OBSERVATIONS OF 2 SEPARABLE PHOTOQUENCHING PHENOMENA IN LIGHTLY N-TYPE BULK GAAS BY OPTICAL-ABSORPTION, HALL-EFFECT, AND POSITRON-ANNIHILATION

We show that two different types of photoquenching effect take place u nder low temperature illumination of lightly n-type bulk GaAs. Both ph enomena result in an increase in positron trapping at vacancies, The f irst associated with a decrease in EL2 absorption, is produced with li ght of 1.1 mu m wavelength and recovers near 100 K. While little photo quenching related to EL2 is observed after illumination close to the b and edge (0.83 mu m), persistent increases in Hall voltage and positro n lifetime accompanied by a decrease in near band-edge absorption are observed. These latter phenomena recover at 50 K. (C) 1996 American In stitute of Physics.