The performance of AlGaN solar blind UV photodetectors: responsivity and decay time

The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied. The photodetectors have shown a good spectral responsivity in a narrow spectral range (220 < lambda < 300 nm) and a short time response with the best estimated characteristic time constant of tau similar to 30 ms measured at room temperature. Possible mechanisms responsible for the persistent photoconductivity (PPC) effect in AlxGa1-xN (x = 0.51) are analyzed. A shape of the spectral response as a function of the applied voltage is analyzed in the frameworks of the space-charge limited current model. It has been shown that the main source of PPC is traps above the Fermi level. PPC occurs when the density of free carriers equals the density of the traps. The model attributing PPC to the spatial separation of the photoexcited electrons and holes by the macroscopic potential barrier is not supported by our photocurrent studies. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.