Shoichi Washizuka

Magnetic field effect on residual impurity concentrations for LEC GaAs crystal growth

Abstract A horizontal magnetic field applied LEC (MLEC) apparatus, for mass-producing large diameter undoped LEC GaAs, has been newley developed. The detailed magnetic field effect on residual impurity concentrations has been studied. The carbon and boron concentrations have been found to be decreased by the MLEC technique, related to the applied magnetic field strength. Carbon and boron impurity concentrations in MLEC GaAs crystals decreased as the gallium molar ratio in molten GaAs decreased. The carbon concentration in MLEC GaAs decreased by decreasing the argon pressure in a high pressure chamber. The thermochemical mechanism for impurity incorporation into GaAs single crystals has been clarified through this study. The oxidation rate of free gallium and deoxidation rate of carbon oxide are shown to be the rate limiting reactions determining the impurity incorporation rate into GaAs crystals. The obtained results suggest that applying a magnetic field to molten GaAs suppresses the chemical reaction closely related to the impurity incorporation into resultant GaAs single crystals. The experimental results show good agreement with this predicted thermochemical mechanism.

Stoichiometry of undoped LEC GaAs

Abstract Stoichiometry of undoped LEC GaAs has been studied by improved coulometric analysis. The solidus phase boundary shape of GaAs has been predicted, based on experimental results. The congruent point has been found to be on the slightly arsenic-rich side. The solidus boundary shape, extending on the gallium-rich side, has been suggested to be flat, while the other boundary, extending to the arsenic-rich side, has been suggested to be steep. The influence of temperature fluctuations, in the vicinity of the growing crystal-melt interface, on compositional variation along the crystals has been clarified. The magnetic field applied LEC (MLEC) GaAs crystals showed a clear relationship with a predicted solidus phase boundary shape, whereas conventional LEC crystals showed an ambiguous correlation.

Scatterings of Shallow Threshold Voltage on Si-Implanted WN Self-Alignment Gate GaAs Metal-Semiconductor Field-Effect Transistors on Different Composition 2-Inch Substrates by Growing in Three Kinds of Furnaces

Two-inch undoped GaAs crystal boules were grown from different composition melts in a pyrolytic boron nitride crucible in three kinds of furnaces in order to survey composition effect through a consecutive thermal cooling cycle after crystallization on Vth scattering of Si-implanted metal-semiconductor field-effect transistors (MESFETs). On the substrates (dislocation density: 2×103-105 cm-2 order) obtained from the crystal boules, a tungsten nitride self-alignment gate MESFET array of shallow Vth (3×1012 cm-2, 50 keV) was fabricated, and Vth scatterings were observed on them. The Vth scattering for the most As-rich melt-grown crystal boule in the furnace with the smallest ratio of bottom heating was the smallest as compared with those for the slightly Ga-rich or As-rich melt-grown crystal boules in the furnaces with the greatest ratio of bottom heating. There was an anticorrelation between the Vth scattering amplitude and carbon content in the substrate crystals.

Properties of high quality GaP single crystals grown by computer controlled liquid encapsulated Czochralski technique

The properties of GaP single crystals grown by an automatically diameter controlled liquid encapsulated Czochralski technique using a computer have been studied. A dislocation density less than 5×104 cm−2 has been observed for crystal grown in a temperature gradient lower than 70 °C/cm near the solid‐liquid interface. Crystals have about 10% higher electron mobility than that of commercially available coracle controlled crystals and have 0.2∼0.5 compensation ratios. Yellow light emitting diodes using computer controlled (100) substrates have shown extremely high external quantum efficiency of 0.3%.