity of diffusing Ga atoms is found to be far less than 1 for the (001)-(111)B boundary, and almost unity at facet boundaries where the (111)B side surfaces are bound by the (11̄0) side walls.

Two-dimensional arsenic precipitation by In delta doping during low temperature molecular beam epitaxy growth of GaAs or AlGaAs

Low temperature (LT) GaAs delta doped with In and Al have been grown by molecular beam epitaxy and annealed at 600–900 °C for 10 min. As precipitates have been observed to form preferentially on In doping planes while depleting on the Al planes. Similar As precipitates in In-doped LT-Al0.25Ga0.75As are 50% more efficient than that of GaAs. The accumulation or depletion of As precipitates in two-dimensional planes in LT materials using isoelectronic impurities show that the phenomena is not directly related to the electronic properties of dopant impurities and therefore has many device applications.

Molecular beam epitaxial growth of GaAs on CaF2/Si(111) substrate

In this work, molecular beam epitaxial (MBE) growth of GaAs on CaF2/Si(111) substrates has been studied with both Rutherford backscattering spectroscopy and transmission electron microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer improves the Ga wettability on the CaF2 surface and, if properly controlled, leads to two-dimensional (2D) nucleation of GaAs on the CaF2/Si(111) surface as opposed to the more commonly observed three-dimensional growth. In subsequent growth, two kinds of twins have been observed. All samples were observed to have microtwins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000 Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D mode at lower temperature, or, it will suffer from the formation of big rotational twins at higher temperature. It has been observed that growth on the vicinal substrates tilted to [1̄1̄2] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window.

The role of excess arsenic during the metalorganic molecular beam epitaxial growth of GaAs from trimethylgallium and As 2

The availability of active arsenic sites for the decomposition of trimethylgallium (TMGa) during the MOMBE (metalorganic molecular beam epitaxy) growth of GaAs using As 2 has been investigated using RHEED (reflection high electron energy diffraction) intensity oscillations. Changes in the oscillation period are observed at low effective V/III flux ratios at substrate temperatures between 500 and 580°C. The period immediately following the initiation of growth is shorter than the period in the latter part when steady state is achieved. These results indicate that the TMGa decomposition efficiency is strongly affected by the surface chemistry induced by excess arsenic.

Metalorganic molecular beam epitaxy growth of GaAs on patterned GaAs substrates

GaAs layers were grown on etch-patterned (100) GaAs substrates by MOMBE (metalorganic molecular beam epitaxy) using TEGa (triethylgallium) and thermally cracked TEAs (triethylarsine). Morphology and orientation dependencies of the grown facets on the growth temperature (400–630°C) and V/III ratio (2–4) are investigated. Good morphology of grown layers was obtained on (111)A side facets at a low V/III ratio of 3 and low growth temperatures of 450–500°C. We also found strong evidence that the formation of facets is not only governed by the migration of Ga precursors and/or Ga atoms, but also by a preferential catalytic decomposition of Ga precursors on the facet edges.