Structural characteristics of RF- and VHF-deposited nanocrystalline silicon films for solar cell application

Abstract

Nanocrystalline silicon films have been deposited using RF and VHF (54.24 MHz) plasma-enhanced chemical vapor deposition (PECVD) methods. The effects of plasma excitation frequency, plasma power density, chamber pressure, hydrogen dilution of silane and total gas flow-rates on the structural properties of nanosilicon films have been investigated. For all films prepared under different conditions, grain size varied in the range 5–14.4 nm and crystalline volume fraction varied in the range 21–86%. Films with low microstructure factor have been developed successfully using a 54.24-MHz plasma excitation frequency at high total gas flow-rate and optimum power–pressure. Single junction cells have been fabricated using the nanocrystalline silicon films with different crystallinity.

Keywords:

• a-Si:H
• crystal structure
• FTIR
• grain size
• HRTEM
• microstructure
• nanostructures
• Raman spectroscopy