Recovery of quenched hopping conduction in GaAs layers grown by molecular-beam epitaxy at 200 °C

The dark current at 82 K, in GaAs layers grown by molecular-beam epitaxy at 200 °C and annealed at 550 °C, is reduced by a factor 350 after 5 min of IR (hν≲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×${10}^8$ exp(-0.26/kT), very close to the rate observed for EL2 (${\mathrm{As}}_{\mathrm{Ga}}$). This proves that the conduction below 300 K in this material is due to hopping between ${\mathrm{As}}_{\mathrm{Ga}}$-related centers in their ground states. Variable-range hopping [exp-(${\mathit{T}}_0$/T${)}^{1/4}$] gives a slightly better fit to the data than nearest-neighbor hopping [exp(-${\mathrm{\epsilon }}_3$/kT)] in the range T=82–160 K, but the fitted recovery rate is not strongly affected no matter which mechanism is assumed.