Tunneling spectroscopy of midgap states induced by arsenic precipitates in low-temperature-grown GaAs

The scanning tunneling microscope is used to study arsenic precipitates in low-temperature-grown and annealed GaAs. Tunneling spectroscopy reveals a distribution of states throughout the band gap, arising from the precipitates, with the density of midgap states increasing as the precipitate size increases. The Fermi level is found to be pinned at EV+0.65 eV for 600°C annealed material. For 800°C annealed material the Fermi level is located at EV+1.05 eV in regions far from precipitates, and additional depletion regions are observed near the precipitates.