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

We have investigated the scanning-tunneling-microscopy-induced light emission 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 substrate) and the vacuum tunneling gap. Low currents ensured a nonintrusive investigation of the surface. Optical spectroscopy of the light emitted while injecting 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 electronic transition in the surface quantum well (at 1.52 eV). The surface sensitivity of the technique is evidenced and the quantum efficiencies of both processes are estimated.