Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 16: GaN: Bauelemente
HL 16.3: Vortrag
Dienstag, 9. März 2004, 10:45–11:00, H13
Studies on sub-band gap absorption of AlGaN based solar-blind photodetectors — •R. Wagner1, G. Cherkastinin1, V. Lebedev1, A. T. Winzer2, R. Goldhahn2, and O. Ambacher1 — 1Center of Micro- and Nanotechnologies, TU Ilmenau, D-98684 Ilmenau, Germany — 2Institute of Physics, TU Ilmenau, D-98684 Ilmenau, Germany
AlGaN-based UV-detectors with high responsivities in a narrow spectral range were grown by molecular beam epitaxy on sapphire substrates. These devices are based on heterostructure combining three epitaxial AlGaN layers with different alloy composition acting as optical filter, insulator and detector, respectively. Spectrally resolved photocurrent, photothermal deflection spectroscopy and in situ cathodoluminescence have been applied to obtain a sub- and near band gap absorption in AlGaN layers to provide detailed information about defect states in a wide energy range. By optimizing the alloy compositions and thickness of the filter layer, a peak responsivity of up to 35 A/W was achieved over a narrow range of wavelength with a peak position at 276 nm. The rejection of visible light response with respect to the peak responsivity was about 2 orders of magnitude. This type of sensors can be designed to have a highly selective response suitable for UV flame- and bio-sensors. However, a device performance of AlGaN structures is mainly limited by a high density of defects responsible for reduced UV/visible contrast and slow photoresponse. Thus, the detailed knowledge of the defect structure is necessary for the further performance improvements.