Opto-electrical characterization of electrically active point defects in Al_xGa_1-xN

Different techniques including admittance spectroscopy, noise spectroscopy and photocurrent measurements have been applied to Al_xGa _1-xN materials grown by metal-organic chemical vapour deposition to investigate their electrical properties. A continuous band of shallow donors with ionization energies ranging from 50 to 110 meV which contribute to the residual conductivity of Al_xGa_1-xN alloys is observed. We also identify a deep centre with optical ionization energy of 1.2 eV which controls the slow buildup of the photocurrent when the materials are illuminated with sub-bandgap photon energy. This centre also induces persistent photocurrent in the material. In the light of this finding we discuss DX-like defects, which may contribute to the slow relaxation phenomena in AlGaN related structures.