Anti-Stokes luminescence in nitrogen doped GaAs

In indirect band gap ${\rm GaAs}_{1-x}{\rm P}_x$ alloys, the Nx levels of the excitons bound to nitrogen have been resonantly excited. The detection of the photoluminescence (PL) at energies greater than the excitation energy (Anti-Stokes Luminescence (ASL)) shows a new PL band which appears at temperatures lower than 40 K. Its mean energy 2.205 eV is nearly independent of the alloy composition. We investigate ASL as a function of excitation photon energy, excitation power and temperature. Moreover ASL has been time resolved