Excitation photocapacitance study of EL2 in n-GaAs prepared by annealing under different arsenic vapor pressures

The excitation photocapacitance method was applied to n-GaAs:Te (n=4 × 10¹⁶ cm^-3) prepared by annealing under various excess arsenic vapor pressures. By changing the primary excitation photon energies, the emission spectra for the EL2⁰→EL2⁺ and EL2⁺→EL2⁺⁺ transitions were determined. Considering the electron capture processes of the valence band (VB)→EL2⁺ (0.67 eV) and VB→EL2⁺⁺ (0.47 eV) at 77 K, the Frank-Condon shifts (d_FC) of the annealed GaAs crystals were determined for the EL2⁺ level on the basis of the configuration coordinate model. It was shown that the lattice relaxation around the EL2 level is larger under arsenic-poor conditions, and thus it is considered that arsenic vacancies are closely related with the atomic configuration of the EL2 defect, in combination with excess arsenic defects.