P. Stallinga et al., ELECTRON-PARAMAGNETIC-RESONANCE STUDY OF SE-DOPED ALSB - EVIDENCE FORNEGATIVE-U OF THE DX-CENTER, Physical review. B, Condensed matter, 52(12), 1995, pp. 8609-8612
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.