Mitsuo Kawabe

Low-Temperature Cleaning of GaAs Substrate by Atomic Hydrogen Irradiation

Low-temperature cleaning of GaAs substrate by atomic hydrogen irradiation has been demonstrated. Atomic hydrogen was provided by dissociation of hydrogen gas, which was carried out in a simple cracking cell with a 1500°C tungsten filament. Auger electron spectroscopy showed that carbon was removed at 200°C and oxygen was removed at 400°C by 30-min atomic hydrogen irradiation. The surface cleaning of GaAs was confirmed by the change of RHEED pattern from halo to streak after the hydrogen irradiation.

Self-annihilation of antiphase boundary in GaAs on Si(100) grown by molecular beam epitaxy

It has been shown that single domain GaAs can be grown on Si(100) which consists of two domains. A mechanism for self-annihilation of the antiphase boundary in the process of GaAs growth has been proposed to explain the experimental result.

Effects of Be and Si on disordering of the AlAs/GaAs superlattice

Effects of Be doping and the interaction of Be and Si on the disordering of 15‐nm AlAs/15‐nm GaAs superlattices were studied. Be doping of more than 4×1019 cm−3 causes the intermixing of Al and Ga during epitaxial growth and the effect of Be surface accumulation is observed at the growth temperature of 540 °C, while after incorporation of Be in the crystal the annealing of 750 °C, 2 h does not cause any remarkable change in the superlattice structure. Be doping in the Si‐doped superlattice shows remarkable suppression of the disordering of superlattice when the Be doping level exceeds that of Si.

Highly packed InGaAs quantum dots on GaAs(311)B

We have fabricated highly packed and ordered In0.4Ga0.6As quantum dots (QDs) array on GaAs(311)B substrate without coalescence of QDs. Reflection high-energy electron diffraction and Auger spectra suggest the inhomogeneous distribution of In and Ga in QD. In concentration near the surface of QD is larger than that of the inside, and the inhomogeneous distribution of In and Ga in QDs prevents QDs from merging.

Disordering of Si-Doped AlAs/GaAs Superlattice by Annealing

Effect of Si-doping levels and annealing temperature on disordering of 150-A AlAs/150-A GaAs superlattices is studied. The doping level of 4×1018 cm-3 cause disorder for 800°C, 2 h annealing, while the doping level of 1×1018 cm-3 does not induce disorder on this annealing condition. A superlattice which is doped with 1×1019 Si cm-3 disintegrates after 650°C, 2 h annealing and the diffusion coefficient of Al–Ga interdiffusion is estimated to be 3×10-17 cm2s-1. For 800°C, 2 h annealing the two undoped AlAs/GaAs layers adjacent to the doped region are disordered by Si diffusion.

Initial Stage and Domain Structure of GaAs Grown on Si(100) by Molecular Beam Epitaxy

The initial stage of GaAs epitaxial growth on Si(100) has been studied by RHEED and AES. On exposure to a As4 flux, the Si surface is covered with one or two monolayers of As which are stable up to 700°C, while Ga on Si desorbs even at 500°C. There are two kinds of Si-As reconstruction, which depend on the temperature of Si exposed to As4 flux. One is 1×2 for high temperature (>600°C) and the other is 2×1 for low temperature (<450°C) when the Si substrate has 2×1 reconstruction. The surface reconstructions of GaAs grown on Si(100)-As 1×2 and Si(100)-As 2×1 are perpendicular to each other, which indicates that the domain direction of GaAs to Si substrate is different depending on the initial growth temperature.

Growth modes in atomic hydrogen‐assisted molecular beam epitaxy of GaAs

It has been shown that irradiation with atomic hydrogen during the growth of GaAs in molecular beam epitaxy (MBE) promotes an ideal layer‐by‐layer two‐dimensional nucleation and step‐flow growth mode on GaAs(001) substrates, thereby resulting in atomically flat surfaces. Fundamentally important observations related to elementary processes have been presented based on the reflection high‐energy electron diffraction (RHEED) and atomic force microscopy (AFM) measurements. A growth model for the atomic hydrogen‐assisted GaAs MBE has been postulated.

Basic mechanisms of an atomic force microscope tip-induced nano-oxidation process of GaAs

An atomic force microscope (AFM) tip-induced direct nano-oxidation process of GaAs(100) substrates has been investigated, and is viewed as a promising method for the fabrication of nanometer-scale electronic devices such as single electron tunneling transistors. The effects of the AFM drawing parameters such as tip bias voltage and writing speed as well as the ambient humidity on the oxide line height and width were explored. The rate of reaction and its dependence on electric field strength and oxide thickness were examined to understand the basic mechanisms involved in the tip-induced oxidation of GaAs. The rate of oxidation/anodization was found to decrease rapidly with oxide film growth, which was explained at the simplest level in terms of a self-limiting influence of decreasing electric field strength.

Low dislocation density GaAs on Si heteroepitaxy with atomic hydrogen irradiation for optoelectronic integration

Basic experimental results obtained for the low‐temperature molecular beam epitaxy with atomic hydrogen have been presented. GaAs films grown at different substrate temperatures have exhibited different values of dislocation densities and the average dislocation density as low as 3×104 cm−2 has been successfully obtained for the films grown at a low‐temperature of 330 °C with atomic hydrogen irradiation. These are among the lowest dislocation values reported to date. The surface cleaning effects and reconstruction of vicinal Si(100) surfaces during the atomic hydrogen irradiation, and also the electrical properties of epitaxial films have been investigated and analyzed. Physics behind the drastic dislocation density reduction has been investigated in detail based on the results of cross‐sectional and plan‐view transmission electron microscope observations and analysis of the growth kinetics.

Cracking Efficiency of Hydrogen with Tungsten Filament in Molecular Beam Epitaxy

Atomic hydrogen is known to exert various important effects on the growth of semiconductors in molecular beam epitaxy (MBE). In this work, the cracking efficiencies of hydrogen molecules into atomic hydrogen with a hot tungsten (W) filament have been experimentally determined. Hydrogen atoms recombine at the surface of a heated platinum detector to form molecules releasing the heat of reaction, which results in a temperature increase of the platinum detector, and the cracking efficiencies of atomic hydrogen can be determined by considering the enthalpy of atomization. The cracking efficiency increased exponentially with W filament temperature. At a filament temperature of 1600° C and a H2 gas flow rate of 1.5 ccm for example, the cracking efficiency was determined to be about 1.5% or equivalently, the number of hydrogen atoms resulting from cracking was 2×1016 cm-2s-1 at a H2 pressure of 1.87×10-2 Pa.