Effect Of Transition Metals (Sc, Ti, V, Cr And Mn) Doping On Electronic Structure And Optical Properties Of CdS

CdS has been widely used in photovoltaic,photocatalyst and piezoelectric devices due to its direct optical band-gap(2.42 eV at room temperature),low resistivity,high absorption coefficient,high conductivity,high electron affinity and high chemical stability.CdS is the main carrier of dilute magnetic semiconductor,and is widely used in the field of dilute magnetic semiconductors such as ultra-sensitive magnetic field sensors,magneto-optical and high-speed computing memories.How to improve the required characteristics of CdS-based semiconductor materials has attracted much attention.The effects of transition metals(Sc,Ti,V,Cr,and Mn)doping at different distances on the structural,electronic,optical,and magnetic properties of wurtzite CdS are systematically studied by VASP 5.4.4 package in this paper.The results show that:1.The volume of CdS is slightly reduced by doping,but doping does not cause lattice distortion,and does not change the wurtzite structure of CdS.The doped systems in this paper are easy to form and more stable than the pure CdS.It is also found that the next nearest-neighbor doping is more stable than other distances,while the single-doping is less stable.2.The doping does not destroy the semiconductor characteristics of the material.All doped systems are direct band-gap semiconductors,and the band-gaps gradually decreasing with the sequence of Sc,Ti,V,Cr,and Mn.In each transition metal doped system,the band-gap of the nearest-neighbor doped system is smaller than others.It is also found that the carrier concentration gradually increasing with the order of Sc to Mn-doping,and all doped systems are degenerate semiconductors.Combined with the effective mass of the carrier,it is found that the doping can improve the conductivity of CdS and also improve the photocatalytic performance of the material,especially the Mn-doping has a significant improvement.3.The Sc,Ti,V,Cr,and Mn multi-doped systems can improve the visible light absorption coefficient of CdS in the energy regions less than 2.15 eV,2.56 eV,2.45 eV,2.38 eV,and 0 eV.However,the increase is very small,Mn-doping has little increase and red shift,and the absorption strength decreases with the order of Ti>V>Sc>Cr>Mn.On the contrary,single-doping can significantly increase the light absorption of CdS,and the red shift is obvious.The absorption strength increases with the order of Ti<Sc<V<Cr<Mn.It shows that the single-doping is the best choice to improve the light absorption of CdS materials,and the single-doped with Mn is the best.4.It is found that the system is antiferromagnetic when the nearest-neighbor doping.As the doping distance increases,the system is ferromagnetic.It is also found that the total magnetic moment of each ferromagnetic system increases with the order of Sc to Mn-doping,and the spin polarization of Cr-doped system is 100%.The estimated Curie temperature shows that the Cr and Mn-doping can achieve room temperature ferromagnetic properties,especially Cr-doping.