The Effects Of The Intrinsic Defects On The Structural,Electronic,Optical And Magnetic Properties Of CdSe

Cadmium selenide?CdSe?has become one of the most widely used semiconductor materials because of its excellent photoelectric properties.In this paper,the formation energy,electronic structure,magnetic and optical properties of intrinsic defects of CdSe bulk and monolayer(Cd vacancy,Se vacancy,inverse substitution Cd _See and Se_Cd)were firstly studied,by the method of the plane-wave pseudo potential under the density functional theory,in the GGA+U condition.Here are the results:?1?In contrast to the defects V_Se,Cd_Se and Se_Cd,it is found that the V_Cd defect in bulk CdSe under Se-rich conditions is the easiest to form,this is consistent with the experiments;while under Cd-rich conditions,the V_Se defect is the easiest to form both in bulk and monolayer CdSe.?2?With the present GGA+U calculations,the reasonable direct band gaps for the pure bulk and monolayer CdSe are 1.7 and 2.3 eV,respectively.These different intrinsic defects do not change the nature of the direct band gap of the bulk or monolayer CdSe.However,these different intrinsic defects make the corresponding band gap have a more or less increase or decrease;and almost all defects will introduce the impurity energy levels into the band gap,these could be responsible for the changes of some optical properties.And the impurity levels come from the 4p orbital of Se atoms.?3?In particular,the V_Cd defect can induce the nearest two Se atoms to producethe similar magnetic moment?around 1?B?in the bulk or monolayer CdSe,while the anti-site defect Cd_See as well as other intrinsic defects can't induce any magnetic momentusing the GGA+U calculations.Yet both electronic and magnetic properties in the bulk and monolayer CdSe with the V_Cd defect are inflfluenced by the Hubbard U value of the Se 4 p orbital.If the Hubbard U value is set to zero,then there are no any magnetic moments for the bulk or monolayer CdSe supercell with any intrinsic defect.?4?The absorption edge of all kinds of intrinsic defects slightly moves towards the lower infrared direction.For the bulk and monolayer,the intrinsic defects will affect the absorption coefficient and the utilization of sunlight.