“Shadow effect” photodetector with linear output voltage vs light intensity

Abstract

A novel concept for a simple, cost effective, readily integrable with Si electronics and self-powered photodetector is presented. The device consists of a semitransparent Au film deposited on an n-type Si substrate with contacts on the Au layer. The operation of the device relies on the recently demonstrated “shadow effect.” The device is shown to consist of back-to-back Schottky diodes with a built-in parallel resistance caused by the Au layer. Shadowing half of the device area under illumination causes anisotropy in the diodes' behavior creating a measurable open circuit voltage and a short circuit current. The presence of the built-in parallel resistance, along with a large series resistance, causes the open circuit voltage to have a linear term with respect to illumination power, in addition to the logarithmic term normally present in Schottky solar cells. We demonstrate that under certain combinations of series and parallel resistances the open circuit voltage of the device is linear with respect to illumination power for a range between 50 mW/cm2 (0.5 sun) and 0.5 mW/cm2 (0.005 sun). This allows the device to be used as a photodetector operated as a self-powered voltage source, instead of a current source which is the case with most photodetectors operated in the photovoltaic mode.