Effect of Ambient Gas on Undoped LEC GaAs Crystal

Undoped GaAs crystals were grown by the LEC technique from quartz crucibles in N2, He, Ar or Kr ambient gases. The influence of the ambient gases on the electrical properties and dislocation densities of the crystals was examined, and it was found that even when a quartz crucible was used, undoped GaAs crystals grown in N2 ambient became semi-insulating, while crystals grown in rare gases were n-type conductive. This effect of N2 was studied using secondary-ion mass spectrometry bulk analysis and low-temperature photoluminescence measurements. When the effect of the ambient gas on the Etch Pit Density (EPD) was investigated, dislocation densities were found to decrease in the order Kr, Ar, N2 and He, as expected from their heat transfer efficiencies.