Abstract
We have measured optical absorption in Al 0.18GaN/GaN heterostructures, prepared by MOCVD on sapphire substrates, by the constant photocurrent method (CPM) between 300 and 500 K. The constant photocurrent mode is appropriate since the response time decreases when the incident light energy crosses from below to above the bandgap energy. The films were further characterized by temperature-dependent dark conductivity and Hall measurements. We have found exponential band tails exceeding thermal broadening in the absorption spectra below the bandgap energy indicating the presence of disorder and/or deep defects.
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