Shallow and deep defects in AlxGa1−xN structures

We report electrical characterization of AlxGa1−xN materials grown by MOCVD. The techniques used in this study were admittance spectroscopy and photocurrent measurements. We identify a continuum of shallow donors with ionization energies ranging from 50 to 110 meV in AlxGa1−xN alloys with values of the Al mole fraction x=0.1 and 0.3. Investigations of the photocurrent buildup kinetics allow identification of a deep center with optical ionization energy of 1.2 eV. This center controls the buildup of the photocurrent when the materials are illuminated with sub-bandgap photon energy. In the light of this finding we discuss the broad spectrum of DX-like defects that may contribute to the persistent photocurrent and the collapse in the drain current observed in AlGaN-related structures.