Electron Paramagnetic Resonance Study of Se-Doped AlSb: Evidence for Negative-U of the DX Center

A metastable electron paramagnetic resonance signal is observed in Se doped AlSb. After illumination a strong, persistent electron paramagnetic resonance signal with an isotropic g-factor of 1.949 is observed. The absence of any electron paramagnetic resonance when cooled in the dark is direct evidence for the negative-U model. The electron paramagnetic resonance arises from the effective-mass state of the defect, which is not filled at thermal equilibrium. An analysis of the lineshape reveals that the linewidth is determined by hyperfine interactions. The extend of the wave function is found to be comparable to the prediction for the effective-mass state.