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HL: Fachverband Halbleiterphysik

HL 65: GaN-based Devices

HL 65.6: Vortrag

Freitag, 26. März 2010, 11:45–12:00, H15

Electrical and Optical Characteristics of GaN based MSM Photodetectors — •Martin Martens¹, Jessica Schlegel¹, Patrick Vogt¹, Frank Brunner², Richard Lossy², Joachim Würfl², Markus Weyers², and Michael Kneissl^1,2 — ¹Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, EW 6-1, 10623 Berlin — ²Ferdinand-Braun-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin

GaN metal-semiconductor-metal (MSM) structures are attractive candidates for ultraviolet (UV) photodetectors because of their fabrication simplicity and their potentially high quantum efficiency, high UV/VIS contrast and high speed. We have characterized MSM UV photodetectors fabricated on semi-insulating GaN by photocurrent spectroscopy and current-voltage (I-V) measurements. The responsivity spectra show a sharp cut-off at 365 nm according to the GaN band gap and high response at shorter wavelengths. Under UV-VIS illumination we measured photocurrents up to 1 mA depending on the applied bias. These high currents indicate an internal gain mechanism which was investigated by photocurrent measurements for different bias and light intensities. After switching off the light the photocurrent decays slowly indicating a persistent photoconductivity (PPC) effect. Therefore the dark I-V characteristics were measured after the samples had been kept in the dark for several hours. Under these conditions the dark current is in the range of 10 nA at 50 V. Subsequent I-V measurements show a degradation in the I-V characteristics suggesting a trap-related effect to cause this behaviour.