Investigating impurities and surface properties in germanium co-doped multi-crystalline silicon: a combined computational and experimental investigation

Directional solidification (DS) method was employed in the production of multi-crystalline silicon (mc-Si) ingot. Extensive research has been conducted to assess the impact of introducing germanium as a co-dopant into the mc-Si ingot. Incorporating germanium into the material was found to enhance both wafer strength and minority carrier lifetime while reducing light-induced degradation (LID) and dislocation density within the ingot. Upon subjecting the prepared samples to chemical etching, distinctive pits resembling worm-like structures were observed, as obtained in the scanning electron microscope image. Further analysis was focused on assessing oxygen and carbon concentrations in the top, middle, and bottom wafers of both central and peripheral bricks. Electron probe microanalysis (EPMA) revealed a notably high germanium concentration in the middle wafer. These experimental findings underscore the favourable properties of germanium-co-doped silicon, particularly its reduced impurity content, which is poised to enhance the efficiency of solar cells. Moreover, a high-resolution optical microscope was employed to visualize and code-map all grain boundaries and twin boundaries present within the samples.