ELECTRON-PARAMAGNETIC-RESONANCE STUDY OF SE-DOPED ALSB - EVIDENCE FORNEGATIVE-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 nonparamagnet ic. After illumination with white light from a tungsten source a stron g, persistent EPR signal with an isotropic g factor of 1.949 is observ ed. The metastability of the signal is consistent with earlier work do ne 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 e ffective-mass state of the defect, which is not filled at thermal equi librium. A detailed analysis of the line shape reveals that the linewi dth is determined by hyperfine interactions. The extent of the wave fu nction is found to be comparable to the predicted value of the effecti ve-mass state.