Network structure of a-SiO:H layers fabricated by plasma-enhanced chemical vapor deposition: Comparison with a-SiC:H layers

Abstract For hydrogenated amorphous silicon oxide (a-SiO:H) layers applied to crystalline Si heterojunction solar cells, we have studied the correlations between the dielectric function and local bonding states using spectroscopic ellipsometry and high-sensitivity infrared spectroscopy. In particular, systematic characterizations have been made on both a-SiO:H and hydrogenated amorphous silicon carbide (a-SiC:H) layers prepared at similar conditions. In a-Si 1− x O x :H and a-Si 1− x C x :H layers, the increase in the alloy content x leads to the significant reduction in the amplitude of the dielectric functions due to microvoid formation. The infrared spectra reveal that the local bondings in the a-SiO:H are dominated by SiH 2 and SiH m (O 4−m ) (m ≤ 2) at high x , whereas the local bonding states of the a-SiC:H alloy can be interpreted as a mixture of SiH 2 and CH n (n = 2, 3). The amplitude of the a-SiO:H dielectric functions shows a clear relationship with a total amount of SiH m (O 4−m ) in the network, indicating that the significant microvoid formation in a-SiO:H layers is most likely triggered by the generation of SiH 2 (O 2 ) and SiH(O 3 ). Our results indicate that, compared with the C atom, the O atom increases the band gap of a-Si:H more effectively while suppressing the H incorporation in the amorphous network.