Tetsuji Imai

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.

Substrate effect on the deposition of Zn3P2 thin films prepared by a hot‐wall method

Zn3P2 thin films have been deposited by a hot‐wall method on Pyrex glass and (100)GaAs substrates. For GaAs crystalline substrates, higher deposition rates were obtained at the same source and substrate temperatures than those for glass substrates. Layers deposited on (100) GaAs substrates showed stronger preferential (004)orientation of the tetragonal structure, and hence an improved columnar structure is obtained as compared with those on glass substrates. The films having higher crystalline quality deposited on GaAs substrates have room‐temperature resistivities as low as ∼10 Ω cm.

Some properties of Zn3P2 polycrystalline films prepared by hot‐wall deposition

Zinc phosphide (Zn3P2) thin films have been deposited by hot‐wall deposition technique on glass substrate, and the deposition behaviors as well as structural properties of deposited films are studied. The source temperature and the temperature difference between source and substrate mainly affect the growth rate. Scanning electron microscope observation indicates the growth of columnar structure perpendicular to the substrate, and highly oriented thin films along the c axis are confirmed by x‐ray diffraction analyses. The resistivity of the films is strongly related to the phosphorus composition X in Zn(1−X)PX, and the films having higher X show lower resistivity. The direct absorption edge is obtained as about 1.5 eV from the optical absorption data.

Effect of Uniaxial Stress on Germanium p-n Junctions

The stress effect on germanium Esaki- and ordinary diodes has been investigated when the stress is applied perpendicularly to the junction which is parallel to the (111) plane. No essential difference in the stress effect has been found between Esaki- and ordinary diodes so far as the ordinary diode current region is concerned. Stress-induced increase in forward current with constant slope of ln I vs V plots is interpreted in terms of changes in both mobility and intrinsic carrier concentration due to piezo-effect of germanium bulk. A large increase in forward current with stress accompanied by the decrease in the apparent slope of ln I vs V plots is attributed to the stress-induced recombination-generation current due to large local stress at the junction. A decrease in reverse current with uniaxial stress observed in heavily doped specimens is explained by the decrease in number of [111] light mass tunneling carriers due to piezo-effect.

Indium doping effects on vapor‐phase growth of ZnS on GaP

Single‐crystal layers of ZnS have been grown on GaP substrates in a hydrogen transport system. By the addition of In to the reactant agents, the orientation dependence of the growth rates of ZnS are reversed for (111)A and (111)B substrates. The improvement of crystallinity of the grown layers can be seen by the surface morphology observation and x‐ray and reflection high‐energy electron diffraction analyses. These phenomena are undoubtedly caused by the In‐incorporation effects during the epitaxial growth of ZnS.

The Effects of Iodine-Doping on the Hetero-Epitaxial Growth of ZnS on GaP Substrates

Single-crystalline ZnS layers have been grown on GaP substrates using an open-tube hydrogen transport system. By the addition of iodine to the reactant agents, the growth rate of ZnS on GaP(111)A decreased and that on GaP(111)B increased. These changes of the growth rates caused by the iodine-doping process were characterized as the opposite behavior compared with those for the indium-doping case. For the growth on the GaP(100) plane, the deposition region has largely shifted to lower temperatures, and higher growth rates, such as 5 µm/h, were obtained at considerably lower temperatures, such as 580°C. From an x-ray diffraction analysis, it was found that a significant improvement in the crystallinity of the grown layers on (100) substrates was caused by the doping of iodine. An improvement in the surface morphology for these layers was also clearly observed.

Growth and characterization of zinc phosphide crystals

Abstract Zinc phosphide crystals ( Zn 3 P 2 ) having a large grain size were grown with purified source materials, using a necked quartz ampoule in order to control the transport rate of the nutrients. The electrical characteristics of the sliced wafer were measured as a function of both of the position along the growth direction of the ingot and the phosphorus composition x in the Zn 1- x P x . The carrier concentration was found to vary along the growth direction. The electrical resistivity decreased from 10 3 to 10 2 Ω cm simultaneously with an increase in the phosphorus composition of the grown crystal.

Effect of substrate materials in the growth of ZnSe on GaAs and GaP substrates

ZnSe layers were grown on GaP and GaAs substrates by hydrogen‐transport vapor‐phase epitaxy. The influences of the substrate materials upon the growth rate and the lattice parameter of the ZnSe layers were studied. The ZnSe lattice parameter normal to the heterointerface was measured by using x‐ray diffraction. In the case of the growth on the (100) plane, a larger growth rate and better crystallinity on GaAs were obtained compared with growth on GaP. This strongly suggests that misfit strain together with dislocation formation is quite harmful to the growth of high‐quality heteroepitaxial layers. The layers were considered to be strained compressively in the normal direction to the heterointerface by thermal stress.

Dependence of substrate materials on the growth of ZnS on GaAs and GaP substrates

Abstract Single-crystalline ZnS layers have been grown on GaP and GaAs substrates, using a hydrogen transport system. The growth behavior on GaAs and GaP substrates is found to be strongly influenced by the auto-doping of gallium from the substrate. These phenomena are ascertained from the Ga-doping experiments in the ZnS growth process on GaP(111)A and B substrates. By the addition of Ga atoms to the vapor phase, the growth rate on (111)A decreases and that on (111)B increases, probably due to the change of the surface chemical reaction related to Ga atoms. These Ga-doping effects are found to show nearly the same behavior as those of In-doping for the growth of ZnS on GaP.

The effects of In doping on the heteroepitaxial growth of ZnS on GaP substrates

Single‐crystal layers of ZnS have been grown on GaP substrates in a hydrogen transport system. In order to clarify the doping effects of In on the growth behavior, some In‐doping experiments with various doping processes are performed. The reversal in the orientation dependence of the growth rate and the improvement of the crystallinity of the epitaxial layers are caused by the existence of In atoms and/or In compounds at the growing surface of ZnS. The In atoms and/or In compounds which exist at the interface between the GaP substrate and ZnS epitaxial layer are shown to have no significant effect on the growth behavior.