Lifetimes of photogenerated electrons on a GaAs surface affected by nanostructural defects

The recombination dynamics of photogenerated carriers on temporal and spatial scales of 100 fs and 100 nm, respectively, on an inhomogeneous GaAs surface with structural defects was investigated using time-resolved photoemission electron microscopy with femtosecond laser pulses. The observed photocarrier lifetimes (τ) ranged from subpicoseconds to picoseconds at isolated structural defects and were inversely proportional to the photoemission intensity at each defect. We concluded that τ corresponds to the carrier trapping time to midgap defect states and estimated the density of the midgap states at each defect on the basis of the relation between τ and the photoemission intensity.