RECOVERY OF QUENCHED HOPPING CONDUCTION IN GAAS-LAYERS GROWN BY MOLECULAR-BEAM EPITAXY AT 200-DEGREES-C

The dark current at 82 K, in GaAs layers grown by molecular-beam epitaxy at 200-degrees-C and annealed at 550-degrees-C, is reduced by a factor 350 after 5 min of IR (hnu less than or similar to 1.12 eV) light illumination. As temperature is swept upward at 0.2 K/s, the current recovers rapidly near 130 K. A numerical analysis of the current recovery, based on hopping conduction, gives an excellent fit to the data for a thermal recovery rate r = 3 X 10(8) exp (-0.26/kT), very close to the rate observed for EL2(AS(Ga)). This proves that the conduction below 300 K in this material is due to hopping between AS(Ga)-related centers in their ground states. Variable-range hopping [exp-(T0/T)1/4] gives a slightly better fit to the data than nearest-neighbor hopping [exp(-epsilon3/kT)] in the range T = 82-160 K, but the fitted recovery rate is not strongly affected no matter which mechanism is assumed.