Electrical resistivity and Hall effect measurements were made of n-type material under uniaxial stressing in the [100] and [111] directions at low temperatures. After transformation of the EL2 defect into its metastable configuration, stress-induced decreases of the electron Hall concentration and mobility were observed. This effect was related to the capture of electrons by the acceptor state of the metastable EL2 defect ([EL2*]-/0). It was found that this level split, under a [111] stress, into 2 orientationally degenerate components (triplet and singlet). The dependence of the Hall concentration and mobility upon [111] stressing, as determined after EL2 photo-quenching under a high stress, was different to that measured after EL2 photo-quenching without an external stress. This difference was attributed to the ordering of metastable EL2 centers after photo-quenching under high stresses, and was consistent with the isolated AsGa model for the EL2 defect. The stress coefficients for [EL2*]-/0 sub-levels, split by [111] stressing, were found to be -0.017 and -0.041eV/GPa for the triplet and singlet, respectively. The level was not split by [100] stressing.

A.Babinski, A.Wysmolek, J.M.Baranowski: Physical Review B, 1994, 50[15], 10656-60