APPARATUS FOR DIGITAL ELECTRON-BEAM-INDUCED CURRENT IMAGING

A new electron-beam-induced current (EBIC) apparatus for studying char ge carrier recombination at extended defects in semiconductors is desc ribed. It employs computer-automated measurement and control equipment to acquire high resolution beam-induced current images using a conven tional scanning electron microscope. The EBIC images typically contain a matrix of 512 x 512 digitally measured points, each point of which is a result of multiple averaging. The images can be displayed on a wo rkstation monitor and image processing using commercially available so ftware packages can be performed. All the components of the system and software, except the data acquisition software routines, are readily available as off-the-shelf items. A method of calibrating the equipmen t in terms of quantum efficiency by scanning well-characterized solar cells of known material and physical properties was developed. As an e xample of an application, a modified quantitative analysis method is a pplied to the problem of precipitates that act as point recombination centers distributed through a Czochralski silicon solar cell. The anal ysis, based on non-linear curve fitting, results in a characterization of the strength of the charge carrier recombination at a given defect and the depth of the defect below the sample surface.