Deep ultraviolet detection dynamics of AlGaN based devices

Abstract

The photoconductive response of AlGaN based UV detectors to 193nm excimer laser radiation is presented. Two devices have been tested: a metal-semiconductor-metal (MSM) planar structure and a Schottky diode. The transient response of the MSM device closely follows the laser pulses, with a photoconductive decay time constant shorter than 3ns. Conversely, the Schottky diode shows a slower photoconductive rise and decay kinetics due to the material series resistance coupled with the junction capacitance. Moreover, a longer time constant tail is also evident in this case with a characteristic time of about 40ns, due to the presence of trap states localized at 0.2–0.3eV from the band edge. The detection dynamics has been evaluated by changing the beam energy density between 2×10−5 and 0.2mJ∕mm2. The signal increases linearly in the case of the MSM device up to 0.001mJ∕mm2, whereas, for a further intensity rise, the response shows a sublinear behavior. On the contrary, the Schottky diode showed a linear trend inside the reduced 2×10−3–1.5×10−2mJ∕mm2 range.