LUMINESCENCE FROM GAAS(100) SURFACE EXCITED BY A SCANNING TUNNELING MICROSCOPE

We have measured luminescence of atomically clean GaAs(100) samples in duced by a scanning tunneling microscope (STM) under ultrahigh vacuum (UHV) conditions. GaAs(100) samples were grown by molecular beam epita xy and capped with a thick arsenic overlayer to protect the surface du ring transfer through ambient atmosphere to the UHV STM chamber equipp ed with a light collection system. The luminescence arises from the ra diative recombination of the excited carriers across the band gap indu ced by the tunneling current. Maps of luminescence as a function of la teral position of the STM tip (photon maps) have been recorded. Arseni c related features of the size of similar to 20 nm appear as dark area s in the photon maps indicating increased local nonradiative recombina tion. Photon maps acquired at positive and negative sample bias show s ignificant differences in contrast. Mechanisms responsible for the STM excited luminescence and contrast observed in the photon maps are dis cussed. (C) 1997 American Vacuum Society.