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Published online by Cambridge University Press: 10 February 2011
Deep levels in high resistivity layers of AlGaN grown by MOCVD on sapphire were studied by means of dark current and photocurrent versus temperature measurements and by photoinduced current relaxation spectroscopy (PICTS). Strong temperature quenching of photocurrent was observed and explained by the presence of hole traps with energies 0.2 eV, 0.3 eV and 0.35 eV for films with correspondingly 5%, 15% and 25% of Al. Two hole traps with activation energies of 0.27–0.35 eV and 0.85–1.05 eV depending on composition were detected in PICTS spectra. It is suggested that the former traps are the same as observed in temperature quenching of photocurrent while the latter traps are related to the yellow luminescence band in AlGaN. The photocurrent decay is shown to have a complex form with a rapid decrease followed by a long tail associated with detrapping of holes. It is argued that, at room temperature, the ∼1 eV hole traps are mainly responsible for the amplitude of the tail.