The Preparation Of Nanocrystalline Diamond Films By Electron Assisted Chemical Vapor Deposition (EACVD) And The Researches On The Photo-electric Properties

In this work,positive bias technology,that is,electron assistance chemical vapor deposition,was applied to deposit nanocrystalline diamond films on polished surface ofα-SiC ceramics and(100)Si wafer substrates.The effects of technological parameters on the films deposition were studied.They concluded gas pressure change with positive bias,nucleation enhanced by positive bias and positive bias applied successively with deposition of the diamond films.The films structure,the films properties and their relation were characterized and analyzed by Raman spectroscopy,X-ray diffraction,field emission scanning electron microscopy,high resolution transmission electron microscopy,atomic force microscopy,Hall effective, I-V characteristic curves,photoluminescence spectroscopy and ellipsometry spectroscopy.The results show,when positive bias was applied from 0A to 10A bias current at 1kPa gas pressure,nucleation and growth were accelerated notably by electron bombardment on singular faces and vicinal faces.That is,first,with electron bombardment H desorptions speeded up,more dangling bonds were produced and adsorption and bonding of CH groups were increased on surface,therefore, nucleation rate increase remarkably.Surfaces of embryos and nucleus often appeared (111) facet;Secondly,when another embryos and nucleus were formed again on the surfaces of steps which had been produced previously,the film surfaces appeared various orientation faces,and the secondary nucleation rates increased notably; Thirdly,when dangling bonds increased further with electron bombardment,the effect of H on stability of diamond structure was reduced.When bias current 6A was applied at 1kPa gas pressure to enhance nucleation on the polished surface of the (100) Si wafer andα-SiC ceramics,electron bombardment produced more(110) steps on the diamond(111) facets.More dangling bonds on the edge of the steps increased remarkably nucleation rate.However,the dangling bond directions agreed with the ones on(100) faces,so the steps with the dangling bonds became suitable nucleation sites which can be used to grow(100) oriented diamond films.Therefore, nucleation rate of(100) oriented growth was increased tremendously by these dangling bonds.Under the condition of 4kPa gas pressure,(100) oriented diamond film can grow on these nucleation sites.There are many(0001) vicinal faces and steps on the polished surface ofα-SiC ceramics,which aid in increasing growth rate on(111) diamond face.So,applying positive bias successively leads to stronger(111) texture of the diamond films onα-SiC ceramics substrates and stronger(110) texture of the diamond films on(100) Si wafer substrates.When bias current 8A was applied successively at 1kPa gas pressure with deposition of the films,surfaces appeared various orientation embryos and steps,and the second nucleation rate increased notably.So,the surface roughness of the nanocrystalline diamond films can reach to lowest value 11nm(scan size:2μm×2μm );the grain size can reach to smallest value 18nm.Hall effective measurement show,when positive bias was applied successively with deposition,the nanocrystalline films deposited exhibited stronger p type semiconductor characterization,hole concentration reached to 10 ¹⁴ cm^-2 carrier migration rate reached to 150cm²v^-1s^-1,bulk resistance rate reached to 10 ³Î©cm. The dangling bonds in vacancy and dislocation,which were produced by electron bombardment,resulted in the stronger p type semiconductor characterization of the films.Heterojunction between the nanocrystalline films and low resistance n type Si wafer substrate has obvious rectification characteristic showed in I-V curve.Without applying positive bias,bulk resistance of the nanocrystalline films deposited can reach to 10 ⁸Ωcm.Ellipsometry spectroscopy measurement show,when the nanocrystalline diamond films were deposited without biasing,the films had an index of refraction of 2.33 which was lower than that of natural diamond,and coefficient of extinction was close to zero.When the nanocrystalline diamond films were deposited with positive bias applied successively,the index of refraction of the films increased to 2.50 which was higher than that of natural diamond,meanwhile the coefficient of extinction of the films increased.Photoluminescence spectroscopy measurement show,when positive bias was applied successively with deposition,the nanocrystalline diamond films exhibited a stronger blue photoluminescence peak at 470nm wave length;but the photoluminescence peak of the films deposited without applying positive bias was very weak.The dangling bonds in vacancy and dislocation,which were produced by electron bombardment,resulted in blue photoluminescence peak of the films.