Deep ultraviolet detection dynamics of AlGaN based devices

摘要

The photoconductive response of AlGaN based UV detectors to 193 nm 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 3 ns. 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 40 ns, due to the presence of trap states localized at 0.2-0.3 eV from the band edge. The detection dynamics has been evaluated by changing the beam energy density between 2 x 10~(-5) and 0.2 mJ/mm~2. The signal increases linearly in the case of the MSM device up to 0.001 mJ/mm~2, 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 x 10~(-3)-1.5 x 10~(-2) mJ/mm~2 range.