Carrier-mediated ferromagnetism in Mn(II)-doped ZnTe thin films and their optical properties: A first-principles study

We have investigated the opto-electronic and magnetic properties of Mn(II)-doped ZnTe thin films by employing Density Functional Theory (DFT). In the absence of additional carriers, spin-up Mn-ta levels are fully occupied, leading to a super-exchange mechanism. The effect of additional p-type doping on the ferromagnetism is studied by considering the addition of hole carriers, Zn vacancies, and C co-doping, and we found that in all cases, coupling of hole carriers with the spin-up Mn-states causes the stability of the ferromagnetism in the Mn(II)doped ZnTe thin films. We discovered through the optical study that Mn(II) doping at the Zn site widens ZnTe's bandgap and produces spin-forbidden d-d transition peaks on the low energy side of the bandgap. The ptype defects in Mn(II)-doped films produce absorption peaks in the infrared region and improve the absorption efficiency. In addition, the optical bandgap and spin-forbidden d-d transition of Mn(II) to different modes of spinspin interactions were correlated, and we found a red shift of d-d intra-band transition peaks as well as an optical bandgap in the FM-coupled Mn(II) ions system and a blue shift in the AFM coupled ions system, supporting the experimental observations.