Surface passivation of pyramidally and isotropically textured c-Si by PECVD SiNx and a-Si:H And: Laser processing of crystalline silicon solar cells

Yimao Wan and Daniel Walter (Centre for Sustainable Energy Systems, ANU)

SOLAR SEMINAR SERIES

DATE: 2013-05-08
TIME: 10:00:00 - 11:00:00
LOCATION: Ian Ross Seminar Room
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ABSTRACT:
Yimao Wan: We report on the surface passivation of inverted pyramidally textured (intex) and isotextured (isotex) crystalline silicon (c-Si) wafers by amorphous silicon nitride (SiNx) and amorphous silicon (a-Si:H). Three SiNx films and one a-Si:H are examined by varying precursor gas flow ratio (NH3:SiH4) in a microwave/radio-frequency plasma enhanced chemical vapour deposition reactor. The surface recombination velocity (SRV) is found to depend on the properties of the passivating layers and the silicon surface morphology. When passivated by N-rich SiNx (n = 1.85), SRV increases significantly as the surface becomes less planar (i.e., for a higher proportion of {111} surface area for intex and a higher texture feature for isotex). When passivated by Si-rich SiNx (n = 2.0 and 2.5), the dependence of SRV on surface morphology tends to be weak. When passivated by a-Si:H, the recombination behaves differently at the intex and isotex surfaces. Whereas SRV of intex decreases strongly with an increase in the {111} proportion of surface area, SRV of isotex is constant with texture depth. Possible causes for the behaviour of intex are (i) there are twice the dangling bonds at a {100} surface than at the {111} surface; and (ii) epitaxial growth at a-Si:H/c-Si interface, which is known to be detrimental to the surface passivation of {100} rather than {111} surfaces. Annealing of the samples suggests the second cause is more likely to be responsible for the behaviour of intex samples.

BIO:
Yimao Wan received the B.E. degree from the Nanyang Technological University, Singapore, in 2004. From 2004 to 2007, he was with STMicroelectronics, Singapore and from 2007 to 2010, he was with Peregrine Semiconductor, Sydney, NSW, Australia; in both organisations he was a semiconductor manufacturing process engineer. Since 2010, he has pursed the PhD degree in engineering at the Australian National University, Canberra, Australia. His research focuses on the characterisation of silicon Nitride layers for silicon solar cell passivation.