Wednesday June 29, 2005
Thursday June 30, 2005

"High performance AlGaN/GaN based ultraviolet photodetectors"
Mr. Turgut Tut
Bilkent University

Turgut Tut, Necmi Bıyıklı, İbrahim Kimukin, and Ekmel Özbay AlGaN/GaN based heterojunction solar blind Schottky, p-i-n, and, MSM photodetectors have been fabricated and characterized. With Al0.38Ga0.62N/GaN Schottky photodiodes, low dark current, high responsivity, and fast pulse response were observed. 30 micron diameter devices exhibited leakage current below 3fA under reverse bias up to 12V. True solar-blind operation was ensured with a sharp cut-off around 266nm. Peak responsivity of 147mA/W was measured at 256nm under 20V reverse bias. A visible rejection more than 4 orders of magnitude was achieved. The thermally-limited detectivity of the devices was calculated as1.8x1013cmHz1/2W-1. Temporal pulse response measurements of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1GHz bandwidth. A bandwidth-efficiency product of 2.9GHz was achieved with the AlGaN Schottky photodiodes. With p-i-n photodetectors, we obtained low dark current and high detectivity. Measured dark current was below 3 fA for reverse bias values up to 6 V, and the detectivity of the devices was calculated as 4.9x1014 cm Hz1/ 2W-1. With high Al-content Al0.6Ga0.4N MSM PD’s, we measured very low dark current, high breakdown voltage, and low cut-off wavelength of 255 nm. T. Tut and E. Ozbay are with the Department of Physics, Bilkent University, Bilkent Ankara 06800, Turkey.