Polycrystalline silicon thin films for photovoltaics

[摘要] Selective nucleation and solid phase epitaxy offers a low temperature methodto fabricate large grain, polycrystalline silicon on foreign substrates. Undopedand highly doped silicon films were nucleated with nickel or indium andannealed at 600°C. Indium nucleated crystallization proceeded by conventionalsolid phase epitaxy. Undoped silicon had grain sizes of 1-2 µm. With doping, although there was enhancement of the growth rate, the grain size did notincrease, since the incubation time correspondingly decreased. The exceptionwas the phosphorus-doped silicon that had a maximum grain size of 10 µm.In nickel-nucleated samples, the amorphous silicon layer fully crystallizedbefore the onset of random nucleation, achieving grain sizes on order of tens ofmicrons. Within each grain, however, were many low angle, sub-grainboundaries that came from the needle-like crystal growth. Epitaxy on theselayers resulted in strained columnar crystals with dislocations.Positron annihilation spectroscopy (PAS) was used to study vacancies in solidphase crystallized silicon in four doping cases: undoped, B-doped, P-doped, andP and B-doped. Oxygen-vacancy complexes were seen in all samples andphosphorus-vacancy complexes in the P- and P and B-doped samples. Progressiveetchback of a subset of the samples was achieved, and a defect concentration onorder of 10^(15) cm^(-3) was estimated for all samples.

[发布机构] University:California Institute of Technology;Department:Engineering and Applied Science

[关键词] Applied Physics