First-principles Study Of Physical Properties Of Group ?-? Nitride Doping Materials

As the third-generation semiconductor materials,AlN,GaN,InN,BN,and their mixed crystals have attracted great interest due to the broad application prospects in the fields of optoelectronics,spintronic,and photovoltaic devices.Currently,the physical properties of materials are regulated by redesigning high-quality materials,such as introducing impurities,defects and applying strain,which have become the main research route of semiconductor materials to create new materials that satisfy various high-performance requirements.Based on first-principles calculations,the crystal doping modes can usually be classified as substitution,embedding or adsorption guest atoms.Here,with ?-? group nitrides as matrix materials,the bulk and surface of the basic phase?wurtzite structure?and the assembled phase of low-density clusters?nanohole structure?of AlN and GaN were doped and modified.The structure stability,phonon and thermodynamic properties,electronic and magnetic properties of the doping systems have been studied systematically as follows:1.Based on the density functional theory?DFT?,the atomic geometry,phonon and thermodynamic properties of Al_xGa_1-xN mixed crystal over the entire Al concentration range?0?x?1?are investigated.The properties are analyzed by using the generalized gradient approximation?GGA?and the local density approximation?LDA?.The optimal doping position of each component is given explicitly.The accurate phonon spectrums of AlGaN mixed crystal under the entire concentration range are shown.The present phonon calculations of the stable structures for Al_xGa_1-xN show that the vibration frequency increases to a higher frequency with the Al content increasing.The Debye temperature depends approximately linearly on the Al content at zero temperature and room temperature.Additionally,composition dependence of the high-frequency dielectric constants,Helmholtz free energy,zero point energy and Specific heat are determined.2.To understand the interaction mechanism for the oxygen adsorption on the AlGaN surface,herein,we built the possible models of oxygen adsorption on the Al_0.25Ga_0.75N?0001?surface.For different oxygen coverage,three kinds of adsorption sites are considered.Then the favorable adsorption sites are characterized by first principles calculations for?2×2?supercell of Al_0.25Ga_0.75N?0001?surface.On basis of the optimal adsorption structures,our calculated results show that all the adsorption processes are exothermic,indicating that the?0001?surface orientation is active towards the adsorption of oxygen.The doping of Al is advantage to the adsorption of O atom.Additionally,the adsorption energy decreases with reducing the oxygen coverages,and the relationship between them is approximately linear.Owing to the oxygen adsorption,the surface states in the fundamental band gap are significantly reduced with respect to the free Al_0.25Ga_0.75N?0001?surface.Moreover,the optical properties on different oxygen coverages are also discussed.3.For the next-generation spintronic nanodevices,it is highly desirable to explore the ferromagnetic?FM?half-metal materials with high Curie temperature?T_C?,wide half-metallic gap,and large magnetic anisotropy energy?MAE?.Here,from density functional theory calculations,we predict two types of such materials in Mn doped III-N low-density cluster-assembled sodalite?SOD?phases.Specifically,SOD-?Al,Mn?N and SOD-?Ga,Mn?N possess robust FM ground state with high T_C temperature of up to 788 K and 633 K,respectively,due to the strong Mn–N exchange interaction.Both of their magnetic moments are calculated to be 4?_B per formula unit.Interestingly,they have large half-metal direct band gaps(1.70 eV and1.33 eV for SOD-?Al,Mn?N and SOD-?Ga,Mn?N,respectively.The spin-flip scattering during spin transportation can be effectively prevented,guaranteeing the application of half-metallicity at ambient temperature.Moreover,the MAEs of SOD-?Al,Mn?N and SOD-?Ga,Mn?N are-0.56 and-0.53 meV per Mn atom,respectively,and are about two orders of magnitude larger than those of some traditional magnetic materials.Our findings highlight that the FM systems of SOD-?Al,Mn?N and SOD-?Ga,Mn?N are the promising materials for the applications of spintronics.