EFFECT OF THE CARBON ACCEPTOR CONCENTRATION ON THE PHOTOQUENCHING ANDFOLLOWING ENHANCEMENT OF THE PHOTOACOUSTIC SIGNALS OF SEMIINSULATING GAAS

The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon concentration controlled and not intention ally doped semi-insulating (SI) GaAs. The decrease of the PPA signal d ue to the photoquenching effect of EL2 is observed for a short period of illumination in the photon energy region from 1.0 to 1.3 eV. Since almost all of the carbon accepters are compensated by deep donor EL2 i n SI GaAs, electron occupancy of EL2 level can be controlled by changi ng the carbon acceptor concentration. It is found that the photoquench ing becomes drastic with increasing the carbon concentration. After fu lly photoquenching, the PPA signal increases again through a local min imum by the continuous light illumination and finally exceeds the init ial value before illumination until the saturation level is reached. T he deep donor level EL6 and its metastable state are proposed. EL6 lev el donates electrons to compensate a part of carbon accepters after EL 2(0) to EL2 transition is accomplished. The nonradiative recombinatio n through this level generates the PPA signal. Since the PPA measureme nt can detect lower concentration of EL6 than that of EL2, the higher sensitivity of the PPA measurements than the optical absorption measur ements is pointed out. The usefulness of the PPA technique for studyin g the nonradiative transition through deep levels in semiconductors is also suggested. (C) 1997 American Institute of Physics.