Calibration of the WCT-100 photoconductance instrument at low conductance

The WCT-100 photoconductance instrument is used throughout the photovoltaic industry providing a relatively simple and inexpensive means to assess recombination parameters. This paper presents a method to determine its output voltage V-WCT over the conductance range, S = 0.002-20 mS, a range not easily attained by the conventional calibration method. The relationship between V-WCT and S is found to transition from being non-linear to linear at S similar to 1 mS, which equates to the conductance of a 300 gm thick 30 Omega-cm silicon wafer. For samples whose dark conductance is lower than the transition conductance, the non-linear relationship between V-WCT and S must be taken into account to prevent a gross underestimation of recombination rate. The method we describe can equally well be used to investigate the calibration of other photoconductance instruments. It involves the simultaneous measurement of a device's electrical conductance and the instrument's output voltage under a range of steady-state illumination intensities. Copyright (C) 2008 John Wiley & Sons, Ltd.