Top‐ and bottom‐illumination of solar‐blind AlGaN metal–semiconductor–metal photodetectors

Abstract

The spectral performance of solar‐blind AlxGa1–xN 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 1 V, 5 V, and 20 V bias voltage. The Al0.5Ga0.5N absorber layers of different thickness dAbs were grown on AlN/sapphire templates.