The Theoretical Study And Design Of Doped ZnO Nano Film Broad-band Gap One-dimensional Photonic Crystal In The Visible Light Wavelength

The zinc oxide itself has a band gap of 3.37 eV and an exciton binding energy as much as 60 meV,and is rich in raw materials and low in cost.Also,ZnO film has good transparency,piezoelectricity,photoelectricity,gas sensitivity,pressure sensitivity,which makes it widely used in all walks of life.Nano-sized zinc oxide is a new type of high-functionality fine product,which has important applications in many fields because of its nano-effects.In recent years,the research on the transparent antireflection film of ZnO has been fully developed in various fields,especially the doping of different elements.However,most of them are concentrated on the macroscopic scale.Considering the difficulty in preparation of nano-films,the application of zinc oxide nano-films is limited.To understand the properties of zinc oxide nano-films and even doped films,in this paper,the calculation of density functional theory is mainly applied by controlling the size of the zinc oxide film in the nanometer thickness,and exploring effects of different element doping on the properties of thin films from the atomic level,which hopes to provide theoretical guidance and prediction for the development of zinc oxide thin films on optoelectronic devices.Then,the structure is chosen to explore the change of its nature by using the smaller photonic crystal structure.That is,a one-dimensional photonic crystal multi-layer film structure constructed by combining a B-doped zinc oxide nano-film and silicon is designed in combination with the Translight software based on the transmission matrix method.Meanwhile,the influence of different parameter settings on the band gap is explored through changes in the parameters(number of period layers,unit cell parameters,and fill ratio).The calculation results show that:(1)The 4-layer structure of zinc oxide(0001)nanostructure film is a cycle.Through the optimization analysis of the surface structure from 4 to 24 layers,the surface energy has reached a sufficiently stable state when the number of layers reaches 12 layers.Based on the relationship among absorption(A),reflectance(R),and transmittance(T),namely,R+A+T=1,it can be concluded that the transmittance is inversely proportional to reflectance and absorption coefficient.While the absorption and reflectance of ZnO nanofilms are relatively lower than that of bulk.Therefore,the transmittance of the film is higher than that of the bulk,especially for the 12-layer structure.(2)After doping different elements(Al,B,Si,and Ti)into 12-layer structures,the data are collected and analyzed in the same way.It is well found that the doping of different elements on the optical properties is not the same.Firstly,the bingding energy formed by four different elements replacing zinc is all negative,indicating that the replacement system can be stable.Secondly,in the visible range,Al and B-doped ZnO nano-films can reduce the absorption coefficient of the material,and have the potential to be used as antireflection films.In general,the transmission coefficient of zinc oxide nano-film doped with boron is the largest,and its conductivity is better than that of bulk structure,which completely meets the requirements of transparent conductive antireflection film.(3)The B-doped ZnO nano-film and silicon were combined into a one-dimensional photonic crystal multilayer film structure,and the effects of different unit cell parameters,number of periodic layers,and filling ratio on the band gap are analyzed.The results show that,in terms of the number of periodic layers,the reflectance of the band gap has almost reached 100% when it is greater than or equal to eight.Therefore,we choose the number of cycles N=8 in the subsequent calculation.When other parameters are the same,the increase of the cell parameters causes the width of the photonic bandgap to significantly widen,and the position of its center wavelength shifts to the long-wavelength direction.In order to make the band gap cover the visible light band as much as possible,the cell parameters are selected to be 100 nm.As the fill ratio increases,the center wavelength of the photonic band gap also shifts toward the long wavelength,and the width of the band gap undergoes a change that it first broadens and then narrows.Therefore,the appropriate fill ratio is choosed in the case of ensuring the width of the band gap and the band,so choosing 0.4 is enough.The band gaps obtained under these parameters are broadened to cover almost the entire visible light band(421.65-728.40 nm).