Investigation of defects in low-temperature-grown GaAs using optical transient spectroscopy

Optical transient current spectroscopy (OTCS) has been used to investigate defects in the low-temperature-grown GaAs after postgrowth rapid thermal annealing (RTA). Two samples A and B were grown at 220°C and 360°C on (0 0 1) GaAs substrates, respectively. After growth, samples were subjected to 30 s RTA in the range of 500–800°C. Before annealing, X-ray diffraction measurements show that the concentrations of the excess arsenic for samples A and B are 2.5×10¹⁹ and 1×10¹⁹ cm⁻³, respectively. It is found that there are strong negative decay signals in the optical transient current (OTC) for the annealed sample A. Due to the influence of OTC strong negative decay signals, it is impossible to identify deep levels clearly from OTCS. For a comparison, three deep levels can be identified for sample B before annealing. They are two shallower deep levels and the so-called As_Ga antisite defect. At the annealing temperature of 600°C, there are still three deep levels. However, their structures are different from those in the as-grown sample. OTC strong negative decay signals are also observed for the annealed sample B. It is argued that OTC negative decay signals are related to arsenic clusters.