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

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
2
, is illuminated by an incident light chopped at a frequency f
1
, where f
1
and f
2
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