Optical Memory Effect based on Deep Level Filling and Depletion in Semi-Insulating Materials

Abstract

The absorption of a radiation pulse propagating through a semiconductor is described by non-linear time dependent photon transport equations, which account for the effect of the radiation on the deep level electron population and conversely (photon energy is lower than the band gap). We consider optical pulse widths shorter than the propagation time in the sample. In such a case, the pulse trailing edge interacts with an electron population which has been modified by its leading part. Equations are solved in closed form for an arbitrary input pulse and an arbitrary initial electron distribution on deep levels. The solution is discussed for lorentzian pulses. The energy transmission ratio T = Etrans/Einc is calculated versus the optical capture cross-sections and the initial electron distribution; the case of two delayed pulses at different wavelengths is especially discussed. In optical data processing the first pulse is the writing pulse and the second is the reading one. The optical storage time dependence versus the semiconductor parameters is discussed. This model is used to analyze the transmission of picosecond pulses through GaAs:Cr-O samples at room temperature.