Deep levels and carrier capture kinetics in n-GaAsBi alloys investigated by deep level transient spectroscopy

Dilute bismides (%Bi ∼ 1%-3%) are excellent candidates for the fabrication of optoelectronic devices, thanks to the strong reduction in the bandgap with increasing bismuth content, the weak temperature dependence of the bandgap, and the small Auger recombination coefficient for high bismuth concentrations. Since Shockley-Read-Hall recombination may significant impact on the electrical and optical properties of the devices, describing the defects within the semiconductor material is of paramount importance for the optimization of device technology. To this aim, this paper investigates the deep levels within the bandgap in un-annealed n-type GaAsBi grown by molecular beam epitaxy at low temperature (390 °C) by means of deep level transient spectroscopy and filling time-dependent measurements. The original results described in the paper indicate (a) the presence of four majority and two minority carrier traps, and (b) that, from the analysis of the charge-capture kinetics, the dominant electron and hole traps originate, respectively, from a dislocation-related and a point defect with capture barrier of 0.48 eV. In addition, (c) we demonstrate that the incorporation of bismuth in GaAs generates only one additional electrically active defect with concentration higher than the sensitivity of the measurement setup, because most of the relevant traps found in GaAsBi layers have been identified in pure GaAs grown at low temperature. Finally, (d) the trap concentration is relatively constant along the growth direction, indicating a uniform defect density.