Study Of Electronic Properties Of Diamond Semiconductor

As a wide band-gap semiconductor, diamond is of outstanding physical and chemical properties. It has been associated with a broad range of applications in advanced-technology fields, especially in those of high temperature, high frequency and high power electronic devices. However, the application of diamond as an electronic material is limited by the lack of the available n-type material and thus the high quality diamond device has not yet been achieved although its p-type material can be obtained. Consequently, it is a key issue to obtain an available n-type diamond material for the application of diamond semiconductor.Great efforts have been made both theoretically and experimentally to obtain available n-type diamond materials. In general, it is attempted to dope N or P dopant into diamond. However, it is difficult to realize the purpose owing to various reasons. For example, it has been considered that the substitutional P (P_s) is the most available donor in diamond. However, the electronic properties of P-doped diamond are not satisfied by the carrier compensation effect. Experimental study indicated that the compensator density increases monotonically with the P concentration increasing. To improve the doping efficiency, it is necessary to reveal the origin of the carrier compensation effect and reduce the carrier compensation ratio in P-doped diamond. So far, most of the interest for the n-type diamond materials has been limited to doping with the group I elements Li and Na; group V elements N, P, As and Sb; group VI elements O, S, Se and Te. Unfortunately, the available n-type diamond has not yet been achieved. So it is essential to look for other donor dopants. In addition, the experimental results showed that H atom plays many roles on the electronic properties of diamond, and there is still controversial about the origin of H effect on the electronic properties of B-doped p-type diamond. Therefore, it is important to carry out the related study for the application and exploitation of diamond materials. In this dissertation, we studied the related issues mentioned above based on density functional theory: 1. We explored the origin of carrier compensation in P-doped diamond. The results showed that the vacancy concentration increases with the P content increasing in diamond and the monovacancy, divacancy and trivacancy are formed sequentially. The compensation ability of vacancy complexes increased in the order monovacancy < divacancy < trivacancy. This work provides a theoretical foundation for the understanding of mechanism of carrier compensation and the improvement of electronic properties in P-doped diamond.2. We studied the effect of Be, Mg and halogen on the electronic properties of diamond. It was found that the interstitial Be- or Mg- doped diamond are of n-type metal conductivity character. And substitutional I-doped diamond also showed a good n-type behavior. The further results indicated that H atom could reduce donor behavior in diamond and the donor dopants doping diamond should be carried out in H-poor conditions. The work gives a theoretical foundation for looking for possible donor of diamond and doping conditions.3. We have systemically investigated the influence of H atoms on the electronic properties of passivated system. According to the comprehensive understanding for the interaction between H atoms and passivated system, it was found that H atoms made the passivated system show n-type, p-type or insulator behavior dependence on the hybridization between B_s and H orbitals. The results provide a theoretical foundation for controlling the electronic properties of doped diamond reasonably in experiment.The structure of the dissertation is as follows.Chapter 1 is INTRODUCTION, in which we introduce the background and significance of dissertation and elucidate the theoretical and actual significance of the dissertation. It is composed of fundamental properties of diamond, physical and chemical properties of diamond, research progress of diamond and research contents.Chapter 2 is FOUNDATION OF DENSITY FUNCTIONAL THEORY, in which we briefly introduce the basic concept of DFT and review its recent progress. It is composed of first-principle calculation and density functional theory, exchange-correlation energy functional, plane-wave and pseudopotential method, improvement and extension of DFT. Chapter 3 is THEORETICAL CHARACTERIZATION OF CARRIER COMPENSATION IN P-DOPED DIAMOND, in which we explore the origin of carrier compensation in P-doped diamond based on DFT. It is composed of background, calculations and method, results and discussion and conclusions.Chapter 4 is EFFECT OF BE,MG AND HALOGEN DOPANTS ON ELECTRONIC PROPERTIES OF DIAMOND, in which we study the effect of Be, Mg and halogen on the electronic properties of diamond. It is composed of background, calculations and method, effect of Be,Mg and H complexes on electronic properties, effect of Halogen X (=F, Cl, Br, I) on electronic properties and conclusions.Chapter 5 is EFFECT OF HYDROGEN ON ELECTRONIC PROPERTIES OF B-DOPED DIAMOND, in which we have systemically investigated the influence of H atoms on the electronic properties of passivated system. It is composed of background, calculations and method, results and discussion, effect of H on conductivity of B-doped diamond by experiment and conclusions.Chapter 6 is SUMMARY AND PROSPECT, in which we summarize the conclusions of this dissertation and previewed the further studies.