New metastable defects were observed in Si-doped Ga0.7Al0.3As layers which had been grown by means of metalorganic chemical vapor deposition, and irradiated with 1MeV electrons to doses ranging from 3 x 1014 to 3 x 1016/cm2 at 300K. Deep-level transient spectroscopic studies were carried out after prior isochronal and isothermal annealing. In the case of as-grown material, stable-state parameters with a thermal activation energy of Ec-0.17eV and an electron capture cross-section of 1.1 x 10-13cm2 were identified. These were identical to those of the defect which was formed during the irradiation of this material and which had been identified as being VAs. The parameters of the metastable state were Ec-0.21eV and 2.5 x 10-14cm2. The kinetics of the configurational transformations of the defect were first order. The thermal activation energies and pre-exponential factors were equal to 0.39eV and 1.0 x 1011/s for the transformation of the first defect above into the second one, and were equal to 0.23eV and 3.4 x 107/s for the reverse transformation. The metastable defect was supposed to include VAs, and perhaps a donor impurity. An increase in the concentration of metastable defects was observed in irradiated material. As in the case of as-grown material, the signature of the stable state was identical to that of the E1 defect, but the transformation mechanism was different. This was thought to be related to the formation of another pair: VAs-Asi. It was concluded that the value of the pre-exponential factor corresponded, in its order of magnitude, to an interstitial Asi single-jump process.

M.M.Sobolev, I.V.Kochnev, M.I.Papentsev, V.S.Kalinovsky: Semiconductor Science and Technology, 1996, 11[11], 1692-5