PERSISTENT PHOTOCONDUCTIVITY AND DEFECT LEVELS IN N-TYPE ALGAN GAN HETEROSTRUCTURES/

Persistent photoconductivity effects have been characterized in n-type Al0.15Ga0.85N/GaN heterostructures using both monochromatic light and room light illumination. Time constants of similar to 1 x 10(4) s hav e been observed, and measurements of photocurrent specta performed usi ng various illumination geometries and techniques have shown that defe ct levels exist rn both the Al0.15Ga0.85N and GaN layers. Broad distri butions of defect levels with excitation energies lower than the bandg ap energies are found in both Al0.15Ga0.85N and GaN, and evidence is o bserved that these levels contribute significantly to the aforemention ed persistent photoconductivity effects. The photocurrent spectra also reveal the presence of a level with an excitation energy of' 3.36 eV that contributes to the persistent photoconductivity in the heterostru cture. (C) 1988 American Institute of Physics.