Kotaro Okamoto

Lateral supply mechanisms in selective metalorganic chemical vapor deposition

Selective epitaxial growth of GaAs was carried out by atmospheric-pressure metalorganic chemical vapor deposition, and lateral supply mechanisms of reactant species from mask areas to window areas were investigated. Since reactant species arriving on SiO2 surfaces were easily reevaporated, deviation from mass balance was observed. In the case of a SiO2 mask with width of more than 20 µm, lateral vapor-phase diffusion dominated over increment of selective epilayers because of short surface-diffusion length on SiO2 surfaces (<1 µm). It was apparent experimentally and analytically that long ridged tails of selective epilayers were formed by lateral vapor-phase diffusion. Appearance of wavelike tails at mask edges was due to surface diffusion from (111)B facets. Surface-diffusion length on (111)B surfaces was estimated at 3 µm.

Selective Epitaxial Growth of GaAs by Metalorganic Chemical Vapor Deposition

Films of SiO2, W and W/SiO2 have been applied as masks for the selective epitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD). The deposition selectiveties on SiO2 masks are mainly due to a difference in the absorption coefficients of reactant species between SiO2 and GaAs, while those on W masks are due to the surface migration of reactant species. Reactant species migrating on the surfaces of W masks are (finally) used in the epitaxial growth of opening windows, and selective epitaxial growth maintaining mask surfaces completely free from deposition have been attained for samples in which mask patterns are narrower than 40 µm.

Selective Epitaxial Growth of AlGaAs by Atmospheric Pressure –MOCVD Using Diethylgalliumchloride and Diethylaluminiumchloride

Selective epitaxy of AlGaAs was carried out by atmospheric pressure-MOCVD using DEGaCl and DEAlCl. In the case of Al composition of 0 and 0.16, polycrystal deposition on SiO2 masks was drastically suppressed at the growth rate below 0.020 µm/min. Even, in case of high Al composition of 0.43 and 0.73, a high selectivity of the deposition could be realized as long as the growth rate was kept below 0.017 µm/min. The high selectivity of the deposition can be explained by reevaporation of the reactant species in the form of GaCl and AlCl on the masks. Extremely flat surfaces were also obtained for GaAs selective epilayers grown below substrate temperature of 750°C and growth rate of 0.02 µm/min. In case of Al0.16Ga0.84As selective growth, ridge growth appeared in spite of growth conditions of 0.02 µm/min and 730°C. It is proposed that the ridge growth is related with vapor-phase diffusion from mask areas.

Zinc-doped GaAs epilayers grown by atmospheric-pressure MOCVD using diethylzinc

Abstract Diethylzinc (DEZ) was used as a p -type dopant in GaAs epilayers grown by atmospheric-pressure metalorganic chemical vapor deposition (AP-MOCVD) using trimethylgallium (TMG) and arsine (AsH 3 ) as source materials. Within a growth rate range of 0.05—0.20 μm/min, the hole concentration is independent of the growth rate and increased linearly and/or superlinearly with an increase in DEZ molar ratio. The doping efficiency depends not only on the concentration of Ga vacancies but also on the re-evaporation rate of Zn atoms adsorbing on the surface. The hole concentration shows a saturation in the region of a high DEZ molar ratio, and the maximum value of 3.5 × 10 20 cm −3 was obtained at a substrate temperature of 620°C. The saturation of the hole concentration suggests the occurence of clustering of Zn atoms on the surface and the generation of droplets of Ga-Zn alloys for a further increase of the DEZ molar ratio.

Surface‐diffusion model in selective metalorganic chemical vapor deposition

Selective epitaxial growth of GaAs was carried out by atmospheric pressure‐metalorganic chemical vapor deposition using W and SiO2 masks, and a deposition‐free region was clearly observed along the edge of the masks. The surface concentration of the reactant species on the masks was analyzed by a surface‐diffusion model and a new method to estimate the surface‐diffusion length on the masks was proposed. The surface‐diffusion length on SiO2 and W masks were 0.45 and 0.07 μm at 610 °C, respectively. The surface‐diffusion length increased with decreasing the substrate temperature and became longer on the masks irradiated by an atom beam.

Si‐doped GaAs epitaxial layers grown by metalorganic chemical vapor deposition

Silane is used as a doping gas for epitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD). The electron concentration mainly depends on the silane flux, but the doping efficiency is affected by the partial pressure of arsine. The Si‐doped epitaxial layers show a broadband spectrum of photoluminescence at 915 nm in addition to band‐edge spectrum, which originates from self‐activated complex of (V)Ga–SiGa. It appears from the dependence of 915‐nm spectrum on the arsine molar fraction that Ga vacancies increase with the increase of the partial pressure of arsine in the epitaxial growth of GaAs by MOCVD.

Selectively buried epitaxial growth of GaAs by metalorganic chemical vapor deposition

Selectively buried epitaxial growth of GaAs was attempted by metalorganic chemical vapor deposition using SiO2 films and W/SiO2 films as mask materials. Lateral supply of reactant species from mask areas to grooves occurred, which brought about the dependences of growth rate upon the width and the depth of grooves and produced swells near the groove edges. By use of W/SiO2 masks patterned narrower than 40 μm, grooves were selectively buried by epitaxial layers without accompanying polycrystal deposition on the masks.

Analysis of Deposition Selectivity in Selective Epitaxy of GaAs by Metalorganic Chemical Vapor Deposition

In GaAs-selective epitaxy by atmospheric-pressure MOCVD using W and SiO2 masks, the observed difference of the deposition conditions can be explained by two different mechanisms of heterogeneous nucleations (HN) on the mask surfaces. One is HN on ideally flat mask areas (case I), and the other is HN at irregular nuclei on the mask surfaces (case II). Surface concentration of reactant species on masks is analyzed by applying the surface-diffusion model to reactant species on the masks, and, for case I, the calculated results of polycrystal deposition on W and on SiO2 masks are compared with experimental ones. It becomes apparent that the occurrence of the thick polycrystal deposition frequently observed on W masks is due to high surface concentration. Products of the surface-diffusion coefficient and the stagnantlayer thickness are estimated as 6.25 cm3/s for W masks and 169.5 cm3/s for SiO2 masks at 610°C.

Lateral growth on {111}B GaAs substrates by metalorganic chemical vapor deposition

Abstract Laterally grown epitaxial layers from side walls of grooves prepared on {111}B GaAs substrates were obtained without occurrence of vertical growth by metalorganic chemical vapor deposition (MOCVD). {110} facets and {115}B facets appeared at the growth front of layers growing laterally in 〈112〉A and 〈112〉B directions, respectively. Lateral growth rates decreased monotonically from a maximum value in 〈112〉A direction to a minimum value in 〈112〉B direction. Crystal-orientation dependence of the growth rate is explained by the stability of kink sites on the facets, and the dependence of the stability originate from the number of dangling bonds per site.

Scanning tunneling microscope with gallium arsenide microtip fabricated by selective epitaxial growth

GaAs microtip for scanning tunneling microscope was fabricated by selective metalorganic chemical vapor deposition. The GaAs tip was constructed by two {111}B growth facets and a cleaved (110) surface. The surface of the GaAs tip was treated by ammonium sulfide solution, and highly oriented pyrolytic graphite surfaces were observed by using the GaAs tip in air. As the result, imagings of the atomic arrangement could be successfully obtained.