Theoretical Calculations Of Doping Properties Of(Al)GaN Semiconductor Materials

Due to the direct band gap of gallium nitride(GaN),aluminum nitride(AlN)and related multi-component alloys,the group ?-nitride materials have become the focus of semiconductor research in the past few decades.In addition,Because of gallium nitride's wide bandgap,high electron saturated rate,high thermal conductivity,stable chemical properties and high anti-irradiation properties,many breakthroughs have been made in the preparation of high-power,high-frequency and high-temperature resistant semiconductor devices.However,the point defects and impurities in nitrides often exert a decisive influence on the properties of materials.The micro addition of donor or acceptor impurities can make the material exhibite n or p type,which gives the electronic or optoelectronic devices have different functions.Therefore,it is necessary to study and discuss the properties of doping for characterizing or suppressing irradiation damage and analyzing equipment degradation.With the development of algorithms and the enhancements of computer technology,the accuracy of first-principles calculation in micro-level systems has reached an unprecedented level,which has become a powerful tool for the research of semiconductor materials and devices.At present,the most advanced solid-state calculation is based on the density functional theory and provides detailed information of the atomic structure.In this thesis,I mainly use the density functional theory to carry out the following work around the problems of doping.This work is described in the following sections:1)Theoretical calculation of doping properties in GaN and AlN.Firstly,the basic properties of GaN and AlN are calculated,and the electronic structures of GaN and AlN are analyzed.Due to the natural n-type conductivity in the growth process of nitride materials,the intrinsic defects play a very important role,which is also the reason why p-type doping is difficult,so I also analyze the intrinsically defective behavior of GaN and AlN.In the growth process,the doping of C impurity also affects the properties of the material.I also discuss the doping behavior of C impurity.Through the calculation of hybrid density functional theory,it is revealed why p-type doping is difficult to achieve in ?-nitride group materials.2)Based on the above calculation,the first-principles hybrid density functional simulation of the structure and electronic properties of Be doped acceptors in GaN is carried out.The results show that the Be acceptor has a metastable configuration(SB2-AX),which is very similar to the ground state configuration(SB1-AX).The two configurations have almost the same ionization energy(0.72ev and 0.80ev)and emission peak(1.73ev and 1.71ev),which can explain the anisotropy of the Yellow PL band in the OMDR experiment.The results deepen the understanding of Be doping in GaN and provide guidance for the detection of defects in nitride-based electronic devices and optical devices.3)The first-principles study of strain in Al1-xGaxN epitaxial layer is carried out next.The nonlinear mechanical properties of hexagonal GaN and AlN are calculated at the GGA level.The third-order elastic constants are obtained by the strain-energy method.The bending coefficients and other parameters of disordered epitaxial materials are predicted.The strain energy and internal stress of different gallium-component epitaxial layers on different substrates are analyzed.Especially in the epitaxial structure of AIN substrate,with the increase of gallium content,the influence of nonlinear effects on internal stress is as high as 29.4%.,which fully proves the important influence of the nonlinear mechanical response on semiconductor materials and heterojunction structures.4)Theoretical computational studies of(AlN)5/(GaN)1 ultrathin quantum well(Ga ?-doping)were carried out to investigate the effect of superlattice structure on the electrical and nonlinear optical properties of materials.Based on the density functional theory,the band-structure and polarization optical properties of(AlN)s/(GaN)1 ultra-thin quantum well,(AlN)m/(GAN)n(m+n=6)and(AlN)m/(GAN)1(m=1,3,5,7)are discussed.The special superlattice structure of(AlN)5/(GaN)1 transforms the ?cr in the material from-231.8 meV(AlN)to 202.5 meV,the forward TE-mode polarized light dominates the luminescence mode.Then the effect of Si doping on the electronic structure and optical properties of(AlN)5/(GaN)1 supercell quantum well are discussed.Finally,the effects of the special microstructure(AlN)m/(GaN)n(m+n=6)and(AlN)m/(GaN)1(m=1,3,5,7)on polarization optical properties are further discussed.