Mitsuo Furukoshi

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Abstract Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl4-H2O and SnCl4-H2O2 reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 102–10-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.

Direct observation of the 3C-2H transformation in ZnSe by high-temperature x-ray diffraction

Abstract The crystal structures of ZnSe at high temperatures up to 1440°C are directly observed by a high-temperature oscillation technique. ZnSe samples cut from melt-grown crystals with a zincblende structure are sealed in fused quartz ampoules to avoid sublimation. The ampoule is fixed in a graphite heater. An X-ray diffraction study of the structural transformation in ZnSe is performed through the graphite heater. The X-ray patterns by the 12° oscillation method with Cu K α show that the cubic zincblende (3C) structure of ZnSe transforms to the hexagonal wurtzite (2H) structure above a reported transition temperature of 1425°C and that the 2H to 3C transformation in ZnSe occurs by cooling.

Formation of defects in zinc selenide crystals grown from the melt under argon pressure

The formation of macroscopic defects in ZnSe crystals is described. Crystals were grown by the Bridgman technique at the lowering rate of a crucible of 0.8–10.1 mm/h under an argon pressure of 100 kg/cm2. The formation of the assembly of rod-like low angle grain boundaries was dependent upon the angle θ between the growth axis and the (111) twin plane normal. For 75° < θ < 90° the rod-like low angle grain boundaries occurred and for θ < 75° crystals free of the boundaries grew at the lowering rates used in our experiments. The formation of voids was dependent on the lowering rate of the crucible. Many crystals free of these defects were obtained in the growth range 0.8–2.5 mm/h.

Melt growth of ZnSe crystals under argon pressure

Abstract The growth conditions of ZnSe crystals from the melt under an argon pressure of 100 kg/cm2 by the Bridgman technique are described. The temperature distributions in a high pressure furnace and the lowering rate of a graphite crucible were varied. The composition of the quenched melts was determined by chemical analysis of Zn. The excess Se in the melt is one of the important factors which limit the growth rate of ZnSe single crystals.

Growth of ZnSe crystals from the melt under Zn partial pressure

Abstract This paper describes melt growth of ZnSe crystals by a modified Bridgman method under argon pressure. Stoichiometric deviations of the ZnSe melt are controlled by Zn partial pressure. A crucible and a Zn reservoir are placed in a pyrolitic boron nitride (pBN) vessel, which is covered with a deep, closed pBN cap to minimize loss of Zn. A definite Zn partial pressure over the melt during growth is maintained by controlling the temperature of the Zn reservoir. The melt composition is analyzed as a function of the temperature of the Zn reservoir. The stoichiometric melt is obtained under Zn partial pressure. Low-resistivity n-type crystals of 0.2-0.9 Ω cm are grown from Zn-rich melts in a one-step process.

Solution growth of ZnSe crystals using In-Zn solvents

Abstract Measurements of liquidus solubility of ZnSe in In-Zn solvents are made in the range of 0 to 100% Zn solvent composition at temperatures of 700 to 1150°C. The solubility decreases steeply with increasing Zn concentration in the solvents. ZnSe crystals with the zincblende arrangement are obtained from the solutions. Electrical properties are measured on the crystals by the van der Pauw method. Free-electron concentration is dependent on the solvent composition and the cooling rate after growth. Highly conductive ZnSe (of the order of 0.1 ohm cm) is obtained from In-Zn solutions of more than 50% Zn. Redistribution of In in the grown crystals is also discussed.

Growth of ZnSe crystals free from rod-like low angle grain boundaries from the melt under argon pressure

Abstract ZnSe crystals free from rod-like low angle grain boundaries are reproducibly grown from the melt under a small temperature gradient of 12–22°C/cm by the Bridgman method under argon pressure. Because the ZnSe melt under argon pressure is highly supercooled, crucibles used under such small temperature gradients should be designed to compensate for the large supercooling. The supercooling is related to the melt composition, which is Se rich.

Growth and Properties of Low-Resistivity n-Type ZnSe Crystals Grown from the Melt with Excess Zn under Argon Pressure

This paper describes a technique for growing low-resistivity n-type ZnSe crystals from the melt under pressure and the electrical and optical properties of the crystals. The low-resistivity ZnSe crystals are grown from the melt with excess Zn of 3 to 9.3 mol%. The resistivity of the crystals is of the order of 0.1 Ωcm and the electron Hall mobility is 220 to 380 cm2/Vs. Near-band-edge emission is observed from the low-resistivity ZnSe crystals at room temperature in photoluminescence measurement.

The electrical properties and impurity profiles of ZnSe films on GaAs and of Gallium-diffused ZnSe single crystals

Abstract The electrical properties and impurity profiles of ZnSe films and gallium-diffused ZnSe single crystals were investigated. ZnSe films 10–30 μm thick were epitaxially grown on p-type GaAs in the vapour phase by using metallic zinc and metallic selenium without intentional doping. Low resistivity films (of the order of several ohm centimetres) were deposited, even in the presence of excess selenium, at temperatures above 650°C. The carrier concentration profile showed an exponential dependence on the distance from the interface. Donor and acceptor concentrations of about 10 18 cm -3 and a compensation ratio close to unity were obtained. An electron probe microanalyser was used to determine the impurity profiles on the cleaved surfaces. Gallium and arsenic atoms were distributed exponentially throughout the ZnSe films with concentrations of the order of 10 20 cm -3 . The gallium concentration was always higher than the arsenic concentration. The concentration of the electrically active impurity was about two orders of magnitude less than the gallium and arsenic concentrations. The gallium-diffused ZnSe was prepared in an evacuated quartz ampoule by diffusing gallium from the melt into a melt-grown ZnSe single crystal in order to compare the electrical properties of gallium-diffused and undiffused ZnSe. The resistivity of the gallium-diffused ZnSe was also low. We conclude from these results that the resistivity of ZnSe on GaAs became low because of gallium auto-doping. The gallium concentration profile in the bulk ZnSe was described by a complementary error function in contrast with the exponential distribution obtained for ZnSe films on GaAs. A trial solar cell of dimensions 4 mm x 4 mm had an open-circuit voltage of 0.65–0.75 V and a short-circuit current of 0.9–2.2 mA.

Vapor Phase Epitaxial Growth of Highly Conductive P -Type ZnSe Films with Codoping of P and Li

Highly conductive p-type ZnSe films were grown at 450–500°C onto (100)GaAs by vapor phase epitaxy with codoping of P and Li. Vapors of Zn, Se and impurities were transported separately to the vicinity of the substrates. Hall effect measurement revealed that p-type films were degenerate. When either only P or Li was doped, the resistivity was very high and its conductivity type was unknown. The SIMS analysis showed a uniform profile of both impurities in the p-type epitaxial film: the Li concentration was estimated as 1019 cm-3; P was an order of 1018 cm-3 with the aid of EPMA.