First-principles Investigation Of Electronic Structure And Optical Properties Of Wurtzite ZnO_1-xX_x?X=S,Se,Te? Alloy And The In-doping In ZnO

Semiconductor materials occupy an important position in modern times.ZnO,is the third generation semiconductor material,has attracted people's attention and become a hot topic in the field of frontier during researches of recent years due to various advantages such as wide band gap,high exciton binding energy,low cost and the like.ZnO in the near ultraviolet band and huge development potential,is a kind of candidate material of ultraviolet light emitting devices with high efficiency and low threshold violet semiconductor lasers.ZnO is a natural n type semiconductor material.At present,in order to prepare ZnO thin film devices with high performance,the key step is to realize the control of ZnO band gap.The experimental results show that ZnO can effectively control the band gap by alloy made by doping the element.Because of the defects of oxygen vacancies and zinc interstitial,the natural ZnO is a kind of polar semiconductor material,which is characterized by the conductivity of n type.Therefore,it is easy to realize the n type doping of ZnO.The p type acceptor doping of ZnO,however,has been a key problem that has not been solved very well.At present,the commonly used p doping elements are mainly family I and V elements.Relevant researches show that,the crystal structure of ZnO alloy material,electrical and optical properties can be changed by doping Cd,Ca,Mg and other different elements,and the ZnO emission wavelength covers from blue to purple so that ZnO can be used in blue and ultraviolet laser and light emitting diode devices.This paper adopts the first principles method based on density functional theory?DFT?to study systematically the electronic structure and optical properties of wurtzite ZnO_1-xX_x?X=S,Se,Te?alloy and the n type doping of ZnO.First of all,in order to ensure the reliability of the calculation,we calculate the electronic structures of the intrinsic ZnO to optimize the structure by the AM05 XC function and revise the underestimation of the band gap by LDA-1/2 method.Compared with other theoretical calculations and experimental values,our calculation results are true and credible so as to determine the relevant parameters for the following calculation.Secondly,the paper makes ZnO_1-xX_x?X=S,Se,Te?alloy by doping different concentrations of S,Se,Te with ZnO,studies its the relationship among the lattice parameters,band gap,total energy,and supercell volume with composition x in theoptoelectronics field energy band engineering and calculates in detail the optical properties of the ZnOS alloy.The results show that the lattice parameters,total energy and super cell volume of ZnO_1-xX_x alloy increase with the increase of X concentration,while the band gap presents a bending effect.All the optical coefficients of ZnOS alloy show a red shift with the increase of X concentration.Thirdly,we choose the ZnOS alloy with the same doping concentration,and make the theoretical calculation of the different properties of the four kinds of doped S elements?uniform,cluster,chain,combination?.The results show that the band gap,the bending parameter and the valence band width are sensitive to the distribution of S atoms.In the ZnOS alloy,there may be a considerable number of short Zn-S short chains and small clusters,the conduction band of the alloy is not localized,and the valence band is strongly localized around the short Zn-S chains and small Zn-S clusters of several atoms.Finally,the defect formation energies of In doped ZnO are calculated.The results show that the defect transition energy of the In doped ZnO is ED = 0.692,and the difference between the defect transition energy and the conduction band bottom is 0.105 eV,which is the donor ionization energy and is much lower than the band gap,Eg = 0.797 eV.The ZnO crystals are susceptible to ionization at room temperature,so In doping can be reduced to the shallow donor level.After substituting Zn,In atoms introduce the impurity level near the bottom of the conduction band.