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 “C!. The carrier lifetime for unannealed films was found to be less than -200 fs. The carrier lifetimes increased from -2 to 10 ps ‘as the average precipitate spacing was increased from -400 to -900 A. These results are in sharp contrast to recent reports of subpicosecond lifetimes in similar GaAs annealed at 600 “C.