The deep donor (DX center) in GaAs: determination of the entropy term in the activation energy

We present the first determination of the entropy term in the activation energy of the deep donor (DX center) in Si-doped GaAs. The equilibrium free carrier concentration is modeled assuming a deep level with either a one electron (positive U) or a two-electron (negative U) ground state. Different, but physically reasonable values of the entropy are obtained for the two models, and the data are consistently fit by either model over the accessible temperature range. Similar results are obtained in lightly Si-doped AlxGa1-xAs samples. (author) 9 refs., 3 figs., 1 tab