Grain Boundary Structures and Properties in Polycrystalline Silicon

ABSTRACTThe method of preparation of polycrystalline silicon can have a strong influence on the types and distributions of grain boundaries, and thereby influence the electrical properties of devices made from such materials. Examples of methods employed in the preparation of polycrystalline silicon for solar cell applications include directional solidification (Czochralski pulling and various casting techniques), ribbon growth techniques (ribbon-to-ribbon, edgedefined film-fed growth, low-angle silicon sheet growth, edge supported pulling, silicon-on-ceramic), chemical and physical vapor deposition (CVD and PVD) on silicon and foreign substrates, recrystallization techniques (laser, electron beam), and others such as graphoepitaxy and electrodeposition. This paper reviews the important morphological features such as grain size and defect structures of the various polycrystalline silicon materials and the influence of growth parameters on these features. The effects of grain boundaries on the electrical and photovoltaic properties of various polycrystalline silicon materials will also be discussed.