Shigeki Yamaga

Electrical and optical properties of donor doped ZnS films grown by low-pressure MOCVD

Abstract The growth and properties of donor impurity doped ZnS films prepared using low-pressure MOCVD have been examined. Trimethylaluminum (TMAl) and hydrogenchloride (HCl) were used as donor dopant sources. With Al doping, ZnS films, with resistivities as low as about 1 Ω cm, can be grown. In the photoluminoscence of Al-doped ZnS, a near-band-edge emission and an SA emission are observed. A correlation between the resistivity and the SA emission intensity was found through which the resistivity decreases with an increase in the SA emission intensity. With Cl doping, films with resistivity as low as 0.2 Ω cm can be grown. It was found, however, that then the HCl flow rate was relatively high, the crystallinity tended to be poor, because of the reaction between HCl and the Zn-source material.

Growth of low-resistivity high-quality ZnSe, ZnS films by low-pressure metalorganic chemical vapour deposition

Abstract Growth of low-resistivity and high-quality ZnSe and ZnS films by low-pressure MOCVD has been examined. It has been shown that ZnSe films having electron mobilities as high as 3650 and 1130 cm2/V·s at 77 K for 3 and 1 μm thick films, respectively, can be obtained. The shallow donor concentration in these films is about 1015-1016 cm-3 and the electron-trap deep-center concentration is less than the shallow donor concentration by a factor of 100. Furthermore, it has been shown for the first time that low-resistivity ZnS films can be grown on GaAs by MOCVD.

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.

Growth of High-Quality ZnSe Films by Low-Pressure Metalorganic Chemical Vapor Deposition

Effects of growth conditions, especially substrate temperature, on the electrical and photoluminescence properties of nominally undoped ZnSe films grown on GaAs substrates by low-pressure MOCVD have been studied. It has been shown that the substrate temperature remarkably affects the electrical and photoluminescence characteristics of films. It was found that high conductivity ZnSe films can be grown without intentional doping, and that high-quality ZnSe films involving low-concentration electron-scattering centers and exhibiting a strong blue near-band-edge emission can be grown.

Growth of Hydrogenated Amorphous Silicon Films by ArF Excimer Laser Photodissociation of Disilane

Hydrogenated amorphous silicon films have been grown on glass substrates by photodissociation of disilane using a pulsed ArF excimer laser foe the first time. Electrical and optical properties of the films have been examined. It was found that the magnitude of the gap energy of laser CVD films is rather large as compared to that of films obtained by a conventional plasma CVD. Preliminary examinations to control the conductivity by impurity doping have also been performed.

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.

Growth and properties of Zn1−xCdxS films on GaAs by low-pressure MOVPE

Abstract Cubic Zn 1− x Cd x S ternary alloy epitaxial films have been grown on (100) GaAs by low-pressure metalorganic vapor phase epitaxy (MOVPE) using dimethyl zinc, dimethyl cadmium and hydrogen sulfide as reactants. The solid composition is shown to be easily controlled over the whole range of composition, although the films tend to be Cd-rich compared with the case of atmospheric pressure MOVPE. It has been found that the solid composition slightly decreases with growth temperature due to the effect of the decrease in the sticking coefficient of cadmium with temperature. The photoluminescence spectra at 18 K of the ternary films are dominated by fairly strong free-to-acceptor emissions. Furthermore, it is shown that low-resistivity ternary films can be grown by iodine doping.

“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.

The dependence on growth temperature of the photoluminescence properties of nitrogen-doped ZnSe grown by MOCVD

Abstract Growth of nitrogen-doped ZnSe films by low pressure MOCVD using dimethylzinc and hydrogenselenide as reactants has been carried out, and the dependence of low-temperature photoluminescence properties of nitrogen-doped films on growth temperature has been examined. It is shown that the nitrogen atoms act as shallow acceptors in ZnSe, with an activation energy of about 100–110 meV. However, some deep centers related to the nitrogen impurity are also introduced into highly nitrogen-doped ZnSe films, and the resistivity of nitrogen-doped ZnSe films remains high.