EFFECT OF THE TWIN PLANES IN DENDRITIC WEB SILICON ON ITS ELECTRICAL CHARACTERISTICS.

The authors analyzed dendritic web silicon, using electron-beam-induced current (EBIC), deep-level transient spectroscopy (DLTS), high-resolution transmission electron microscopy, and X-ray topography to investigate its electrical and structural properties. The twin planes in the web and their effect on minority-carrier diffusion length were of particular interest. Measurements were made on as-grown material and on completed solar cells. The starting material and the completed cells were always from the same web strips. For high-resolution electrical measurements, cross-sectional EBIC with Schottky contacts formed on the web cross sectional area was developed. High-efficiency cells flat EBIC linescans were observed across the web cross sections, along with high minority-carrier diffusion lengths, few dislocations and no defect clusters. For low-efficiency cells, EBIC linescans of reduced amplitude were observed near the twin planes, as well as low diffusion lengths, many dislocations and electrically active defect clusters at the twin planes. In both high- and low-efficiency material, DLTS peaks present in the as-grown material disappear on cell processing. The twin planes appear to be gettering planes in some cases, and high-temperature cell processing anneals defects quenched in during web growth.