New gaseous impurity and its effect on the purity of LPE GaAs

The present work describes a new gaseous impurity source of GaAs grown by the conventional liquid phase epitaxy. A large quantity of impurity gas of mass number 16 was detected in the LPE atmosphere even when H₂O vapour and O₂ residual gas were exhausted almost completely. The impurity gas was only detected in the presence of H₂ and a graphite boat at high temperature, and above 850°C this was exaggerated. From comparison of the mass-spectrum of standard gas, the impurity gas was identified as methane. An amount of 130 ppm of methane in H₂ resulted in a carrier concentration of LPE GaAs higher than 10¹⁶ cm^-3.