Scanning-tunneling-microscopy-induced optical spectroscopy of a single GaAs quantum well

We have investigated the scanning-tunneling-microscopy-induced light emissi on originating from a single GaAs quantum well. The 5-nm-thick quantum well was confined between a 30-nm-thick AlAs barrier (grown onto a GaAs substra te) and the vacuum tunneling gap. Low currents ensured a nonintrusive inves tigation of the surface. Optical spectroscopy of the light emitted while in jecting electrons from the tip revealed two peaks associated with the band- to-band recombination in the bulk GaAs (at 1.43 eV), and with the electroni c transition in the surface quantum well (at 1.52 eV). The surface sensitiv ity of the technique is evidenced and the quantum efficiencies of both proc esses are estimated. (C) 2000 American Institute of Physics. [S0003-6951(00 )03149-1].