The responsivity of GaN Schottky barrier photodetector (SBPD) as a function of incident wavelength and reverse bias has been studied theoretically. It was found that Schottky barrier (SB) lowering can explain the significant increase in the spectral responsivity as the reverse bias increases. The image force and the occupation of surface defects at the metal/semiconductor interface of the SBPD are the main factors for the SB lowering. The occupation of the surface defects was assumed to depend on the photogenerated current under reverse bias. The SB lowering causes a large leakage current that dominates the spectral responsivity at high reverse applied bias. The good agreement between the calculated and experimentally measured spectral responsivities suggests that the model is valid.
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