Abstract
Hall measurements were performed on molecular beam epitaxy grown AlxGa1-xAs:Si in the temperature range 77-300 K. The DX center has been detected through the observation of persistent photoconductivity at low temperature. Two statistics have been developed, using the negative-U model of Chadi and Chang, to analyze the temperature dependence of Hall electron densities. The first statistic is derived assuming that the conduction electrons originate exclusively from the DX center. The second statistic, however, supposes the existence of shallow donors and acceptors in addition to Si-DX centers. The concentrations of these centers are treated as fitting parameters. We have investigated, on the other hand, the pinning of the Fermi level E-F and the trend of the probability f(DX)(-) of Si to be in the DX- state versus temperature using the previous statistics. We will attempt to explain all these results. (C) 2000 American Institute of Physics. [S0021-8979(00)05210-5].