The thin films of amorphous silicon carbide (a-SiC) have been prepared on fused silica by chemical vapor deposition (CVD) using a gaseous mixture of $SiH_4$, $CH_4$, and $H_2$. In this work, the effects of deposition temperature and the input gas ratio ($CH_4$/$SiH_4$) on the bond structure, the optical band gap, and the resistivity of the deposited a-SiC are investigated.
Raman spectra show that a-SiC deposits have transverse acoustic (TA) mode of SiC, Si-CH band, Si-$CH_3$ band and Si-H band. These experimental results show that the deposition temperature and input gas ratio ($CH_4/SiH_4$) affect the bond structure of the deposited a-SiC.
The optical band gap of chemically vapor deposited a-SiC decreases slightly as the deposition temperature increases from 923 K to 1023 K. But the optical band gap of the deposited a-SiC decreases above the deposition temperature of 1073 K. The reason why the optical band gap decreases above the deposition temperature of 1073 K is believed that the evolution of hydrogen atoms which have been dangled to Si atoms increases the dangling-bond density. It is believed that the increase of the dangling-bond density reduces the optical band gap of the deposited a-SiC.
These experimental results show that the resistivity of the deposited a-SiC increases a little as the deposition temperature increases from 923 K to 1023 K but decreases between the deposition temperature of 1023 K and 1073 K. It is believed that the decrease of the resistivity is due to the decrease of the structure disorder through decreasing the TA mode of SiC. It is observed that the resistivity is a little affected by the input gas ratio ($CH_4$/$SiH_4$).
From these experimental results, it is suggested that the deposition temperature has a great effect on the bond structure, optical band gap and resistivity of the chemically vapor deposited a-SiC. It is also found that the bond structure is closely related to the optical band gap and resistivity of a-SiC deposits.
