Research On The Structure And Optical Properties Of Hydrogenated Amorphous Carbon And Silicon Carbide Films

Hydrogenated amorphous carbon(a-C:H)and hydrogenated amorphous silicon carbide(a-Si C_x:H)film have gained a lot of attention of the researchers due to its high hardness,low friction coefficient,excellent chemical stability,high visible light transmittance,stability room-temperature photoluminescence(PL)properties as well as adjustable refractive index and optical band gap.A lot of research shows that the structure and optical properties of the a-C:H and a-Si C_x:H films can be controlled by growth process parameters of the films,hence the research on the influence of growth process parameters on the structure and optical properties of the films is mainly focus,and also the key to promote the application of a-C:H and a-Si C_x:H films in the industry.The a-C:H and a-Si C_x:H films were prepared by plasma enhanced chemical vapor deposition system(PECVD).The structural and optical properties of the films were studied by changing the radio-frequency(RF)power,silane flow rate and substrate temperature in turn.In addition,a possible PL emission mechanism originated from the sp~2C domain is also discussed by studying the relationship between thin film structure and optical properties.The research on the structure and optical properties of a-C:H thin films shows that:As the RF power increases,hydrogen content in a-C:H film first decreases and then slightly increases.The sp~2carbon content gradually increases and the film tended to be graphitized with increasing RF power.In addition,with the increase of RF power,optical band gap of the film decreases from 1.4 e V to 1.8 e V,which leads to a gradual redshift of photoluminescence.The research on the structure and optical properties of a-Si C_x:H film shows that the film is a graphite-like sp~2C clusters embedded into C-C/C-Si amorphous matrix.The chemical composition and microstructure of the films can be controlled by the growth process parameters.In addition,the a-Si C_x:H films embedded with carbon nanoclusters and graphite nanocrystals are obtained by controlling the growth parameters of the films.This research also found that the sp~2C clusters in the film have a great influence on the transmission,absorption spectra and PL properties of the film.The research details are as follows:(1)With the increase of silane flow,the silicon content increases,and the content of sp~2C first increases and then decreases,which also leads to a series of decrease of optical band gap and red shift of PL.(2)As the substrate temperature increases,Si,C-Si and sp~3C content in the a-Si C_x:H film first increases and then decreases.At the same time,approximately spherical sp~2C nanoclusters are observed in the a-Si C_x:H film.The carbon nanoclusters grow with increasing temperature.Finally,the carbon nanoclusters are identified as onion-like structures with multiple graphite layers.The graphite layer spacing vary in 3.9-4.1?.(3)With the increase of RF power,the growth rate of the a-Si C_x:H film gradually increases,sp~2/sp~3increases,Si and C-Si contents decrease.The average size of sp~2C clusters increases while the density of sp~2C clusters decreases with increasing RF power.As the RF power increases,the PL spectra are gradually red shift,the color of PL spectra changes from light blue to light yellow.