First-principles Study Of The Defect Properties Of3D Transition Metal Based Ⅱ-Ⅵ Semiconductor Materials

The rapid development of modern information industry is intensively related to thecontinuous innovation of semiconductor materials. According to the locations of theircomponents in the periodic table, semiconductors can be categorized into IV, Ⅱ-Ⅵ, III-V, IV-VI, and II-IV-VI etc. Among them, the Ⅱ-Ⅵ semiconductor received people’s attention at thevery beginning due to their unique properties of direct band gaps, wide range of light emittingfrequencies, easy practice of isovalent doping and so on. Traditional semiconductors containthe binary or ternary compounds consisted of the group II (Zn, Cd, and Hg) and group VI (S,Se, Te, and O) elements. Compared with the tradition systems, the3d transition metal (3d TM)based Ⅱ-Ⅵ semiconductors may couple with magnetic characteristics, and thus show newproperties, e.g. the unique spin transport and the magneto-optic coupling.During the preparation, various dopants are often deliberately introduced into thesemiconductor systemswith the purpose oftuning their optical and transport characters.Meanwhile, in general, it is hard to exclude all of the crystal defects as the samples preparedunder the lab conditions. It has been the most fundamental issue for semiconductor functionaldesigns to make clear how to effectively utilize the formation and distribution of the potentialdopants and defects. Compared with other simulation methods, the first-principles calculations,on one hand, do not depend on any empirical parameter, and are able to simulate and explainthe properties ofvarious materials at the electronic level. On the other hand, they are capable ofpredicting structural and other properties in various kinds of materials, being the guide forexperimental approaches, and really attracted more and more attentions by scientificresearchers.Based on the first-principles calculations, we will study the structural and the couplingproperties of the doped systems of ZnTe:TM, CdTe:TM and MnTe:TM. We have alsoinvestigated the defect formations and their influences on the carrier characters of wurtzite (wz)CoO and MoO.The arrangements of this dissertation are as follows:In Chapter One, a systematic introduction will be given on the research background of the traditional Ⅱ-Ⅵ and3d-TM based Ⅱ-Ⅵ semiconductors. In Chapter Two, we will specificallyintroduce the theoretical foundations of the density functional theory (DFT).Chapter Three mainly introduce the researches of the structural and the coupling propertiesof the doped systems of ZnTe:TM, CdTe:TM and MnTe:TM.We find that the Mnantiferromagnetic (AFM) background significantly decreases the clustering trend of doped TMimpurities except Ni, and also effectively enhances the magnetic couplings between Fe, Co andNi impurities. Both the degrading of clustering trend and the enhancement of magnetic couplingare expectedfor MnTe doped with Fe, indicating that the host AFM background may bebeneficial to semiconductor materials ofhigh Currie Temperature (TC).Chapter Four mainly introduce the research results of intrinsic defects-related properties ofwurtzite CoO and MnO. For wurtzite MnO system, we find that the p/n conductivity could betuned through adjusting the oxygen partial pressure of the growth condition. O-rich conditioncorresponds to p-type conductivity with the mainly formed defects of Oi, Oi+OMn, OMnand VMn,while O-poor condition corresponds to n-type conducting with the dominate defects of VO, MnO,Mniand VO+Mni. For wurtzite CoO system, it is very easy to be designed as p-typesemiconductor, but hardfor the n-type one.We expect that the tunable p/n conductivity ofwurtzite MnO could brings more application prospects for wurtzite semiconductors.Chapter Five will concisely introduce my on-going and planned researches.The summary of this dissertation is arranged at the end, with the related references and theachievements during the Ph.D candidate period.