First-principles Study On The Energy Band Properties Of ZnO Doped With Group VI Elements

Group ?-? oxides have potential applications in light-emitting diodes,solar cells,and laser devices due to their wide band gap,direct band gap,and large exciton free energy.Wurtzite Zn O is a new type ?-? group oxide semiconductor material with a band gap of 3.37 e V,an exciton binding energy of up to 60 me V,a low dielectric constant,good photoelectric properties and piezoelectric characteristics environmental protection and low price.Therefore Zn O can be used to manufacture optoelectronic devices and has potential research value in light-emitting devices,high-power electronic devices,and photovoltaic elements.Doping is an essential means to improve the optoelectronic properties of semiconductors and enhance the performance of optoelectronic devices.Therefore,it is necessary to understand the effect of doping on the properties of semiconductors.In this study,the group ? element doped Zn O was used as the research object.The density functional theory?DFT?The CASTEP module in Material Studio software of the one-principle software package performs lattice optimization and atomic position relaxation of intrinsic Zn O and its doping system based on the local density approximation?LDA?exchange-correlation function.The intrinsic Zn O and its based on the lattice constants of the doped system,the band structure was calculated by the LDA+U method.The findings are as follows:1.The O-rich Zn O_1-xSe_x?0?x?0.3125?alloy is studied.The results show that:?1?The lattice constant of the ternary alloy Zn O_1-xSe_x increases with the increase of Se concentration after the substitution of the Se atom by the O atom.The increase is related to the atomic radius of Se being larger than that of O.?2?After the Se atom replaces the O atom position,although its band gap value will decrease,its band gap is still a direct band gap.?3?When the Se composition is not large,the s-s coupling between the Se-4s state and the Zn-4s state is very weak,and the drop in the band gap caused by the bottom shift of the conduction band is small.?4?Adding a small amount of Se atoms to Zn O can introduce localized Se impurity levels above the top of the Zn O valence band.The initial position of the Se impurity level is about 0.76 e V above the top of the Zn O valence band.Due to the strong localization characteristics of the Se impurity level,the valence band top of the Zn O_1-xSe_x alloy is pinned near the initial Se impurity level.When the Se content is sufficiently large,the localization effect of the Se impurity level becomes weak.In this case,the decrease in the band gap can be attributed to the downward shift of the conduction band bottom position and the upward shift of the valence band top position.2.The Zn O_1-xS_x?0?x?0.25?alloy in the O-rich region was studied.The results show that:?1?After the S atom replaces the O atom position because the radius of S^2-is larger than the radius of O^2-,its ternary alloy the lattice constant of Zn O_1-xS_x increases linearly with increasing S content.?2?When the S atom replaces the O atom position,although the band gap of the ternary alloy Zn O_1-xS_x will decrease,it is still a direct band gap.?3?After adding a small amount of S atoms to Zn O,a localized S impurity energy level will be introduced above the top of the Zn O valence band.The initial S impurity energy level is 0.398 e V higher than the Zn O valence band top.The strong localization of the S level causes the valence band top of the Zn O_1-xS_x alloy to be pinned near the initial S impurity level.As the doping concentration increases,the localization effect of the S impurity level gradually weakens.