Electrical properties and defect states in undoped high-resistivity GaN films used in high-power rectifiers

The electrical properties and spectra of deep centers in high-resistivity u ndoped GaN samples used to fabricate high-power Schottky diode rectifiers w ith breakdown voltages exceeding 2000 V are reported. It is shown that the Fermi level in such material is pinned by defects with energy levels close to E-c-0.6 eV. Thermally stimulated current measurements revealed the prese nce of unidentified traps with activation energies of 0.3 and 0.7 eV. The i mportant role of hole traps with energy levels E-v + 0.3 eV and E-v + 0.9 e V was confirmed by measurements of temperature quenching of photocurrent an d by photoinduced transient current spectroscopy measurements. Prominent pe rsistent photoconductivity was observed even for temperatures above 300 K. Imaging of the sample using microcathodoluminescence showed the existence o f cellular nonuniformities with characteristic dimensions of the cells of a bout 3 mu m. (C) 2000 American Vacuum Society. [S0734-211X(00)06803-7].