First Principle Studies On The Surface And Adsorption Properties Of Wurtzite GaN(0001)

As one of the third-generation semiconductor materials,GaN has a series of excellent characteristics.It is a wide bandgap direct bandgap semiconductor with unique electrical,electronic and optical properties.These unique properties make GaN material one of the key materials for high frequency and high power devices.At the same time,GaN is also a very hard material with stable chemical and mechanical properties,with high heat capacity and thermal conductivity.It is a very important material at present.Surface research is of great significance for understanding the atomic structure,material growth,and electrical properties of semiconductor materials.At the same time,the surface has a variety of morphologies.Among them,the step structure is widely present on the GaN surface,which plays an important role in the synthesis of the material and the growth of the surface.In this paper,density functional theory is used to calculate the surface step structure of GaN(0001)and the atomic structure and electronic structure of O2 molecules adsorbed on it.The analysis focuses on explaining the physical mechanism behind it.To ensure the accuracy of the step structure model and calculation,the lattice constants,atomic layer thickness,atomic relaxation layer number and vacuum layer thickness of GaN bulk and surface structure,and the corresponding convergence accuracy were analyzed and tested.For the step structure,the(Ga2,N1)structure that meets the stoichiometric ratio was selected,and its atomic structure and electronic structure were analyzed.The structural optimization causes the Ga atoms on the GaN(0001)surface to alternately relax up and down.The upwardly relaxed Ga atoms appear in the band gap and the downwardly relaxed Ga atoms transfer electrons to the upwardly relaxed Ga atoms.Therefore,electrons exist on the surface of the upwardly relaxed Ga atoms,indicating that the upwardly relaxed Ga atoms are in a surface state.Considering the 17 possible adsorption sites of O2 molecules on the terrace and the edge of the step in the step structure,the calculation of the adsorption energy shows that the O2 molecule is most easily adsorbed at the edge of the lower step of Ga,and is in a dissociated state.O atoms form bonds with Ga atoms at the edges of the upper and lower steps respectively.The O2 molecular bonds at other adsorption sites were not broken.The analysis of the interaction between O2 molecules and surface atoms by energy band structure,state density and charge differential density shows that there is charge transfer and orbital hybridization between O2 molecules and atoms on the GaN surface.