Investigations On Preparation And Properties Of Boron-and Nitrogen-doped CVD Diamond Films

Diamond is a wide-band gap semiconductor with many excellent properties, however , the high resistivity at room temperature hinder its applications especially in the electricity. The radius of boron atom is close to that of carbon, p-type diamond can be easily achieved by boron doping with a comparably shallow accepter level in the band gap. However, the effective n-type diamond is difficulty to obtain in nowadays. So it is interesting to obtain effective p-type and n-type diamond films.In this paper, the boron doped diamond films of different boron content have been prepared by direct coupling Quartz-tube MPCVD. The influences of boron content on the growth and electronic properties of the diamond films were studied. Furthermore, nanodiamond and nitrogen doped nanodiamond films have been deposited by enhancing the CH4 and adding nitrogen content in the reaction gas, we have investigated the role of the CH₄ and nitrogen on the growth and properties of the nanodiamond films.The quality of the diamond films was enhanced through less boron doping in the films. However, as the boron content was further increased, the films quality deteriorate due to large amount of boron radical that suppress the dissociation of the diamond growth radicals. The diamond (111) diffraction intensity increase and the others diffraction intensity decreases as boron doping. The Raman spectra of the films show that the graphite content reduces and the quality of the diamond films were enhanced by adding less boron. The downshift and asymmetry of the intrinsic Raman peak of diamond can be explained by Fano effect. Hall effects show that the as- deposited films were p-type diamond films and the electrical resistivity reached to 10^-3Ω·cm.The crystal size of as-deposited diamond films changed from micro to nano level by enhancing the CH4 content in the reaction gas. The SEM, XRD and Raman spectra show that the nanodiamond films have high quality. On this basic, a few nitrogen is added into the reaction gas and we found that nitrogen has important influence on the growth of diamond films. The adding of nitrogen raised the content of C2 radical that can promote the secondary nucleation of diamond. The non-diamond phase enhance due to the exiting of large mount of CN radical. The nitrogen doped nanodiamond films with an average size of 10 nm from SEM, XRD and Raman Spectrum have been deposited by increasing the nitrogen content, the film was deposited on the single crystal p-type Si and the nanodiamond/p-typeSi heterojunction showed excellent rectifying behavior. These results suggest that the major carriers of the films are electrons, i.e., the nitrogen doped nanodiamond might show n-type characteristic. Compared with the specimen prepared by Ar-rich plasma, ours have a higher turn-on voltage and relatively lower leakage current due to less defect states in the band gap.