The dependence of Hall mobility and carrier concentration in GaN epilayers on light illumination was examined. It was found that Hall mobility and electron concentration both increased after illumination with red laser (632.8 nm) and green laser (530 nm). However, no changes in Hall mobility and carrier concentration were found, if IR-laser (850 nm) was used. The results reveal that deep-level defects were excited and hence extra carriers were generated by light illumination. The influence is more pronounced for thinner films. These observations indicate that donor-like defect-related states were located 1.48 to 2.33 eV below the conduction band edge.
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