BEHAVIOR OF EXCESS AS IN NONSTOICHIOMETRIC SI-DOPED GAAS

The Si doping efficiency (=[e-]/[Si]) in homoepitaxial GaAs has been measured as a function of molecular beam epitaxial growth conditions (As pressure, substrate temperature, and growth rate) and post-growth thermal annealing conditions. The doping efficiency decreases from one under optimal growth conditions to almost zero: (1) exponentially with inverse substrate temperature below 400-degrees-C and (2) as a power law in the As4-to-Ga beam-equivalent fluence ratio above unity. The doping efficiency of nonoptimally grown films increases from almost zero to near one upon post-growth thermal annealing above 650-degrees-C with slower than exponential kinetics. These changes are attributed to charge trapping into and release from, respectively, excess-As-related defects, which are incorporated during growth and removed by out-diffusion during annealing.