Structural Analysis of Nanocrystalline Silicon Prepared by Hot-wire Chemical Vapor Deposition on Polymer Substrates

摘要

Nanocrystalline silicon (nc-Si:H) films were deposited by hot-wire chemical vapor deposition (HWCVD) directly onto Corning glass and polyimide (Kapton E) substrates. The effect of silane concentration (in hydrogen carrier gas) on film crystallinity and conductivity were studied for a constant substrate growth temperature of 220 °C. Raman spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy (XTEM) showed that nc-Si:H (grain-size 20-65 nm) was observed for silane concentrations below 5.8 %. Similar to previous reports, closer inspection using XTEM found that there was an initial growth of an amorphous interfacial layer which then crystallized into a randomly-oriented polycrystalline material after 10 – 100 nm of growth. However, unlike previous reports, there was no detectable difference in the structure or conductivity for films grown on the two types of substrates. In both cases, the dark conductivity decreased with increasing silane concentration while the photo-conductivity was uniform for all films at values between 2 and 4×10~-5 S/cm.