Theoretical Calculation Of Wide Bandgap Nitride Semiconductor Doped Electronic Structure And Epitaxial Growth

Group III-V nitrides（Ga N,AlN,etc.）are the representative materials of the third-generation semiconductors.They have wide band gap,high saturated electron drift rate,high breakdown electric field,fast electronic peak speed,good thermal stability and corrosion resistance.They are widely used in the field of high power,high voltage and other optoelectronic devices.This paper is divided into two parts.Firstly,the doping system of Ga N material is systematically studied by first-principles calculation,and a series of dopable elements are predicted and analyzed to provide reference data for experiments.Then,the growth process of homogeneous epitaxy deposition of aluminum nitride（AlN）was simulated by molecular dynamics simulation.The quality of the deposited crystals was observed by changing the growth temperature,N:Al flux ratio and substrate inclination to explore better growth conditions.1.Impurity doping is one of the important means to adjust the physical properties of intrinsic semiconductors.This study combines data mining with first principles to predict a series of potential doping elements in Ga N material by using Shannon radius and probability model.Thirty-six dopable elements were predicted using Shannon radius and replacement probability as criteria for screening dopable elements.The structural stability,electronic structure and optical properties of these doped structures were systematically studied by first-principles calculations.Among them,14 impurities can form defects with less than 3e V and are less difficult to dope.They are n-type systems:O_N,Zr_Ga,Ti_Ga,Si_Ga,F_N,Ge_Ga,Nb_Ga,S_N,Se_N,p-type systems:Be_Ga,Mg_Ga,Ca_Ga,Zn_Ga,Mn_Ga.In these potential doping systems,changes in the electronic structure of the doping system can be divided into two types depending on whether or not the impurity level is introduced.The doping systems of Ti_Ga,Nb_Ga,F_N,and Mn_Ga introduce significant impurity levels into the band gap.The electrons directly participate in the carrier transition.For other doping systems,no significant impurity levels are introduced in the band gap.Compared with the undoped Ga N material,the electronic density of state of the doped system is significantly higher at the minimum conduction band.These results may provide an effective theoretical reference for screening suitable Ga N doping for experiments.2.As a third generation semiconductor material,aluminum nitride（AlN）thin film is not only widely used in many fields such as medicine and Optoelectronics due to its excellent performance,but also can be used as buffer layer epitaxy material to alleviate lattice mismatch to fabricate high performance AlN-based devices.Therefore,how to grow high-quality AlN material film has become the focus of research.In this study,the growth of AlN on C-plane（0001）substrate by homogeneous epitaxy was studied using molecular dynamics simulation.The effects of growth temperature,N:Al flux ratio and substrate inclination were simulated and studied.The changes of surface morphology and dislocation of AlN thin films are discussed in detail.The results show that the crystallinity and surface morphology of the deposits are improved with the increase of temperature.When the temperature reaches around 2000 K,the crystal quality is the best and the dislocation density is lower.When the N:Al ratio is 1.0,the crystal quality is relatively high.Low N:Al ratio will cause Ga atoms to cluster.High N:Al ratio will limit the mobility of Al adsorbed atoms and lead to blockage of Al atomic sites and decrease the deposition quality.With the increase of the oblique cut angle of the substrate,the growth quality of the crystal is increasing and the dislocation density is decreasing.However,the higher oblique angle may cause the stress to increase,which may affect the surface morphology and increase the surface roughness.These results provide some practical growth parameters for the homogeneous epithelial growth of AlN and have important reference value.