The sulfur-related trap in GaAs1−xPx

A systematic study has been made of the deep level introduced into GaAs1−xPx alloy material by S doping. Conclusive documentation of the linear relationship between S concentration and the deep-level trap concentration is presented for x?0.4. The dynamic properties of this trap measured at x=0.38 show a temperature activation energy for emission and electron capture of 0.35 and 0.15±0.03 eV, respectively. It exhibits a very large hole-capture cross section at a site occupied by an electron. A very sharp drop in the ability to populate the trap below x=0.35 is consistent with the trap being energetically tied to the X band minimum and having a depth of 0.17 eV below this band minimum. The dependence of the thermal-emission activation energy on alloy composition is ascribed to the necessity to capture electrons from the indirect minima below x?0.4. Photoionization experiments indicate that a much greater photoenergy than the thermal energy is required to ionize an electron trapped at this site (1.1 compared to 0.17 eV). Electron capture followed by a large lattice relaxation is consistent with the data and the phenomenon of persistent photoconductivity at low temperature associated with the S center. The S center in GaAs1−xPx provides an efficient nonradiative recombination path for minority carriers.