Improvement of n-Type Poly-Si Film Properties by Solid Phase Crystallization Method

Abstract

Polycrystalline silicon (poly-Si) thin films prepared by the solid phase crystallization (SPC) method were investigated for application as photovoltaic materials. To improve the properties of the poly-Si thin film, two methods were developed to control crystallization. One is the partial doping method, in which starting material of a-Si consists of a doped layer and an undoped layer. We have succeeded in controlling nuclei generation using partial doping, and high mobility of 196 cm2/V·s was obtained at a carrier concentration of 1×1018 cm-3. SPC temperature can also be decreased to 500°C. The other is adoption, for the first time, of a textured substrate which exerted effects on the enlargement of grain size in poly-Si thin films prepared by the SPC method. By combining the partial doping method with the textured substrate, an n-type poly-Si thin-film with the grain size of 6 µm was fabricated which showed the Hall mobility of 623 cm2/V·s (n: 3.0\times1015 cm-3). In a solar cell (thickness: 12 µm) applying this film, a conversion efficiency of 6.2% was obtained and a collection efficiency of 50% was achieved at a wavelength of 900 nm.

The control of the film stress of Cat-CVD a-Si films and its impact on explosive crystallization induced by flash lamp annealing

“…A variety of methods have been investigated to obtain thin poly-Si [1][2][3][4][5], and the crystallization of precursor amorphous Si (a-Si) films by post-annealing is one of the most successful approaches to form poly-Si films [1][2][3]. We have so far investigated the utilization of flash lamp annealing (FLA), millisecond-order discharge from Xe lamps, to crystallize precursor a-Si films prepared on glass substrates [6][7][8][9][10][11][12].…”

Mechanism and control of crack generation in glass substrates during crystallization of a-Si Films by flash lamp annealing

“…Polycrystallization of precursor amorphous Si (a-Si) films prepared on low-cost glass substrates is a promising approach to form c-Si films [1][2][3][4][5][6][7], and solar cells with a conversion efficiency of more than 10% have been actually demonstrated when polycrystalline Si (poly-Si) films formed through solid-phase crystallization (SPC) are used [1]. Furnace annealing for the SPC, however, generally requires long duration of around 10 h, which would be a problem in mass-production, and more productive crystallization methods have been desired.…”

Variation of crystallization mechanisms in flash-lamp-irradiated amorphous silicon films

“…Another approach to form thin c-Si is the utilization of thin Si films deposited on lowcost substrates, and a number of researchers have proposed various methods to form thin c-Si films, e.g. crystallization of deposited precursor amorphous Si (a-Si) films by annealing [5][6][7][8], and epitaxial growth of c-Si films on thin large-grain c-Si seed layers [9]. Although high throughput and low damage to low-cost substrates with poor thermal tolerance are necessary for the formation of thin c-Si, most of the methods do not meet these requirements.…”