Y. Morishita

Effect of hydrogen on the surface‐diffusion length of Ga adatoms during molecular‐beam epitaxy

Systematic measurements were carried out on the surface‐diffusion length of Ga adatoms during the molecular‐beam epitaxy of GaAs in the presence of hydrogen atoms (H⋅) or hydrogen molecules (H2). The spatial variation of the growth rate on the (100) surface adjacent to the (111)A surface was measured from the period of the reflection high‐energy electron diffraction (RHEED) intensity oscillations using in situ scanning microprobe RHEED. The surface‐diffusion length of Ga adatoms, which was derived from the spatial variation of the growth rate, becomes larger along with an increase in the H⋅ or H2 pressure. It also increases as the substrate temperature is raised under H⋅ or H2 pressure. The diffusion length in the case of H⋅ introduction is larger than that in the case of H2 introduction.

Effects of atomic-hydrogen assistance on hot-wall epitaxy growth of MnSbGaAs heterostructures

Prominent improvement of surface flatness was observed in MnSb films prepared by atomic-hydrogen assisted hot wall epitaxy technique on GaAs substrate. The effect is discussed in terms of surfactant effect of atomic hydrogen.

Self-Organized Formation of Hexagonal Hollow Arrays in Anodic GaAs

The dependence of the structural properties on the anodization conditions was investigated to gain insights into the formation conditions of ordered hollow arrays on GaAs surfaces. The microscopic surface features were observed by a secondary electron microscope. Honeycomb hollows were formed on the substrate surfaces anodized with an appropriate bias voltage between the substrate and the platinum electrode under the illumination of W lamp. Ordered hexagonal hollows with the average diameter and standard distribution of 200 and 19 nm were obtained for the sample prepared by the anodization with the bias voltage of 12 V under the illumination of W lamp in an NH4OH solution (29 wt%) at 0°C.

Effects of regularity of honeycomb hollows formed by the anodization of GaAs substrates on the molecular-beam epitaxial growth of InAs dots

InAs dots were grown by molecular-beam epitaxy on honeycomb hollows formed by anodization of GaAs substrates. It was found that InAs dots were selectively grown at the bottom of honeycomb hollows formed by anodization of GaAs substrates in an NH 4 OH solution. The average size of InAs dots and its coefficient of variation on anodized substrates were considerably affected by the regularity of hollows. In the case of the growth on a high-ordered hollow array, the average diameter (37.4 nm) and standard deviation (15.3 nm) were comparable to those obtained for InAs dots grown on an unpatterned substrate. On the other hand, in the case of the growth on a low-ordered hollow array, the average diameter (48.0 nm) and standard deviation (19.4 nm) were about 30% larger than those obtained for InAs dots grown on an unpatterned substrate.

Real‐time scanning microprobe reflection high‐energy electron diffraction observations of InGaAs surfaces during molecular‐beam epitaxy on InP substrates

The microscopic surface features were observed during the molecular‐beam epitaxy of InxGa1−xAs on InP (100) substrates by scanning microprobe reflection high‐energy diffraction in real time as a function of x from 0.41 to 0.96. In the case of In0.41Ga0.59As (the lattice mismatch of the strained layer was f=−0.77%, where the minus sign represents a smaller lattice constant of an epitaxial layer than that of a substrate), three‐dimensional island growth was observed from the start of growth. On the other hand, two‐dimensional layer‐by‐layer growth was maintained during growth of InxGa1−xAs with x=0.45–0.75 (f=−0.47 to +1.48%, where the plus sign represents a larger lattice constant of an epilayer than that of a substrate). While the growth of compressive epilayers with f between +0.36% and +1.48% proceeded, a surface crosshatched morphology was observed after the growth of certain film thicknesses, which were dependent on the lattice mismatch. A rough textured morphology was observed instead of a crosshatch...

Effects of Growth Interruption during Growth of InAs Wetting Layer on Formation of InAs Quantum Dots

The effects of growth interruption on the formation of InAs quantum dots (QDs) grown on GaAs substrates by molecular beam epitaxy were investigated. The growth interruption was carried out during the growth of InAs with a nominal thickness of 1.2 monolayers (ML). The number of growth interruptions was varied between 1 and 6, and the interruption time (tINT) was varied between 5 and 15 s. After the growth interruption, a 2.8-ML-thick InAs was grown, and the total thickness was nominally 4 ML. The structural characterization was performed using an atomic force microscope. In the case of the growth with tINT=5 s, the average size of QDs decreased and their density increased with increasing number of growth interruptions. On the other hand, the size of QDs increased and their density decreased with increasing number of growth interruptions for the growth with tINT=10 or 15 s. These results suggested that the extremely uniform distribution of In adatoms in the wetting layer due to the migration of In atoms on the surface as well as the reduction of stress in the wetting layer due to the interchange of In and Ga atoms during the growth interruption affect the size and density of QDs.

Influence of hydrogen radicals on the reduction of carbon incorporation into chemical beam epitaxial GaAs

Abstract In order to investigate the influence of hydrogen radicals (H·) on carbon incorporation into chemical-beam epitaxial GaAs, H· generated by flowing H 2 through a hot tungsten filament was intentionally introduced into a trimethylgallium (TMGa)-AsH 3 (cracked at 850°C) and a TMGa (or metal Ga)-trisdimethylaminoarsine (TDMAAs) system. In the case of the TMGa-AsH 3 -H· system, the residual carbon concentrations, measured by secondary ion mass spectrometry, in epitaxial layers grown at 490°C rapidly decreased along with an increase in the H 2 flow rate in a low-flow region, and saturated at around 1 × 10 18 cm -3 in a higher flow region. On the other hand, carbon incorporation (6 × 10 17 cm -3 at 490°C) in TMGa-TDMAAs was less than that in TMGa-AsH 3 . Since no residual carbon over the detection limit ((1−2) × 10 17 cm -3 ) was detected in metal Ga-TDMAAs, the carbon in TMGa-TDMAAs was clarified as having been derived from TMGa. However, the introduction of H· did not reduce the carbon incorporation in TMGa-TDMAAs. Influence of injected H· on the carbon reduction is discussed in relation to the adsorption of uncracked H 2 and surface species derived from TDMAAs on a growing surface.

Molecular-beam epitaxy of InAs on anodized GaAs substrates

InAs dots were grown on anodized (001) GaAs substrates by molecular-beam epitaxy. It was found that InAs dots were selectively grown at the bottom of beehive-like etch-pits formed by anodization of GaAs substrates in an NH 4 OH solution. The average size of InAs dots and its coefficient of variation on anodized substrates was larger than that on unpatterned substrates at the total amount of deposited In atoms less than about 4.0 ML, and vice versa at the deposited In amount of 10 ML. In the case of 10.0-ML InAs growth, one or two dots were grown at a bottom of beehive-like etch-pits on the anodized substrates, and the average size of InAs dots and its coefficient of variation on the anodized substrate were about two-third times smaller than those on the unpatterned substrate.

Real-Time Observations on the Cleaning Process of Patterned GaAs Substrates.

We report on real-time scanning microprobe reflection high-energy electron diffraction (µ-RHEED) observations on the cleaning process of mesa-etched GaAs (100) surfaces for the first time. Both the initial (100) surfaces and the (111)A sidewall have been found to be uniformly cleaned at temperatures of about 400° C using atomic hydrogen ( H•); further, RHEED intensity oscillations more than 50 periods have been observed during direct molecular-beam epitaxy (without a GaAs buffer layer) of GaAs on the cleaned (100) surface. On the other hand, an inhomogeneous desorption of the oxide layer has been observed during conventional thermal cleaning under an As4 pressure at about 600° C. The results indicate that the H• treatment of patterned substrates is useful for obtaining smooth and clean surfaces without the growth of a GaAs buffer layer.

Magneto-optical spectra in MnSb and MnAs films prepared by atomic-hydrogen assisted hot wall epitaxy on GaAs

Thin films of NiAs-type MnSb and MnAs were epitaxially grown on GaAs (1 0 0) and (1 1 1) substrates by an atomic-hydrogen assisted hot-wall technique. Polar magneto-optical spectra were measured between 1.2 and 6 eV. Crystal-orientation dependence of the spectra were clearly observed.