Controlling a three dimensional electron slab of graded Al_xGa_1−xN

Polarization induced degenerate n-type doping with electron concentrations up to ∼10²⁰cm⁻³ is achieved in graded Al_xGa_1−xN layers (x: 0% → 37%) grown on unintentionally doped and on n-doped GaN:Si buffer/reservoir layers by metal organic vapor phase epitaxy. High resolution x-ray diffraction, transmission electron microscopy, and electron dispersive x-ray spectroscopy confirm the gradient in the composition of the Al_xGa_1−xN layers, while Hall effect studies reveal the formation of a three dimensional electron slab, whose conductivity can be adjusted through the GaN(:Si) buffer/reservoir.