Chemical Vapor Growth Of High Quality Hexagonal Boron Nitride Films Assisted By Catalysts

Hexagonal boron nitride (hBN) is a wide band gap semiconductor with direct band gap. Its band gap is about 6eV. hBN is of high promise in applications of UV light emission and high frequency electronic devices.In this study, hBN films were prepared by microwave plasma chemical vapor deposition (CVD), and the effects of catalysts on the CVD growth of hBN films was investigated. The purpose of this study is to obtain high-quality hBN films by introducing catalysts during CVD process. The reactive gas system is the mixture of He-N2-BF3-H2 and the substrates are (100)-oriented monocrystal silicon wafers. The effects of catalyst nature, fabrication process of the catalysts, and the CVD parameters on the quality of the hBN films were investigated. The luminescence properties of the catalytically grown hBN films were also measured.Firstly, selection on the catalysts was carried out, and the fabrication process of the catalyst films was carefully investigated. Based on the published literatures and the related thermodynamic data, Ni, Mo and Ni-Mo alloy were selected as the catalysts for growing the high-quality hBN films. It was found that Mo, and Ni-Mo have obvious catalyzing effects on the growth of hBN films. The catalyst films were fabricated by magnetron sputtering on Si substrates. Subsequent annealing was conducted for improving the quality of the catalyst films, and the catalyst films became more uniform in surface morphology with crystal size increased. The crystallinity of hBN films was characterized mainly by Raman spectroscopy. Obvious narrowing of the Raman peaks was observed for the catalytically grown hBN films comparing with that grown directly on Si substrates. Further improvement in crystallinity was obtained by subsequent annealing for the catalytically grown hBN films. The annealed catalysts exhibits more obvious catalyzing effects on the hBN growth.The effects of the CVD parameters mainly reactive pressure and bias voltage on the quality of the hBN films were also investigated. It was found that the growth rate is strongly dependant on the reactive pressure. The growth rate is very low at very low pressure. The quality of the deposited films will decrease at very high pressure. So the optimization working pressure is 6 kPa. The addition of bias voltage will cause the quality of the film to decrease because of the ions bombardment.Inaddition, photoluminescence properties were measured and an emission peak located at 379 nm was observed, corresponding to the energy of 3.28 eV, which can be ascribed to the deep level defect emission. This peak narrows with increasing annealing time, suggesting the decrease of defect and improvement of the crystallinity.