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HIGH-QUALITY POLYCRYSTALLINE SILICON THIN FILMS PREPARED BY SOLID PHASE CRYSTALLIZATION (SPC) METHOD T. MATSUYAMA, T. BABA, M. TANAKA, S. TSUDA, H. NISHIWAKI, S. NAKANO, H. HANAFUSA*, AND Y. KUWANO* Functional Materials Research Center, Sanyo Electric Co., Ltd., 1-18-13, Hashiridani, Hirakata, Osaka 573, Japan *R&D Headquarters, Sanyo Electric Co., Ltd., 1-18-13, Hashiridani, Hirakata, Osaka 573, Japan ABSTRACT The relationship between the grain size of poly-Si after SPC and the structure of a-Si before SPC was studied. The structure of a-Si was characterized by TA/TO: the Raman intensity ratio of the Transverse Acoustic (TA) like band and the Transverse Optical (TO) like band. A good positive correlation between the grain size and TA/lTO was revealed for the first time. The nucleation and growth kinetics were speculated by using a thermodynamic model. The grain size could be enlarged up to 6 p m by applying textured substrates to a-Si with a large structural disorder. This film was applied to the active layer of solar cells, and a collection efficiency of 51% at 900 nm was obtained. INTRODUCTION Solar cells are now gathering much attention as a clean energy source. However, higher conversion efficiency and lower cost are necessary for their practical use. In order to achieve both high conversion efficiency and low cost, an amorphous silicon (a-Si)/thin polycrystalline silicon (poly-Si) tandem structure is promising[I]. Several methods for fabricating thin poly-Si have been proposed, such as a liquid phase process[2], a vapour phase process[3], a solid phase crystallization[4], and a laser recrystallization process[5]. We have been studying the solid phase crystallization (SPC) method from a-Si because it offers several prominent features, as follows. (1) A simple and low-cost process (2) A relatively low temperature process (3) Easy enlargement of the cell size We have developed several techniques to increase the grain size, such as textured substrates and a partial doping technique[6], and the maximum electron Hall mobility of 623 cm 2 fV's was achieved at an electron concentration of 3.0 X 1015 cm-3 by combining these techniques. This film has been applied to the active layer of thin poly-Si solar cells on metal substrates, and a conversion efficiency of 6.2% with a size of 4 mm 2 has been obtained. The aim of this study is to investigate what kind of a-Si is suitable for SPC in order to further improve the quality of thin poly-Si films. This paper will discuss the relationship between the structure of a-Si and the property of thin poly-Si made by SPC. The nucleation and the growth kinetics were also speculated by a thermodynamic model. Finally, we applied thin poly-Si films to the active layer of solar cells. EXPERIMENTAL The starting materials, a-Si, were deposited by a glow discharge of Sill4 or Si2 H6 gas on flat or textured substrates. The distance between top and bottom in the textured substrate is about 10/1 m. a-Si films with various structures were made by changing deposition conditions such as pressure