Masahiro Kakehi

Thermodynamics of Vapor Growth of ZnSe-Ge-I2 System in Closed Tube Process

The transport phenomena of ZnSe-Ge-I2 system in the closed tube process are thermodynamically investigated by means of the general transport equations presented in a previous paper.1) Calculations show that the nature of the transport reaction is mainly governed by the density of charged iodine. If the density is low enough, the main reaction is the thermal decomposition of ZnSe, while if it is high enough, the reaction is governed by the disproportionation reaction between GeI2 and GeI4. During the growth process a considerable amount of Ge is etched away by iodine vapor.

Sheet Resistivity of the Epitaxially Grown Germanium Layer

The vapor deposited layer of germanium usually contains a considerable number of lattice imperfections lowering its resistivity. The distribution of the defect concentrations is not uniform over the grown layer; it is maximum at the interface between the substrate and the grown layer and it decreases as leaving the interface, to disappear almost perfectly at a distance 10~20 µ from the interface. Such a non-uniform distribution is essentially the same, whether the layer will be produced through the open tube or the closed tube process, and whether they will be vapor-etched in situ or not. The results suggest that the mechanism producing the imperfection centers is determined by the surface condition of the substrate or the existence of non-equilibrium adsorption state.

Epitaxial Vapor Growth of Gallium Antimonide

Epitaxial vapor growth of gallium antimonide in the closed tube process is studied using polycrystal gallium antimonide and hydrogen chloride as the source crystal and the transport agent respectively. The transport rate is maximum when the hydrogen chloride concentration initially charged in the reactor is about 10-7 mole per unit volume. The surface morphology of the grown layer is strongly dependent on the pretreatment of substrate surface: The grown layer is mirror-smooth when the substrate surface is vapor-etched in situ for about 30 minutes preceding to the deposition. The electrical properties of the grown layers are studied by using the Pauws method. The hole concentration in the grown layer obtained in the routine experiment is comparable to or smaller than the lowest value ever reported (3~4×1016 holes/cm3), and the hole mobility ranges from 700 to 800 cm2/Vsec without any indication of compensation.

Epitaxial vapor growth of gallium antimonide

Abstract The epitaxial vapor growth of gallium antimonide in the conventional closed tube process was studied by using polycrystalline gallium antimonide as a source material. The transport agents used were hydrogen chloride, antimony penta-chloride and iodine. The growth rates were found to range from 0.5 to 10 μm/ hr when the initially charged amount of the transport agent was from 10 −8 to 10 −6 mole/cm 3 . The electrical properties of the grown layers were studied by the Van der Pauw method 1 ). The minimum of the hole concentration in the grown layer was 1.5−2 X 10 16 /cm 3 and the mobility was larger than 700 cm 2 /V sec. The p-n junction diodes were also prepared by using the same vapor growth technique. They had good rectification characteristics. The surface morphology of the grown layer was strongly dependent on the pretreatment of substrate surface: The surface of the grown layer was very smooth when the substrate surface was vapor-etched for about 30 min prior to the deposition.

Low Temperature Vapor Growth of Zinc Telluride

The vapor growth of zinc telluride in the ZnTe-I2 system and also the ZnTe-Ge-I2 system were thermodynamically and experimentally studied by using the closed tube transport techniques. The growth of Te crystal was observed in the ZnTe-I2 system when the growth temperature was less than 900°C, and the transport rate decreased as the growth time increased. In this system, the convection flow largely affected the transport process and the deposition of Te was presumably attributed to the convection effect of the vapor phase. In the ZnTe-Ge-I2 system, however, neither the growth of Te nor the inclusion of Ge was observed in the crystal grown under the usual conditions, and the transport rate of ZnTe was large enough and almost independent of the growth time. In this system a large cystal of ZnTe was grown at a relatively low temperature of 700°C.

Electrical and Photoelectrical Characterization of n·GaxAl1-xSb–p·GaSb Heterojunction

A heterojunction of nGaxAl1-xSb–pGaSb was prepared by vapor-phase deposition in a conventional closed-tube system with iodine as a transport agent. Electrical and photoelectrical characterization was carried out on the heterojunction diodes. The I-V characteristics showed that η in the forward current varied between 1 and 2 in the experimental range 206–300 K. The C-V measurements indicated that the heterojunction was an abrupt one with a diffusion potential of 0.65 V. The spectral photovoltaic response gave a broad peak between 1.35 and 1.55 µm.

Preparation and Electrical Properties of GaSb-Ge Heterojunctions by Vapor Growth Technique

GaSb-Ge heterojunctions having a large lattice misfit (8%) are fabricated by a conventional closed tube process in which Ge (p- and n-type) and SbCl5 used as a substrate and a transport agent, respectively. The substrate and source temperatures are ranged from 600°C to 650°C and from 650°C to 675°C, respectively. The epitaxial layer of GaSb is a p-type single crystal, so a pGaSb–nGe structure is obtained if n-Ge is used as a substrate. When the substrate is p-Ge, Sb diffused into the Ge to produce a pGaSb–nGe–pGe structure during the deposition. The V–I characteristics of these heterojunctions are explained satisfactorily on the basis of the Ribens multi-step tunneling model.

Vapor Growth of Al-Doped ZnTe by the Closed-Tube Method

The vapor growth of n-type ZnTe on as-grown ZnTe and GaSb substrates was examined at comparatively low temperature by the conventional closed-tube process using minute amounts of iodine as the transport agent. Polycrystalline ZnTe doped with either 5 or 10 mol% Al was used as the source crystal in the doping experiment. A uniform over-growth of ZnTe on the substrates was observed when iodine at a density of 0.6–13×10-5 mg/cm3 was introduced into the reaction tube and vapor growth in the 650–675°C system was carried out rather than in the 600–625°C or 625–650°C systems. SIMS measurement showed that the ZnTe layer was doped with a considerable amount of Al. The hot-probe method showed n-type conduction in the layer.