Differential photocurrent method for measurement of the optical-absorption coefficient and the minority-carrier diffusion length in a semiconductor

Abstract

A new method, named DPC (differential-photocurrent), is proposed for measuring the optical-absorption coefficient and the minority-carrier diffusion length in a semiconductor. In the DPC method, a sample photodiode under a reverse bias, which is modulated at a frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , is illuminated by an incident light chopped at a frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> , where f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> are close, and the DPC of the diode is measured. The method is free from limitations due to effects of surface recombination, surface reflectivity, and photon-transmission coefficient of surface layer. The optical-absorption coefficient for an n-type