THE BONDING OF C-AS ACCEPTORS IN INXGA1-XAS GROWN BY CHEMICAL BEAM EPITAXY USING CARBON TETRABROMIDE AS THE SOURCE OF CARBON

InxGa1-xAs layers (0 less than or equal to x less than or equal to 0.3 7) doped with carbon (>10(20) cm(-3)) were grown on semi-insulating Ga As substrates by chemical beam epitaxy using carbon tetrabromide (CBr4 ) as the dopant source. Hall measurements imply that all of the carbon was present as C-As for values of x up to 0.15. The C accepters were passivated by exposing samples to a radio frequency hydrogen plasma fo r periods of up to 6 h. The nearest-neighbor bonding configurations of C-As were investigated by studying the nondegenerate antisymmetric hy drogen stretch mode (A(1)(-) symmetry) and the symmetric X(H) mode (A( 1)(+) symmetry) of the H-C-As pairs using IR absorption and Raman scat tering, respectively. Observed modes at 2635 and 450 cm(-1) had been a ssigned to passivated Ga4CAs clusters. New modes at 2550 and 430 cm(-1 ) increased in strength with increasing values of x and are assigned t o passivated InGa3CAs clusters. These results were compared with nb in itio local density functional theory. Modes due to AlInGaCAs clusters were detected in samples containing grown in Al and In. These results demonstrate that for InGaAs, CBr4 is an efficient C doping source sinc e both In-C-As bonds as well as Ga-C-As bonds are formed, whereas ther e is no evidence for the formation of In-C-As bonds in samples doped w ith C derived from trimethylgallium or solid sources. (C) 1996 America n Institute of Physics.