Optical characterization of wide band gap amorphous semiconductors (a-Si :C : H): Effect of hydrogen dilution

The effect of hydrogen dilution on the optical properties of a wide band ga p amorphous semiconductor (a-Si:C:H) was investigated. The samples were pre pared by glow discharge decomposition of tetramethylsilane and were charact erized primarily by optical techniques: spectroscopic ellipsometry, Raman s cattering, infrared absorption, spectrophotometry, and UV photoluminescence . The deposition rate decreased with hydrogen dilution, while the silicon t o carbon ratio remained constant with the addition of hydrogen. The optical band gap of this material increased as the hydrogen flow rate increased. I nfrared absorption studies show that the concentration of hydrogen which is bonded to carbon decreases systematically upon hydrogen dilution. Hydrogen dilution appears to reduce the size and concentration of sp(2) bonded carb on clusters, possibly caused by the etching of sp(2) clusters by atomic hyd rogen. The result was also supported by the shift of the Raman G peak posit ion to a lower wave number region. Room temperature photoluminescence in th e visible spectrum was observed with UV excitation. (C) 2001 American Insti tute of Physics.