CHARGE-STATE OF THE DX CENTER IN ALUMINUM GALLIUM-ARSENIDE FROM PHOTO-HALL MEASUREMENTS

We report the temperature dependence of the Hall mobility in the dark and in the persistent-photoconductivity (PPC) states of AlxGa1-xAs:Te and AlxGa1-xAs:Si samples, which incorporate buffer layers separating the epilayer from the substrate rhe mobility of the Si-doped sample is higher in the PPC state than in the dark, whereas for the Te-doped sa mple the mobility in the dark is higher. The results for the Si-doped sample can be explained equally well by the positive-U and the negativ e-U models of the DX center and hence are not suitable for drawing def initive conclusions about the charge state of the DX center. On the ot her hand, the results for the Te-doped sample are shown to be conclusi vely in favor of the neutral charge state (positive-U) model of the DX center.