Akihiko Yoshikawa

Atomic layer epitaxy of ZnS by a new gas supplying system in low-pressure metalorganic vapor phase epitaxy

Atomic layer epitaxy (ALE) for ZnS has been investigated by low-pressure metalorganic vapor phase epitaxy (MOVPE) using dimethyl zinc (DMZn) and H2S as reactants. A new gas supplying system was developed for the ALE growth of ZnS. By optimizing the purge conditions, ALE growth of ZnS on glass substrate can be achieved over a wide temperature range.

Ar Ion Laser-Assisted MOVPE of ZnSe Using DMZn and DMSe as Reactants

Growth of ZnSe layers by Ar ion laser-assisted MOVPE using DMZn and DMSe has been investigated. It is shown that an Ar ion laser can be a useful light source for the photoassisted MOVPE of ZnSe. By utilizing several Ar ion laser emission lines near the absorption edge of ZnSe as the irradiation light, it has been reconfirmed that the absorption of photons by the ZnSe layer is essential for the growth rate enhancement in the photoassisted MOVPE of ZnSe. Furthermore, it has been found for the first time that hydrogen gas plays a very important role in the reaction between DMZn and DMSe to form ZnSe under photoirradiation.

Effects of Ar ion laser irradiation on MOVPE of ZnSe using DMZn and DMSe as reactants

Abstract The growth mechanism in photoassisted MOVPE of ZnSe on GaAs using DMZn and DMSe has been investigated by using an Ar ion laser as an irradiation source. It has been reconfirmed that photons with higher energies that the band gap of ZnSe at the growth temperature can contribute to a growth rate enhancement. Furthermore, it has been found that the presence of a growing ZnSe layer itself greatly affects the following film growth, that is, (1) the growth rate dramatically increases with increasing thickness of the predeposited ZnSe layer and (2) it also reflects the crystallinity of the predeposited layer. From these results, a plausible growth model utilizing a band diagram of a ZnSe/GaAs junction has been proposed, in which excess holes photoinduced in the ZnSe layer play an important role in the growth rate enhancement at the ZnSe surface.

Controlled conductivity in iodine‐doped ZnSe films grown by metalorganic vapor‐phase epitaxy

Iodine‐doped ZnSe films have been grown on GaAs by low‐pressure metalorganic vapor‐phase epitaxy using dimethylzinc and hydrogen selenide as reactants. In order to accomplish an accurate control of the carrier concentration in the films over a wide range, ethyliodide diluted to 1000 ppm was used as a dopant source. It has been shown that the carrier concentration can be changed in the range from 1015 to 1019 cm−3 by varying the flow rate of ethyliodide. Furthermore, the films with carrier concentrations below 1018 cm−3 exhibit strong blue emission with suppressed deep level emissions. The origin of blue emission has been ascribed to the iodine donors incorporated during growth. According to the results shown, it has been concluded that iodine is a superior donor dopant for ZnSe from a standpoint of the controllability and reproducibility of electrical and photoluminescence properties of the n‐type films over a wide range.

“MBE-Like” and “CVD-like” atomic layer epitaxy of ZnSe in mombe system

Abstract Atomic layer epitaxy (ALE) of ZnSe films has been examined by MOMBE system using DMZn and H 2 Se as source materials. Depending on whether the source materials are cracked before reaching substrate or not, ALE of ZnSe by both “MBE-like” and “CVD-like” modes can be achieved. In “MBE-like” ALE mode, since thesource materials are supplied onto the subsrate surface in the form of constituent elements, they can migrate on the surface through fairly long distance. On the other hand, in “CVD-like” ALE mode, DMZn and H 2 Se themselves react to form ZnSe on the surface, it is fairly hard for them to migrate on the surface. It has been found that “MBE-like” ALE mode is superior to “CVD-like” ALE mode in terms of photoluminescence properties and surface morphology.

On the mechanism of growth-rate enhancement by photocatalysis in metalorganic vapor phase epitaxy of ZnSe

Abstract The growth and/or reaction mechanism of photoassisted MOVPE of ZnSe using DMZn and DMSe has been studied. Some evidence is shown which indicates that the dissociation of Se sources, i.e., DMSe of H2Se, may be initiated by the effect of photoinduced excess holes at the ZnSe surface, and this is the rate-limiting reaction for the growth rate enhancement under photo-irradiation. Furthermore, a brief discussion is provided concerning how the excess holes contribute to the dissociation of these Se sources at the surface. Some plausible reaction models will be proposed.

A study of growth mechanism of ZnS and ZnSe in MOMBE using dimethylzinc and chalcogen hydrides as reactants

Abstract ZnS and ZnSe films have been grown by MOMBE using dimethylzinc, H 2 S and H 2 Se as reactants. The growth mechanism of these films has been studied by investigating the effects of the source-gas cracking on film growth rate. It has been found that the cracking of the source gases drastically affected the growth kinetics and surface morphology of the ZnS and ZnSe films. A speculative model is offered of the reactions among precursors on the substrate surface. A quite smooth and featureless surface can be achieved when both dimethylzinc and chalcogen hydrides are cracked. In contrast, when the source gases are not cracked, premature reaction on the substrate surface takes place, resulting in a rough surface.

Growth of Lattice-Matched ZnSe-ZnS Superlattices onto GaAs Substrates by Metalorganic Molecular Beam Epitaxy

This paper describes the results of the first attempt to reduce misfit dislocations in epilayers of a wide-band-gap II-VI semiconductor on GaAs substrates by utilizing the ZnSe-ZnS strained-layer superlattice (SLS) structure. From a theoretical calculation, SLSs consisting of a 200 A-ZnSe and a 10 A-ZnS layer in one period can be grown as lattice-matched SLSs to GaAs. It has been found from the photoluminescence measurements and electron-beam-induced current (EBIC) image observations that the generation of misfit dislocations can be markedly reduced, as expected.

Effects of Substrate Materials and Their Properties on Photoassisted Metalorganic Vapor Phase Epitaxy of ZnSe

Effects of substrate materials and their properties on photoassisted MOVPE of ZnSe using DMZn and DMSe as reactants have been investigated. For GaAs substrates, the presence of a thin predeposited ZnSe buffer layer and its quality greatly affect the subsequent film growth. However, for InP substrates, no essential effect of the buffer layer has been observed. Furthermore, in both substrates, the conduction type makes no significant difference to the results of photoassisted MOVPE. These results can be interpreted by a proposed growth model in which photoinduced excess holes in the ZnSe layer contribute to the film growth.

Use of dimethyl hydrazine as a new acceptor-dopant source in metalorganic vapor phase epitaxy of ZnSe

Abstract Use of dimethyl hydrazine (DMHz) as a new dopant source for nitrogen in metalorganic vapor phase epitaxy (MOVPE) of ZnSe has been investigated. It is shown that DMHz can be a promising alternative to ammonia as a dopant source for nitrogen in MOVPE of ZnSe. That is, because of a remarkable ease of pyrolysis of DMHz compared with ammonia, nitrogen can be efficiency incorporated into the ZnSe films by using DMHz. Furthermore, it is shown that the incorporation rate of nitrogen into the films drastically decreases with substrate temperature in both cases using DMHz and ammonia, though this tendency is weak in the case of DMHz compared with ammonia.