Gap state absorption in AlGaN photoconductors and solar-blind photodetectors

AlGaN photoconducting layers and solar blind UV-detectors with high responsivities in a narrow range of photon energies were grown by molecular beam epitaxy on c-plane sapphire substrates. The applicability of photothermal deflection spectroscopy and the spectral photocurrent measurements for absorption studies in III-nitride thin films is investigated. Process dependent variations in direct band-gap energies, Ur-bach's tail widths, bulk and surface defect densities in the films are given as a measure of composition and structural quality of epitaxial layers. The difference of more than one order of magnitude in the photocurrent above the band gap has been measured in back- and top-illuminated UV-photodetector heterostructure demonstrating a functionality of the integrated filter (cut-off energy similar to 4.85 eV). The UV/visible contrast of more than four orders of magnitude has been observed. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.