Abstract
A scanning tunneling microscope (STM) is used to investigate light emission induced by electron tunneling into GaAs. Reproducible results are obtained in air on cleaved (110) surfaces passivated with a thin (∼ 1.6 nm) gold film. The luminescence spectrum is dominated by recombination of thermalized electron-hole pairs. In p-type material, the light emission threshold is at 1.45 V bias voltage, close to the band gap at 300 K. The quantum efficiency of this minority-carrier injection process increases quadratically with increasing bias voltage. In n-type material, the current induced edge emission occurs at a much higher threshold of U > 3.2 V, giving evidence for the onset of hole production via impact ionization by the injected hot electrons.
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