Fabrication of silicon thin films with defects below detection limit of electron spin resonance for solar cells by high-speed zone-melting crystallization of amorphous silicon

Ihara, Manabu; Yokoyama, Shuhei; Yokoyama, Chiaki; Izumi, Koichi; Komiyama, Hiroshi
December 2001
Applied Physics Letters;12/3/2001, Vol. 79 Issue 23, p3809
Academic Journal
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 SiO[sub 2] films. The Si films were 0.3–2.0 μm thick, the top SiO[sub 2] films were 0.35–1.5 μm thick, and the bottom SiO[sub 2] 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. © 2001 American Institute of Physics.


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