Thermal conversion of AlxGa1−xAs layers grown by molecular beam epitaxy

We report the observation of thermal conversion of AlxGa1−xAs alloys grown by molecular beam epitaxy (MBE) from undoped, high-resistivity AlxGa1−xAs to low-resistivity, p-type material after annealing beyond the growth temperature (∼650 °C). The phenomenon occurs only in the Al-containing layers and not in the GaAs. Electrical measurements indicate that a substantial concentration of residual C acceptors causes the thermal conversion of the AlxGa1−xAs layers. A possible mechanism of C incorporation during MBE is examined from a thermodynamical point of view.