Atsutoshi Doi

Stepwise monolayer growth of GaAs by switched laser metalorganic vapor phase epitaxy

Growth of GaAs by repeated deposition of single atomic layers using the switched laser metalorganic vapor phase epitaxy technique is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for stepwise epitaxy—the ideal atomic layer epitaxy. This is achieved by suppressing pyrolytic decomposition and favoring photocatalytic decomposition of trimethylgallium (TMG). A growth model for stepwise monolayer epitaxy is proposed which suggests that photocatalytic decomposition of TMG occurs only at surface As atoms and not at Ga atoms.Growth of GaAs by repeated deposition of single atomic layers using the switched laser metalorganic vapor phase epitaxy technique is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for stepwise epitaxy—the ideal atomic layer epitaxy. This is achieved by suppressing pyrolytic decomposition and favoring photocatalytic decomposition of trimethylgallium (TMG). A growth model for stepwise monolayer epitaxy is proposed which suggests that photocatalytic decomposition of TMG occurs only at surface As atoms and not at Ga atoms.

Atomic‐layer growth of GaAs by modulated‐continuous‐wave laser metal‐organic vapor‐phase epitaxy

Atomic‐layer epitaxy (ALE) including self‐arresting deposition mechanism at 100% surface coverage is realized in GaAs by a modulated‐continuous‐wave laser metal‐organic vapor‐phase epitaxy technique. Selective decomposition of trimethylgallium (TMG) or triethylgallium (TEG) on an As‐atom layer by laser irradiation is an important mechanism to realize the ALE. The experimental results are well‐explained by a calculation based on this selective decomposition mechanism.

Laser enhanced metalorganic chemical vapor deposition crystal growth in GaAs

An enhanced crystal growth of GaAs is observed in metalorganic chemical vapor deposition (MOCVD) under laser illumination. It is difficult to understand this enhancement effect only by a pyrolitic effect and we should consider photochemical processes like photoassisted catalytic or surface effect. This laser enhancement makes patterned crystal growth in MOCVD possible.

Growth of GaAs by switched laser metalorganic vapor phase epitaxy

Crystal growth of GaAs by switched laser metalorganic vapor phase epitaxy (SL MOVPE) is reported. This growth technique is achieved by combining laser MOVPE and atomic layer epitaxy. The growth process in SL MOVPE can be explained by a model which assumes that trimethylgallium adsorbed on the crystal surface is decomposed in a photocatalytic reaction and that the decomposition rate depends on the surface species present on the substrate.

Characteristics of laser metalorganic vapor‐phase epitaxy in GaAs

Growth characteristics of a laser metalorganic vapor‐phase epitaxy (laser MOVPE) and the electrical and optical properties of the epitaxial layer grown by the technique are examined. The growth rate under laser MOVPE decreases with increasing substrate temperature in contrast with conventional MOVPE. The growth rate also depends on the type of the substrate, total gas flow rate and the incident laser power. The mechanism of laser MOVPE seems not to be a photothermal effect but a surface photochemical effect. The intensity of the photoluminescence at room temperature for the epitaxial layer grown by the laser MOVPE is found to be stroger than that of the epitaxial layer grown without the laser irradiation under the same growth condition. The carrier concentration is also found to be modified by the laser irradiation. It is emphasized that the laser MOVPE is very useful as a new crystal growth technology.

A Growth Analysis for Metalorganic Vapor Phase Epitaxy of GaAs

Metalorganic vapor phase epitaxy (MOVPE) of GaAs is analyzed using a new growth model. Surface reactions for trimethylgallium or triethylgallium adsorbed on the substrate surfaces are assumed to be the growth-rate-limiting steps. A catalytic effect is taken into account by assuming different decomposition rates for adsorbed alkyls on Ga- and As-terminated surfaces. The surface reactions are expressed in terms of reaction times and analyzed using a rate equation approach. Parameters in a rate equation are determined by fitting to the experimental results obtained by various methods: conventional MOVPE with and without laser irradiation, pulsed MOVPE, and laser atomic layer epitaxy. Good agreement between experiments and calculations in all growth methods shows the usefulness of the model.

Improvement of Crystal Composition in Ga1-xAlxAs LPE Layers Grown under Conditions of Constant Cooling Rate

Liquid phase epitaxy of Ga1-xAlxAs under conditions of a constant cooling rate are analyzed by making use of a diffusion limited growth model. The influence of growth conditions on the AlAs mole fraction in the epitaxial layer as well as the epitaxial layer thickness are investigated in detail. It is shown that the uniform AlAs mole fraction can be obtained by selecting appropriate growth conditions: the cooling rate, solution thickness, and initial supercooling. It is also shown that the dependences of the layer thickness on growth conditions are similar to those of GaAs except for a factor that depends on the AlAs mole fraction.

ENHANCED DIFFUSION IN ION-IMPLANTED SILICON.

Abstract Concentration profiles of 20 keV ion implanted antimony into silicon single crystals are measured by radio-activation analysis and the enhanced diffusion of antimony is observed. The concentration profiles and the diffusion coefficient of antimony are found to be independent of temperature over the range between 500 and 800°C during ion implantation. The enhancement of diffusion during annealing after room temperature ion implantation is the same as that during high temperature ion implantation. The diffusion coefficient is estimated to be 1.1 × 10−15 cm2/sec for diffusion during high temperature ion implantation and that during annealing after room temperature ion implantation. The measured concentration profiles agree very well with the calculated concentration profiles. These results are explained on the basis of a vacancy mechanism.

Laser-assisted atomic layer epitaxy

Abstract Laser-assisted atomic layer epitaxy (laser ALE) is reviewed. The characteristics and the mechanism of laser ALE are discussed, with a brief description of possible applications. The mechanism of laser ALE seems to be atom-selective decomposition of trimethylgallium and triethylgallium at the surface of GaAs. This atom-selective decomposition is not a thermal effect but a photochemical effect on the GaAs surface.

Maskless Fabrication of High Quality DFB Laser Gratings by Laser Induced Chemical Etching

High quality submicron DFB laser gratings with 130 nm groove depth are fabricated without roughness on a grating surface by laser induced chemical etching. It is found that rigid configuration of an irradiation cell and directional etching performance of laser etching is very important to obtain high quality gratings.