Top- and bottom-illumination of solar-blind AlGaN metal-semiconductor-metal photodetectors

摘要

The spectral performance of solar-blind Al_xGa_(1-x)N based metal-semiconductor-metal ultra-violet photodetectors has been measured for top as well as bottom-illumination at different bias voltages. In the bottom-illumination case the external quantum efficiency spectra can be tuned between a peak or a broad wavelength spectrum by adjusting absorber layer thickness and applied bias voltage. For thin absorber layers the external quantum efficiency is enhanced by a factor of three, reaching 20% quantum efficiency at 20 V bias, compared to the front-illumination case. Results of two-dimensional device simulations are well in agreement with the experimental findings. From these simulations it can be concluded, that the different spectral response for top- and bottom-illumination results from the different overlap of optical carrier generation by absorption and carrier transport by the electric field. Spectra of external quantum efficiency of solar-blind metal-semiconductor-metal photodetectors upon top-illumination (dashed) and bottom-illumination (continuous) at 1V, 5 V, and 20 V bias voltage. The Al_(0.5)Ga_(0.5)N absorber layers of different thickness d_(Abs) were grown on AlN/sapphire templates.