Characterization of the common mode rejection ratio of amorphous silicon balanced photodiode

Abstract

In this work we report on the detailed characterization of an amorphous silicon/amorphous silicon carbide balanced photodiode structure suitable for differential photocurrent measurements. The device is a three-terminal structure constituted by two series-connected amorphous silicon p-i-n photodiodes. Two terminals are used to bias the two photodiodes at the same reverse voltage by the readout electronics. The output signal is the current difference between the two diodes, measured at the third terminal with a transimpedance circuit. Several devices have been fabricated with different areas and geometries utilizing four mask-step process. The devices have been characterized by means of common mode rejection ratio (CMRR) measurements as a function of the radiation wavelength and intensity. The CMRR measured under white light illumination has been found to lie around 37 dB in the whole range of investigated radiation intensities. The decrease of the CMRR observed at shorter wavelengths has been ascribed to mismatches and inhomogeneities in the surface and in the p-type window layer of the two hemi-devices. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA