Study Of N-type Doped Diamond By First-principles

The covalent bonds between carbon atoms in diamond are extremely strong, which gives diamond attractive physical and electrical properties, such as high carrier mobility, extremely high electric breakdown field and high thermal conductivity. Therefore, diamond has been recognized as a promising material for electronic devices. The p-type material can be easily achieved by boron (B) doping, but the lack of effective n-type conductivity has hindered the use of diamond-based devices in electronic applications. Effective n-type doping remains unavailable. It has proved to be a significant challenge for effective n-type doping of diamond. In recent years, the researchers have focused on phosphorus, nitrogen and sulfur doping primarily. Nitrogen (N) may exist in natural diamond, or be incorporated into diamond by chemical vapor deposition and high temperature high pressure method. Substitutional Nitrogen is a well-known n-type dopant candidate. However, the N-doped diamond is not expected to yield useful conductivity at room temperature due to a very deep donor level (1.7eV) below the bottom of the conduction band. Phosphorous has been reported to be a more shallow impurity (0.6eV) and Koizumi has succeeded in growing high quality P-doped diamond, however, the n-type diamond obtained by P-doping has low electron mobility, which makes its problematic application at room temperature. Sulfur(S) doping was reported to appear n-type conductivity, which may be good donor material. In addition, Li, Na, As, Sb and other impurities which can show donor characteristics in diamond have also been reported, and Na is limited to theoretical study.Despite the recent efforts in the study of n-type diamond, high-quality electronic devices based on n-type conducting diamond have not been obtained up to now. Previous studies have demonstrated that single donor dopant mentioned above can't provide available n-type conducting diamond, thus it is necessary to look for other ways to obtain applicable n-type conductivity. The codoping effects have shown many advantages in tuning the electronic structures of semiconductors and may overcome or avoid some disadvantages of the single doping, which may be a useful way to find donor complexes. In addition to the diamond bulk, the diamond surface is another interesting subject, which has many significant properties, such as the negative electron affinity, the p-type surface conductivity. Hydrogen termination of the surface has been expected to play a key role in the realization of diamond's surface conductivity. In the present work, First principles DFT were carried out to study the codoping effects of boron and chalcogen on conductivity properties of diamond and the doping effect of N/P on electronic properties of diamond (100) and (111) surfaces.Chapter 1, we introduce the fundamental relevant properties of diamond: physical and chemical properties of diamond, structure of diamond, the classification of diamond, semiconductor devices made of diamond and their applications, preparation of diamond films, and the research progress of n-type diamond.Chapter 2, we introduce the basic concepts of density functional theory, exchange-correlation functional and pseudopotential plane wave method. We give a brief description of the calculation software used in this article.Chapter 3, to explore the codoping effects of B and chalcogen X (X=O, S, Se and Te) atoms on the electronic properties and conductive properties in the doped diamond. Based on DFT calculations, we calculated and analyzed the band structure, total density of states (TDOS), projected density of states (PDOS), and formation energies of B and X (X=O, S, Se and Te) codoped diamond.Chapter 4, this Chapter mainly focuses on atomic and electronic structures of the diamond (100) and (111) surface with substitutional N and P atoms. Total density of states (TDOS), projected density of states (PDOS), and band-structure calculations have been performed, and it predicts the feasibility of achieving the n-type diamond theoretically by studying the effects of different doping sites on electronic structure in diamond.Chapter 5, we summarize the dissertation and preview the further studies.