CARRIER LIFETIME VERSUS ANNEAL IN LOW-TEMPERATURE GROWTH GAAS

The photoexcited carrier lifetimes in ex situ-annealed low temperature growth GaAs are measured with a femtosecond transient absorption experiment. The study encompassed two low temperature growth GaAs films with approximately 0.3% and 0.9% excess arsenic incorporated during growth. The observed lifetimes are found to be a function of the spacing of arsenic precipitates formed during the 30 s anneals to temperatures between 650 and 1000-degrees-C. The carrier lifetime for unannealed films was found to be less than approximately 200 fs. The carrier lifetimes increased from approximately 2 to approximately 10 ps as the average precipitate spacing was increased from approximately 400 to approximately 900 angstrom. These results are in sharp contrast to recent reports of subpicosecond lifetimes in similar GaAs annealed at 600-degrees-C.