Annealing effects on heavily C doped GaAs and InGaAs films

The hole carrier concentration of heavily carbon doped GaAs epilayers (4.7×10¹⁹ and 9.8×10¹⁹ cm^-3) was increased and the mobility and lattice parameter were decreased by rapid thermal annealing silicon nitride capped samples at temperatures from 500 to 900°C. For the more heavily doped sample, the hole concentration, mobility, and lattice mismatch decreased with increasing annealing temperature for annealing temperatures higher than 700°C, but the hole concentration and mismatch were still larger than those of the as grown samples. Two heavily carbon doped InGaAs samples (2.35×10¹⁹ cm^-3 and 2.05×10¹⁹) with low In mole fractions (1% and 8%) were furnace annealed with or without silicon nitride caps in H₂ containing 0.3% AsH₃ over the temperature range 500-800°C. The changes observed for the capped samples were similar to those observed for the RTA annealed GaAs films, but for the uncapped samples the changes in the carrier concentration, mobility, and lattice parameter were for the most part much smaller. The only exception is the large increase in the lattice parameter at the highest annealing temperatures in the films containing 1% In. SIMS results showed that annealing produced no change in the C concentration or distribution, but the hydrogen concentration decreased in all samples except the uncapped films annealed in AsH₃. We attribute the low temperature (≤ 700°C) results in all but the uncapped samples annealed in AsH₃ to the removal of hydrogen which had passivated the carbon acceptor. Little, if any, H is removed from the uncapped samples annealed in AsH₃ because there is a dynamic equilibrium between the outdiffusion of H from the as-grown film and the in-diffusion of H from the surface catalyzed decomposition of AsH₃. We attribute the high temperature results to a combination of hydrogen removal and the creation of compensation centers, and suggest that the tendency to form the recombination centers is less when the film contains more In.