On demand single photon source using a nanoscale   metal-insulator-semiconductor capacitor
  We propose an on-demand single photon source for quantum cryptography using a metal-insulator-semiconductor quantum dot capacitor structure. The main component in the semiconductor is a p-doped quantum well, and the cylindrical gate under consideration is only nanometers in diameter. As in conventional metal-insulator-semiconductor capacitors, our system can also be biased into the inversion regime. However, due to the small gate area, at the onset of inversion there are only a few electrons residing in a quantum dot. In addition, because of the strong size quantization and large Coulomb energy, the number of electrons can be precisely controlled by the gate voltage. After holding just one electron in the inversion layer, the capacitor is quickly biased back to the flat band condition, and the subsequent radiative recombination across the bandgap results in single photon emission. We present numerical simulation results of a semiconductor heterojunction and discuss the merits of this single photon source. 
Binhui Hu, C. H. Yang, and M. J. Yang