Photocatalytic Performance Of Two-dimensional Gan Nanomaterials From First-principles Study

The increasing demand for energy due to the intensification of modern industrial technology and the growing problem of environmental pollution have led researchers to develop environmentally friendly clean energy.Hydrogen is recognized as the most ideal clean energy source,and the photocatalytic decomposition of water is an environmentally friendly approach.Compared with solids,two-dimensional materials have many unique properties for photocatalysis,such as porous structure,high specific surface areas,good crystallinity,easier separation of carrier and abundant reaction sites.Gallium nitride?GaN?is a new semiconductor material for the development of microelectronic devices and optoelectronic devices.It called the third generation semiconductor material.It has wide direct band gap,high thermal conductivity,and good chemical stability.Because of the large band gap value of GaN materials,GaN materials not can be directly used as photocatalysts.We need to reduce the band gap value,and widen the range of visible light response,etc.Now the method of extensive research is to study modification by establishing solid-soluble system or establishing heterojunction.In this paper,it will be modified by ion doping to obtain good photocatalytic performance.The method of doping is anion monodoped and anion monodoped,and C atom is used to replace N atom.The codoped anion is C-Ge and C-Sn.In this paper,the geometric structure,electronic structure,defect formation energy,band edge position and optical properties of the doped system are mainly calculated.For the calculation of electronic structure and optical properties,a more accurate calculation method is chosen:hybrid density functional?HSE06?theory.Then the main conclusions of this paper are as follows:1.According to the band structure,the effective band gap value of C atom monodoped GaN nanosheet is:1.84 eV.But it is observed that there is impurity energy level.Combined with the density of states diagram,it is known that this impurity energy level belongs to the unoccupied,and it is easy to form the composite center of photo-generated electron-hole pairs.Thus,it will reduce the carrier concentration and affecting the carrier mobility.The band gap values of C-Ge and C-Sn codoped GaN nanosheets are:2.66 eV and 2.12 eV,respectively.The codoping effectively reduces the band gap value and there is no unoccupied impurity level.2.The defect formation energy of three doping modes has been calculation.The results of indicate that the defect formation energy of monodoping?C?is positive and the C-Ge and C-Sn co-doped is negative,under the condition of rich N.This result shows that C-Ge and C-Sn codoped are easier to achieve than C monodoping.The defect formation energy of C-Ge codoped is minimal.The same defect binding energy also indicates that C-Ge co-doped relatively pure system has the best stability.3.Since the electronic structure of GaN nanosheets of C monodoping is not improved very well.Therefore,we will only calculate the band edge positions of the C-Ge and C-Sn co-doped and pure systems.The calculated results show that the C-Ge and C-Sn co-doped conduction band minimum is higher than the H⁺/H₂ reduction potential,and the valence band maximum is higher than the O₂/H₂O oxidation potential.It indicates that both C-Ge and C-Sn codoped GaN nanosheets are suitable for hydrogen production as Z-type photocatalysts.4.Finally,the optical absorption spectrum of the co-doped system is calculated.The optical absorption curves of C-Ge and C-Sn co-doped systems show obvious red-shift phenomenon.This indicates that C-Ge and C-Sn co-doping increase the range of light response of GaN materials,especially the visible part.C-Sn co-doped system has the widest response range to visible light.