Silicon (Si) thin films with very-low defect density for solar cells were fabricated by using high-speed (0.7-4.5 mm/s) zone-melting crystallization (ZMC) of amorphous-silicon (a-Si) thin films, resulting in films that had defects below the detection limit of electron spin resonance (ESR). In this letter, poly-crystalline silicon (poly-Si) films for zone-melting recrystallization (ZMR) and a-Si films for ZMC were each sandwiched between two SiO2 films. The Si films were 0.3-2.0 μm thick, the top SiO2 films were 0.35-1.5 μm thick, and the bottom SiO2 films were 0.18-1.2 μm thick. The a-Si ZMC films had higher crystal quality than did the poly-Si ZMR films. Over 90% of the grains in the a-Si ZMC films had preferred (100) orientation when the films were formed at scan speeds 0.7-4.5 mm/s. Transmission electron microscopy (TEM) revealed that neither distinct grain boundaries nor defects were visible in the a-Si ZMC films within the 9-μm-diam observation field. The a-Si ZMC films fabricated from the a-Si films with the thickness smaller than 1 μm had no voids. Such a low defect density indicates that silicon thin-film solar cells with high efficiency can be fabricated by using such very-low defect density silicon thin films.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)