The Surface Morphology And Optical Analysis Of Diamond-like Carbon Films Prepared By PECVD

DLC films (Diamond-like carbon films) are amorphous carbon film containing diamond (sp3 bonds) and graphite (sp2 bonds), which has the wearability, the thermostable, the anti-corrosive, high degree of hardness, high electronic resistivity, high transmittance and other unique physical and chemical properties. Generally, the energy gap varies in the range of 1-4eV and the refractive index changes from 1.54 to 2.05 of DLC thin films prepared in different conditions. Because Diamond-like carbon can greatly improve the efficiency of optical electronic transformation, maintain chemical stability in a UV and high-energy particle radiation or under extremely harsh environments when used as protective layer of Si solar cell, DLC films performs a very broad prospects. Plasma chemical vapor deposition has a huge advantage, such as, low deposition temperature, widly optional substrates and large growth area. Therefore, large-scale deposition of excellent surface morphology and optical properties can be achieved hopefully.In this thesis, to study the growth mechanism of DLC films, the films were succesfully prepared on Si and glass substrates by radio frequency plasma enhanced chemical vapor deposition ( RF-PECVD)at room temperature with the CH4 as the carbon source and high purity Ar as the carrier gas by studying the optimization preparation technological conditions. The asymmetry peak of DLC films between 1200cm^-1 and 1700cm^-1 was observed by Raman spectra analysis. From the surface roughness of DLC films, we can see that the surface is smooth and dense.When the RF power increased from100w to120w, the grain size reduced from 8.018 nm to 4.2 nm and the roughness decreased from 2.2nm to 0.9nm, which is theoretically related to the enhanced effect of the plasma bombardment. The analysis of the thickness of DLC films show that the mothod of the PECVD was efficient, plasma density increased with the power increase, and the deposition rate was accelerated on the condition of self-bias rised. It is noted that the reflection spectrum of DLC films prepared on Si substrate has the property of protective reflectional layer. Obviously, the transmission spectrum of DLC films shows that DLC films has certainly increase transmission within the visible area. It was found that the transmission of the DLC films was primarily related to percentage of sp3 bonds. In the case of the proportion of sp3 bonds is high, the optical transmission was excellent, otherwise, the optical transmission was poor. It was also found that the illumination peak of DLC films from the PL spectrum locates at 460nm with of the DLC films analysis by the He-Cd pulse photoexcitation. As a result, the DLC thin-films band gap was calculated to 2.7ev. It is theoretically noted that the light-emitting of DLC films result mainly from the radiative recombination of electron-hole pair of the sp2 clusters. Meanwhile, the experimental study indicated that the DLC films have few sp2 bonds, which is consistent with the Laman spectra analysis.In conclusion, DLC films with the property of anti-reflection and transmission function can be succesfully prepared on Si and glass substrates by radio frequency plasma enhanced chemical vapor deposition ( RF-PECVD)at room temperature, which play an important role in optoelectronic devices, especially for the application of solar photovoltaic devices.