Investigation On Single Crystal Diamond Grown By MPCVD

Diamond is not only a kind of gem,but also a special material with unique physical,chemical and optical properties.Because of its well-known high hardness,high strength,high conductivity,low thermal expansion coefficient,chemical inertness,excellent optical transparency and semiconductor performance,diamond has attracted extensive research interest in the world.With the development of synthesis technology,the preparation of diamond single crystal becomes possible,so the application of diamond becomes more and more extensive.In addition to the traditional application fields such as jewelry decoration,precision cutting,abrasive tools and so on,the application of diamond materials in the fields of microelectronic mechanical system,acoustic devices,semiconductor devices,biomedical,quantum communication and so on is increasingly concerned by the academics and industry.Especially,owing to its excellent semiconductor properties,such as wide band gap,high thermal conductivity,high breakdown voltage,high carrier mobility and strong radiation resistance,diamond is known as the "ultimate semiconductor",and has wide application prospects in the fields of deep UV detector,particle detector,high power,high voltage and high frequency electronic devices.However,compared with other mature materials,there are still many problems in the preparation of diamond materials,especially single crystal diamond(SCD).With the extensive application of diamond,the first issue is the preparation of the large size,high rate,and high quality SCD.Among the many preparation methods,microwave plasma chemical vapor deposition(MPCVD)is the most mature nowadays,and it is also the only method to obtain high-quality large-area single-crystal diamond materials.In this,thesis,low surface roughness,high temperature and high pressure(HTHP)diamond is selected as the substrate material of the homoepitaxial diamond.MPCVD method is used to grow the diamond single crystal.The growth conditions such as off-axis angle of substrate,pressure at growth chamber,growth temperature and different vapor species partial pressure are optimized to obtain high-quality and high-rate SCD films.High surface quality of HTHP substrate is the primary condition for homoepitaxial epitaxy.The surface morphology of the diamond after laser cutting,the changes of the surface state during polishing,the surface damage and quality of the polished diamond were analyzed.After the two-step of mechanical polishing and chemical mechanical polishing,the carbonized layer and damaged layer on the diamond surface brought by laser cutting were effectively removed,and the surface roughness reached 0.764nm.In this work,the influence of off-axis angles of substrates on the diamond growth were investigated.It was found that using a substrate with off-axis angle can effectively suppress the nucleation of the pyramid diamond island during the epitaxial process.It was found that the growth rate and the doping efficiency of nitrogen for the epitaxial diamond were influenced by the growth temperature.Increasing the chamber pressure can effectively increase the growth rate and improve the quality of the epitaxial diamond.The addition of oxygen improves the quality of the epitaxial diamond,but at the same time decreases the growth rate.As the oxygen concentration increases,the growth rate decreases linearly.In this work,the(100)lattice plane bending of diamond single crystal was studied by high-resolution X-ray diffraction.It is found that the lattice plane bending of the HTHP substrate is anisotropic.The lattice plane is not spherical.First,the lattice plane bending of SCD has the hereditability,i.e.,it depends mainly on the substrate itself.The lattice plane bending of SCD becomes more severe with increasing lattice plane bending of the substrate and this type of lattice plane bending cannot be recovered.The SCD growth experiments show that growth parameters such as temperature,growth time and lattice plane bending of the substrate affect the lattice plane bending of SCD.And the lattice plane bending increases at high temperature and with increasing growth time.Finally,to understand the mechanism of lattice plane bending,we investigated the substrate-surface temperature distribution as a function of lattice plane bending of SCD(CVD).It is believed that an uneven temperature distribution on the substrate surface is the main cause of the CVD diamond lattice-plane bending.