Preparation Of High-quality Cubic Boron Nitride Thin Films By RF Magnetron Sputtering And Their Semiconducting Properties

Cubic boron nitride(c-BN)is a synthetic ultra-wide band gap semiconductor material with a band gap of 6.1-6.4eV.It has excellent physical and chemical properties and can be doped both into n-type or p-type.It has great potential of applications in versatile fields,particularly as high temperature and high power electronic semiconducting devices.In addition,c-BN exhibits super hardness,small dielectric constant,small parasitic capacitance,high working temperature,high energy particle radiation resistance,corrosion resistance,etc.,second only to diamond,and the high breakdown voltage,making it more suitable for working in high temperature,strong radiation and other harsh environment.So far,due to the limitation in the growth process and the lattice mismatch,the preparation of high quality,large-area c-BN film remains challenging.Besides,the accumulation of stress in c-BN thin films inevitably during the preparation process often leads to delamination or cracks of the films,resulting in their future applications elusive.Thus,in this thesis,we focus on the growth of high-quality c-BN thin film by RF magnetron sputtering method,the improvement of film stability by stress release,as well as their semiconducting properties.The main research contents of this thesis include:(1)Growth of high-quality,phase pure c-BN films by optimizing synthesis parameters,such as working gas,negative substrate bias,temperature,and substrate surface in magnetron sputtering deposition.On basis of the previous work,the nitrogen flow and negative bias are mainly considered.As the nitrogen flow increases,the film surface becomes dense and smooth,with improved crystallinity.With the increase of the negative bias voltage,the film surface becomes continuous and smooth without visible holes,tips and cracks.When the negative bias voltage is about-100 V,c-BN begins to nucleate and grow.In addition,at the same growth parameters,when grown on the surface of a h-BN seed layer,pure h-BN thin films will be obtained;whilst,when grown on Si(100)surface,c-BN and h-BN layered-mixed thin films will be obtained.More importantly,when grown on the surface of a c-BN seed layer,a100% pure c-BN film will be obtained.(2)Improvement of the stability by reducing internal stress of c-BN thin films.In view of the problem that the high negative bias voltage will cause the accumulation of internal stress and consequently the surface cracking,we attempt to adopt a two-step method to solve the problem,that is,on the basis of obtaining the c-BN nucleation surface first,in the second step we continue growing the film by reducing the negative bias voltage to 0 V.Unfortunately,pure h-BN films were obtained after the second step,which indicates that the negative bias voltage window still needs to be further explored.Furthermore,post-annealing is also proposed to release the accumulated stress in the film.The results show that with the annealing temperature rising from700 ? to 900 ?,the infrared characteristic peak of c-BN moves to the lower wave number,indicating that the internal stress of the film decreases.(3)Impact of annealing on the semiconducting properties of c-BN thin films.UV-Vis,Hall and I-V results clearly show that the band gap of c-BN thin films decreases with the increase of annealing temperature.The film is p type,and the mobility of the 800 ? annealed c-BN film is significantly improved.The prepared pn junction exhibits obvious rectifying properties and the reverse leakage current of 700 ?annealed c-BN film is reduced after annealing.The present work demonstrate the growth of high-quality and phase-pure c-BN thin films by RF magnetron sputtering method and the improvement of the film stability and their corresponding semiconducting properties by post-annealing treatment.Therefore,the present work provides the possibilities for c-BN thin films applied as high temperature and high power semiconducting devices.