Study On The Structure And Electronic Properties Of The New Low-dimensional Group ? Nitrides

In the development of semiconductor materials,the third-generation semiconductor is a wide bandgap semiconductor represented mainly by gallium nitride and silicon carbide.For example,the band gap of gallium nitride is 3.4 e V,and the band gap of boron nitride is 5.97 e V.The band gap of aluminum nitride is 6.2 e V.It is the wide band gap characteristics of materials that make this type of semiconductor material play a very important role in optoelectronic devices.At the same time,the advantages of good electrical conductivity and low dielectric constant make it widely used in high-power,high-density integrated electronic devices.Therefore,the research on group ? nitrides has become one of the key research topics in the semiconductor field.Initially,the group ? nitrides existed in a three-dimensional form and were widely used.However,with the continuous development of science and technology,people began to synthesize two-dimensional materials of group ? nitrides.Research has found that low-dimensional materials exhibit different electronic properties and application advantages from those of three-dimensional materials.Therefore,it is necessary to discuss the change law of physical properties of materials after dimensionality reduction.However,experimentally,there are still many limitations in achieving controlled growth of two-dimensional materials,and it is still in its infancy.At this time,theoretical research can play a good role in guiding and exploring.Through theoretical design of different low-dimensional group ? nitride structures,the corresponding electronic properties can be studied,and it can provide knowledge reserves and guidance for experimental synthesis.In this paper,firstly,first-principles methods based on density functional theory are used to study the effects of different structural configurations and applied stresses on the electronic properties of the new low-dimensional group ? nitrides;secondly,for material growth.The experimental phenomenon of introducing dislocation defects is inevitable in the process.The dislocations and grain boundaries of single-layer aluminum nitride in low-dimensional nitrides are simulated and studied,and the influence of the introduction of dislocations and grain boundaries on the electronic properties of materials is studied.Finally,the summary rules provide possible theoretical guidance for the study of low-dimensional nitrides in experiments.The specific research work is as follows:(1)In order to solve the problem of the internal electrostatic field in the wurtzite phase nitride,an effective method is provided,which is to reduce the thickness.The study found that as the thickness decreases,the wurtzite phase transforms to the Haeckelite phase.The Haeckelite configuration is a stable structure and the internal electrostatic field is almost zero,revealing the ground state structure of low-dimensional nitrides.In addition to the energy advantages of two-dimensional Haeckelite aluminum nitride versus wurtzite aluminum nitride,the thickness of the new two-dimensional Haeckelite aluminum nitride can be adjusted to achieve continuous adjustment of the band gap from 3.85 e V to 4.76 e V.It has greatly broadened the application potential of two-dimensional aluminum nitride in optoelectronic devices.(2)Investigate the influence of applied stress on the geometric structure and electronic structure of two-dimensional Haeckelite aluminum nitride.The results show that under the applied strain,the indirect band gap can be transformed to the direct band gap.At the same time,it is found that the two-dimensional Haeckelite phase aluminum nitride exhibits strong anisotropy with external strain.This is because the change in the position of the top of the valence band during the transition from the indirect band gap to the direct band gap of the two-dimensional Haeckelite phase aluminum nitride is controlled by the p orbital of the nitrogen atom.It points out that the introduction of strain is very effective for band gap regulation.(3)To study the influence of dislocations and grain boundaries of single-layer aluminum nitride on the electronic properties of the system.According to experimental phenomena,it is found that dislocation defects will inevitably occur due to the different crystal grain orientations during the growth of the material,which leads to a reduction in the quality of the material and affects the properties of the material.In response to this phenomenon,a variety of single-layer aluminum nitride dislocations and grain boundaries are designed theoretically,and the influence of the types of grain boundaries on electronic properties is discussed.According to the different types of grain boundaries,symmetric grain boundaries and asymmetric grain boundaries are designed respectively.The study found that when the rotation angle is 48.53° in the symmetrical grain boundary,the symmetrical grain boundary is of metallic nature.In the asymmetric grain boundary,when the rotation angle is 44.82°,the asymmetric grain boundary changes from an indirect band gap semiconductor to a direct band gap semiconductor.The results show that by adjusting the rotation angle and changing the grain boundary morphology,the electronic properties of the single-layer aluminum nitride can be controlled.Compared with the grain boundaries that hinder electronic transport in graphene,single-layer aluminum nitride with the introduction of grain boundaries and dislocations will have certain application potential in the fields of electronics and optics.