Growth mechanism in heavily carbon-doped GaAsxSb1−x grown by MOCVD

The InP/GaAsSb material system has type-II band structures and can provide ideal band structures for HBT operation. For the fabrication of HBTs, the growth of p-GaAsSb, which is used as a base layer in HBT structures, must be clarified. We investigated the change of GaAsSb growth behavior that occurs by adding CBr4 as a p-type dopant gas. As the CBr4 partial pressure in the vapor phase increased, the growth rate and Sb composition of the GaAsSb layer decreased. The CBr4 partial pressure dependence of growth rate is well interpreted by the formula derived from two chemical equilibrium equations: one the pyrolysis static reaction of CBr4, and the other the etching static reaction between HBr and Ga. From the fitting formula, GaSb in GaAsSb is found to be etched three times faster than GaAs in GaAsSb, resulting in a decrease of Sb composition in the GaAsSb solid phase with an increase of CBr4 partial pressure. Additionally, the growth rate of C-doped GaAsSb is found to be independent of the V/III ratio, although Sb composition in the solid phase monotonically decreased with increasing V/III ratio.