Bulk minority carrier lifetimes and doping of silicon bricks from photoluminescence intensity ratios

Abstract

Two methods for spatially resolved measurement of the bulk minority carrier lifetime on the side faces of block cast silicon bricks, both based on photoluminescence imaging, are presented. The first method uses a single photoluminescence image which is normalized for variations in the background doping density. The second method is based on the measurement of the ratio of two photoluminescence images taken with different spectral filters in front of the CCD camera. This second method is advantageous over the first method since it is not dependent on an absolute measurement of the luminescence intensity and does not require a separate resistivity measurement. It is further demonstrated, that the measurement of an intensity ratio image and comparison of the latter with an individual luminescence image also allow obtaining the doping density gradient within silicon bricks. This paper presents an in-depth analysis of the underlying models, demonstrates experimental results and discusses the calibration and uncertainties of the techniques. Practical limitations and dependencies on various experimental parameters are discussed.