STRAIN RELAXATION AND COMPENSATION DUE TO ANNEALING IN HEAVILY CARBON-DOPED GAAS

Heavily C-doped GaAs grown by atmospheric pressure metalorganic vapor phase epitaxy using CCl4 as the C-dopant source has been annealed to study the stability of C acceptors at very high doping levels (p = 10(18)-10(20) cm-3). In layers with initial hole densities p > 6 x 10(19) cm-3, 5 min anneals at temperatures ranging from 700 to 850-degrees-C under arsine overpressure caused a significant reduction in the hole density, lattice contraction and photoluminescence intensity, and a smaller reduction in the mobility. For lower doped material, annealing has little effect on the as-grown properties. These changes in the material properties indicate that a compensating recombination center is formed during annealing. Possible compensation mechanisms which explain partially the annealing effects in very heavily C-doped GaAs are analyzed. The results of this study show that there is an upper limit on the hole concentration of p > 6 x 10(19) cm-3 in annealed GaAs:C.