Yoshitaka Morishita

Surface diffusion length of Ga adatoms on (1̄1̄1̄)B surfaces during molecular beam epitaxy

The spatial variation of the growth rate on mesa‐etched GaAs (111)B substrates during molecular beam epitaxy of GaAs is measured from the period of the reflection high‐energy electron diffraction (RHEED) intensity oscillation using in situ scanning microprobe RHEED. The surface diffusion length of Ga adatoms on the (111)B surface is determined from the spatial variation of the growth rate. The surface diffusion length on the (111)B surface increases as the substrate temperature is raised or the arsenic pressure is decreased. The typical value of the diffusion length is about 10 μm at a substrate temperature of 580 °C and an arsenic pressure of 5.7×10−4 Pa, which is an order of magnitude larger than that on the (100) surface along the [011] direction. The activation energy of the surface diffusion length changes with the surface reconstruction. Anisotropic diffusion, as reported for the (100) surface, is not observed on the (111)B surface.

Substrate-Orientation Dependence on Structure and Magnetic Properties of MnAs Epitaxial Layers

Ferromagnetic MnAs layers were grown on (001), (111)A, and (111)B GaAs substrates by molecular-beam epitaxy at substrate temperatures (T s) in the range from 150 to 400° C. The crystal structure of the MnAs was NiAs type and its orientation was found to change depending on the substrate, (1101) for the (001) GaAs substrate and (0001) for the (111)A and (111)B substrates at T s between 300 and 400° C. Polar magneto-optical Kerr-effect measurement demonstrated a crystal-orientation dependence of Kerr rotation and Kerr ellipticity spectra of the MnAs epitaxial layers.

Gas source MBE growth of InP

We report the electrical and optical properties of InP epilayers grown by gas source molecular beam epitaxy (GSMBE) using trimethylindium (TMI) and phosphine (PH3) under various growth conditions. Reflection high-energy electron diffraction (RHEED) intensity oscillations during the growth of InP are also described. It is found that high quality epilayers are obtained at about 490°C, and at this temperature the RHEED intensity oscillations with periods of more than 700 are observed.

Observations on intensity oscillations in reflection high‐energy electron diffraction during gas source molecular beam epitaxy of InP

We report the first observation of reflection high‐energy electron diffraction intensity oscillations during the growth of InP using trimethylindium and phosphine in gas source molecular beam epitaxy (GSMBE). By optimizing the growth conditions, intensity oscillations more than 700 periods have been observed. The temperature and flux dependence of the oscillating behavior have been studied. Results indicate that the growth of InP by GSMBE is predominantly via a two‐dimensional layer‐by‐layer mode.

Lateral growth of GaAs on patterned {1¯1¯1¯}B substrates for the fabrication of nano wires using metalorganic molecular beam epitaxy

We have grown GaAs nano wire structures (45 × 20 nm2) buried in AIAs layers by lateral metalorganic molecular beam epitaxy on the terraced sidewalls of mesa-grooved (-1-1-1)B substrates. The growth of GaAs occurred primarily on the sidewall of the mesa-grooves and not on the (-1-1-1)B surface for arsenic pressures greater than 2.0 × 10−3 Pa at a substrate temperature of 480°C. An (0-1-1) facet formation during the lateral epitaxy at the intersection region between the bottom (-1-1-1)B surface and the (1-2-2)A sidewall has been directly observed by real-time scanning microprobe reflection high-energy electron diffraction. The growth rate on the (0111) facet was estimated from the variation of its width with growth time.

Effect of hydrogen molecules on growth rates of GaAs in gas source molecular beam epitaxy

We observed intensity oscillations of reflection high-energy electron diffraction during growth of GaAs using triethylgallium (TEG) and arsine (AsH3). The oscillation period increased with increasing AsH3 flow rate. We found that introduction of H2 or N2 during the growth also caused a decrease in the growth rate. The growth rate reduction is explained by assuming that transient residence of H2 or N2 molecules on the growing surface impedes adsorption of TEG molecules.

Surface diffusion lenght during MOMBE and CBE growth measured by μ-RHEED

The growth rates of layers grown on a mesa-etched (001) GaAs surface were measured by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED) from the period of the RHEED intensity oscillation in real time. The diffusion lenght of the surface adatoms of column III elements was determined from the gradient of the variation of the growth rates in the cases of MBE, MOMBE using trimethylgallium (TMGa) and CBE using TMGa or triethylgallium (TEGa) and arsine (AsH3). The obtained values of the diffusion lengths were of the order of a micrometer in every case of the source-material combination. In the case of metalorganic materials as Ga source, it was found that the diffusion length was larger than that of Ga atom from metal Ga source. Since the substrate temperature of the present experiment is high enough to decompose TMGa and TEGa on the surface, Ga adatoms are considered to be responsible to the surface diffusion. Therefore, it is considered that the derivatives of the metalorganic molecules such as methyl radicals affect the diffusion of Ga adatoms.

Surface diffusion length during MBE and MOMBE measured from distribution of growth rates

Resumen Optoelectronics Technology Research Laboratory, 5-5 Tohkodai, Tsukuba, Ibaraki 300-26, Japan

Lateral Metalorganic Molecular Beam Epitaxy of GaAs on Patterned (1̄1̄1̄)B Substrates

GaAs layers were grown on patterned ()B substrates having ()A sidewalls with various arsenic fluxes at a fixed temperature of 480°C by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMGa) and metal arsenic. Vertical growth rate on the top and bottom ()B surfaces decreased rapidly as the arsenic flux was increased. For arsenic fluxes of 2.0×10-3 Pa and more, only lateral epitaxy on the ()A sidewall was achieved. Real-time scanning microprobe reflection high-energy electron diffraction (µ-RHEED) observations showed that the surface smoothness of the epitaxial layer was maintained throughout the growth time under the optimized condition.

Molecular beam epitaxy of GaAs x P 1 - x using low-energy P + ion beam

We describe the epitaxial growth of GaAsxP1-x (0 <x < 0.7) on GaAs(00l) substrates using mass-separated low-energy P+ ions, and Ga and As4 molecular beams. Epilayers have been obtained at growth temperatures(Tg) ranging from 300 to 650° C at P+ ion energies(Ep+) between 50 and 300 eV. We have investigated the growth rate as a function ofEp+, and the film composition as a function of the flux ratio of As4 to P+,Tg andEp+. The sticking coefficient of phosphorus is markedly enhanced by using P+ ion, compared with that of As4. As the flux ratio of As4 to P+ is increased from 0 to 8, the composition ratiox of GaAsxP1-xfilms varies from 0 to 0.5. The composition ratiox decreases slightly with increasingTg from 400 to 650° C, and increases with increasingEp+. Film surfaces are smooth atEp+ below 100 eV, and their morphology is degraded with increasing energy.