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Investigation of the Properties of Manganese Doped Lead Sulfide
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Dissertation
Investigation of the Properties of Manganese Doped Lead Sulfide
2017
Overview
The study of diluted magnetic semiconductors (DMS) has been a trend for many decades. Although many DMS materials have been identified, the application to semiconductor technology has remained stagnant. An important aspect of research in this field is the search and application of such materials. For this dissertation, a DMS material - manganese doped lead sulfide (MnPbS) is identified and studied. Specifically, the material has been investigated for the electronic, optical and magnetic properties. This material is found to be useful for studying interesting fundamental physics as well as for possible technological applications. The material has been studied in various ways. First, quantum dots are prepared using pulsed laser deposition and show an increase of the bandgap as well as decrease of absorbance in the visible/NIR range as a result of Mn doping. The quantum dots are also applied as solar energy absorber to construct a quantum dot sensitized solar cell. When used together with a wide bandgap photoanode (Zn2SnO4 nanowire), the system is more efficient in converting photons to electrons and generating higher photocurrent compared to undoped PbS. The results show the promise of MnPbS for the construction of more efficient solar cells. In another study, the magnetotransport properties of MnPbS are compared to PbS. It is found that the films are highly disordered and insulating, and show variable range hopping (VRH) at low temperatures. At very low temperatures, a soft Coulomb gap is found to arise in MnPbS that changes to a hard gap at lower temperatures. The hard gap can be closed by magnetic field and reverts to the soft gap. It is found that the influence of bound magnetic polarons (BMP) results in this behavior. The final study on MnPbS compares the effect of sulfur vacancy and possible effect of the Mn dopants on the magnetic properties. It is found that films with high concentration of sulfur vacancies are ferromagnetic at room temperature while lower concentration of sulfur vacancies result in nonmagnetic films. X-ray absorption spectroscopy reveals the nature of Mn dopants and shows that the Mn does not directly influence the ferromagnetism in the material. Both PbS and MnPbS are thus identified to be d0 ferromagnets.
Publisher
ProQuest Dissertations & Theses
Subject
ISBN
0438533844, 9780438533844
