ELECTRON-PARAMAGNETIC-RESONANCE STUDY OF SE-DOPED ALSB - EVIDENCE FOR NEGATIVE-U OF THE DX-CENTER

A metastable electron-paramagnetic-resonance (EPR) signal is observed in Se-doped AlSb. When cooled in the dark, the sample is nonparamagnetic. After illumination with white light from a tungsten source a strong, persistent EPR signal with an isotropic g factor of 1.949 is observed. The metastability of the signal is consistent with earlier work done on DX-like centers. The absence of any EPR when cooled in the dark is direct evidence for the negative-U model. The EPR arises from the effective-mass state of the defect, which is not filled at thermal equilibrium. A detailed analysis of the line shape reveals that the linewidth is determined by hyperfine interactions. The extent of the wave function is found to be comparable to the predicted value of the effective-mass state.