Si-doped AlxGa1−xN„0.56ÏÃÏ1… layers grown by molecular beam epitaxy

We describe experiments on Si doping in AlxGa1−xN grown by gas source molecular beam epitaxy with ammonia and silane. Growth conditions that minimize self-compensation were used to assure Si incorporation at a level of 2 1020 cm−3 for the entire range of compositions investigated, from x=0.56 to 1.0. These conditions resulted in donor concentrations of 1 1019 cm−3 up to x =0.85. Layers of AlxGa1−xN up to x=0.85 show good mobility and low resistivity. In these layers, the activation energy, Ea, of Si stays below 25 meV and Si can be considered a shallow donor. For AlN content above x=0.85 the donor activation energy increases to Ea 250 meV in AlN. The change in donor activation energy correlates with increased incorporation of oxygen and carbon.