Difference in silicon photodiode response between collimated and divergent beams

Abstract

A theoretical model, whose validity was confirmed experimentally, has been used to investigate the polarization properties of silicon photodiodes as functions of the angle of incidence with wavelengths ranging from 10 nm to 800 nm. From this, spectral differences in the responses of silicon photodiodes between a collimated beam and a beam with angle divergence are derived. The calculation shows that divergent beams (both isotropic and Gaussian beams) usually give lower responses than those for a collimated beam except in a limited spectral region (approximately 120 nm to 220 nm for a Si photodiode coated with a SiO2 layer of thickness 27 nm). The decrease in response of the Si photodiode with 27 nm SiO2 for the isotropic divergent beam with half apex angle of the beam cone of 60° reaches a maximum of 14 % at a wavelength of 44 nm and the increase reaches a maximum of 7.5 % at 163 nm. Similar results for a Si photodiode coated with an 8 nm oxide layer and a divergent beam with Gaussian angular distribution were also obtained.