First-Principles Calculation And Experimental Investigation Of Silicon Substrate/Iridium/Epitaxial Diamond

Because of its excellent physical and chemical properties,diamond can be applied in various high-tech fields.Single crystal diamond has attracted much attention due to its complete structure,high purity and low defect density.In order to realize the application of electronic devices,large-size and high-quality single crystal diamond wafers are needed.Homoepitaxy and heteroepitaxy are two different approaches towards that goal,whose difference lies in the substrates used for diamond growth.Homoepitaxy relies on diamond single crystal wafer prepared by high temperature and high pressure(HTHP)method as the substrates,while heteroepitaxy requires the growth on non-diamond materials.Choosing a suitable substrate is the first step of heteroepitaxial growth of diamond.It is generally believed that the diamond grown on Ir(100)has the highest growth quality.However,the explanation of this phenomenon and the integrated description of diamond epitaxial growth process are not available.In addition,Ir(100)films still need to grow on other substrates.Considering some theoretical and technical factors,such as the expansion of the substrate area,and the matching of thermal expansion coefficient,it is necessary to design the structure of the substrate and understand the interface interaction and adhesive ability between the layers of the substrate.In this paper,the principle and process of heteroepitaxial growth of diamond on iridium substrate are studied from the above aspects,which can be divided into two parts: simulation and experiment.The simulation part mainly applies the first principles calculation,using the CASTEP program(Materials Studio 2017)based on the density functional theory(DFT),and in some parts,molecular dynamics module Forcite was used to describe some growth kinetics processes.The experimental part mainly includes the preparation of substrate and heteroepitaxial nucleation and growth of diamond.The factors considered in the design of diamond growth substrate are given first,including theoretical and technical factors,so as to design a Si(100)/ TiN(100)/MgO(100)/ Ir(100)substrate,whose structure is suitable for diamond heteroepitaxial growth.The growth process of Ir(100)substrate on MgO(100)substrate is simulated,the forming energy of the growth process is calculated,which was shown in two aspects,one-step formation energy and step-by-step formation energy,and the effects of temperature and growth rate on the growth quality are considered.The growth mode is layer-island growth mode,and the quality of Ir(100)will be improved by increasing deposition rate properly.In order to expand the area of diamond heteroepitaxial substrate,Si can be used as the bottom substrate.Therefore,the interaction process between Si / TiN,Si / TiN / MgO films is involved.In this paper,the interconnection and chemical bonding between these substrates are also described,and the benefits of TiN transition layer is explained.Then,the behavior of C atom on Ir(100)substrate is studied from the perspective of energy from two models of adsorption and desorption,and compared with the interaction and energy change between C atom and Ni,Cu and other substrates,so as to explain the uniqueness of Ir substrate.The diamond heteroepitaxial substrate is also evaluate from the perspective of feasibility and realization.The results of calculations shows that,the structure of C atoms over the Ir substrate is stable.If C atoms precipitate from the sub-surface of the Ir substrate,there is a metastable transition state near the surface of the sub-surface.If C atoms are implanted into the sub-surface of the Ir substrate,they will stay in the metastable position when the concentration of C atoms is low.If the concentration of C atoms is increased,C atoms will eventually precipitate and stay over the Ir surface because it is the stable configuration.The dissolution-precipitation process can be carried out continuously,and it is conducive to the formation of the initial diamond nuclei,and provides energy for the subtle adjustment of the position and orientation of the primary diamond nuclei,so that they can gather and grow,and achieve the similar orientation.Diamond growth is the interaction between various particles and substrate in the growth chamber.The dynamic process of diamond growth is simulated in this paper.In the process of diamond nucleation,it is necessary to increase the nucleation density by applying bias voltage.The reason is explained in this paper.It is considered that the main mechanism of this process is the shallow implantation of C atoms into the sub-surface of Ir substrate.Based on this,the range of bias voltage is calculated,which is in good agreement with the experimental results.When the concentration of C atom increases,the precipitation process and nucleation process are explained,and the chemical bond between Ir(100)/ diamond interface is analyzed.In the aspect of diamond growth,the energy and configuration changes of diamond in the growth process of Ir(100)substrate are simulated.It is considered that the concentration of carbon source should be controlled in the growth process,so that the size of crystals and gaps between nuclei are kept equal,which is conducive to the subsequent connection of nuclei.At the same time,when the orientation uniformity of the formed nuclei is good,that is,the angle between the grains is small,the oriented attachment growth can be achieved.In the last chapter,Ir(100)thin films with high quality and smooth surface of atomic level were grown on MgO single crystal by electron beam evaporation.Diamond nucleation and growth were carried out by microwave plasma assisted chemical vapor deposition.In addition,Si / TiN / MgO layers were prepared by pulsed laser deposition,which made it possible to enlarge the size of the substrate.The theory of the synergy between the technical parameters of the process is explained.In the process of diamond growth,the formation and aggregation of nuclei,the connection of grain boundaries and other processes can be observed,which well support the simulation results,so as to give a complete description of the heteroepitaxial growth process of diamond.Finally,the concept of epitaxial reversibility is proposed,and Ir(100)thin film is epitaxially grown on diamond substrate,which provides a research basis for subsequent heteroepitaxial assisted homogeneous nucleation,substrate patterning and other applications.