Defect density of crystalline Si films fabricated by high-speed zone melting crystallization for solar cells

The defect density of crystalline Si films fabricated by high-speed zone melting crystallization (ZMC) of amorphous Si (a-Si) and by high-speed zone melting re-crystallization (ZMR) of polycrystalline Si (poly-Si) was investigated by using electron spin resonance (ESR). The crystal defect density of the sandwich-structured a-Si ZMC films (SiO/sub 2/ film/Si film/SiO/sub 2/ film) was lower than that of the sandwich-structured poly-Si ZMR films for a lower-heater temperature range of 1470/spl deg/C to 1570/spl deg/C and for an upper-heater scan-speed range of 0.7-4.5 mm/s. The defect density of the bulk a-Si ZMC films was below the detection limit of ESR, even at high scan speed of 7.0 mm/s. Therefore, a-Si ZMC films can be used to fabricate solar cells that have an efficiency higher than those fabricated by current processes involving poly-Si ZMR films.