Persistent photoconductivity and defect levels in n-type AlGaN/GaN heterostructures

Persistent photoconductivity effects have been characterized in n-type Al_0.15Ga_0.85N/GaN heterostructures using both monochromatic light and room light illumination. Time constants of ∼1×10⁴s have been observed, and measurements of photocurrent specta performed using various illumination geometries and techniques have shown that defect levels exist in both the Al_0.15Ga_0.85N and GaN layers. Broad distributions of defect levels with excitation energies lower than the bandgap energies are found in both Al_0.15Ga_0.85N and GaN, and evidence is observed that these levels contribute significantly to the aforementioned 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 heterostructure.