Formation of etch pits during carbon doping of gallium arsenide with carbon tetrachloride by metalorganic vapor-phase epitaxy

Scanning tunneling microscopy was used to examine the effects of carbon tet rachloride concentration and temperature on the morphology of carbon-doped gallium arsenide films grown by metalorganic vapor-phase epitaxy. Depositio n was carried out at 505-545 degrees C, a V/III ratio of 75, and IV/III rat ios between 0.5 and 5.0. The growth rate declined monotonically with increa sing carbon tetrachloride concentration. Step bunching and pinning was obse rved at a IV/III ratio of approximately 2.5. Increasing this ratio further resulted in the formation of pits ranging from 20 to 50 nm in diameter. The se results can be explained by two competing processes that occur at the st ep edges: (1) the reaction of chlorine with adsorbed gallium from the group III precursor, and (2) the reaction of chlorine with gallium arsenide. Bot h reactions desorb gallium chlorides and reduce the growth rate, but only t he latter reaction produces pits. (C) 1999 American Institute of Physics. [ S0021-8979(99)06213-1].