| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Thursday Sessions |
| Session 2D+EM+MI+NS+QS+SS-ThM |
| Session: | Dopants, Defects, and Interfaces in 2D Materials |
| Presenter: | Thilini K. Ekanayaka, University of Nebraska-Lincoln |
| Authors: | T.K. Ekanayaka, University of Nebraska-Lincoln G. Gurung, University of Nebraska-Lincoln G. Rimal, Rutgers University S. Horoz, Siirt University, Turkey J. Tang, University of Wyoming T. Chien, University of Wyoming T. Paudel, University of Nebraska-Lincoln A.J. Yost, University of Nebraska-Lincoln |
| Correspondent: | Click to Email |
Semiconducting quantum dots (QDs) are desirable for solar cells due to the ability to tune the band gap by changing the QD size without changing the underlying material or synthesis technique. Doping QDs with a transition metal is one way of further tailoring the electronic band structure and magnetic properties of QDs in order to improve overall device performance. Understanding the mechanisms causing the change in the electronic band structure and magnetic properties due to transition metal doping is important to device-by-design schemes. In this study, we measure the effects of Mn dopants on the surface electronic band structure of ZnS and CdS QDs using scanning tunneling microscopy/spectroscopy and photoemission spectroscopy. In both the ZnS and CdS systems, a decrease in band gap upon introduction of Mn is observed. Additionally, a rigid band shift was observed in ZnS upon Mn doping It is argued, using X-ray photoemission spectroscopy, that the rigid band shift is due to a hole-doping mechanism caused by the formation of Zn vacancies accompanied by a Mn3+oxidation state which leads to the reduction in total S vacancies as compared to the undoped ZnS system. No band shift was observed in CdS upon Mn doping, but a strong sp-d hybridization takes place which results in a significant band gap reduction. Furthermore, induced midgap states originating from the Mn dopant appear in the surface electronic band structure of Mn: CdS. Measurements of the magnetization of Mn doped and undoped ZnS and CdS confirms the presence of d0 ferromagnetism. The magnetization is reduced and the coercive field is increased post Mn doping which suggests the anti-ferromagnetic alignment of Mn dopant atoms. Density Functional Theory calculations support the Mn anti-ferromagnetic alignment hypothesis and a ground state with Mn in the 3+ valence. This study provides important information on the role of dopants and vacancies in dilute magnetic semiconductor quantum dot materials for applications in photovoltaics and spintronics.