Temperature Dependence Of Electronic Structures And Optical Properties Of SiC Using First Principal

Optical properties of semiconductors are one of the most important physicalproperties for semiconductors. As temperature increases, their properties would changemore or less. However, we need optical devices that could work normally at rapidlychanging environment such as wide temperature region. There are many shortages suchas high cost, errors in experimental research, but there is not in simulation. We studytemperature dependence of optical properties based on density function theory with thepurpose of found out calculation method and microscopic mechanism of temperaturedependence of optical properties theoretically in this thesis. We take Silicon Carbide forexample to study band structures and optical properties with increasing temperature inorder to verify the feasibility of this calculation method and provide theoreticalguidance for applying silicon carbide to some extreme conditions.We introduce the research status of silicon carbide and temperature dependence ofoptical properties of materials (both in domestic and aboard), and analyze advantagesand disadvantages of their studies in Chapter one. All these studies not only introducemeasurements of macroscopic dielectric function at different temperature but also a firstprincipal calculation of temperature dependence of dielectric function. At the end of thischapter, we list the research contents of our thesis.In Chapter two, we introduce different models of studying optical dielectricfunction and analyzed advantages and disadvantages of these models in order to lead tomodern theoretical model (for example ab initio calculation). Compared with abovemacroscopic models, modern theoretical model has many advantages. Moreover, wesimply interpret the dependence relationship between optical dielectric function andfrequency and K-K relationship connecting real part and imaginary part of dielectricfunction.In Chapter three, we simply interpret quantum mechanics and take an emphasis onthe elements of electronic band structure influenced by temperature, which can begeneralized lattice thermal expansions, electron-phonon interactions, phonon-phononinteractions and exciton effects. Electron-phonon interactions and phonon-phononinteractions are indirect processes of lattice vibration, and exciton effects are theplasmon of electron transition. We divide optical response regions into visible-ultraviolet region and infrared region and point out main elements of optical response indifferent response regions based on the responding mechanism between light andmatter.We introduce detailed investigation of temperature dependence of opticalproperties of silicon carbide in Chapter four. First of all, cutoff energy, K space sampling and lattice parameter are performed for convergence analysis which is thebasic calculation parameters for calculation of Silicon Carbide. We calculate bandstructure, density of state taking lattice thermal expansion and electron-phononinteraction at increasing temperature. At last, the imaginary part of dielectric function atparticular temperature is calculated based on band structure at this temperature and realpart can be derived from K-K relationship. Then, we compare our calculation resultswith experimental results of references and indicate general tendency and microscopicmechanism of optical properties with increasing temperature. Furthermore, we predictedthe application of Silion Carbide in high temperature areas and indicated the probabilityof application for other materials.