| Summary: | 碩士 === 國立彰化師範大學 === 物理系 === 90 === Although the Ⅲ-nitride semiconductor materials have been applied extensively to various optical and electronic devices, there still exist a lot of physics related to the Ⅲ-nitrides that need to be clarified. In my thesis, I focus on the investigation of the band structures of the Ⅲ-nitrides. The simulation program that I use in this thesis is CASTEP, which is provided by the National Center for High-Performance Computing, National Science Council of the Republic of China. For the simulation of each semiconductor material, the band straucture is obtained after the atomic structure, lattice contants, and composing elements are properly defined. After then, more properties of the semiconductor materials under study, such as the band-gap energy, the valance band width, and the direct/indirect band-gap characteristics, may be analyzed from the band structures.
In the first and second chapters, I do a brief overview on some essential properties about crystal structures and composing elements to help the readers understand the Ⅲ-nitrides. Moreover, I give a brief introduction about the developmental hsitory of band structure calculation and the CASTEP simulation program that I use for this research.
The main contents of my thesis start from chapter 3. In this chapter I do a series of simulations for common AlGaInN of wurtzite structure to obtain the band-gap energies, the valence band widths in different compositions, and the bowing parameters of the ternary Ⅲ-nitrides. For actual crystal growth, the Ⅲ-nitride thin film might suffer from compressive or tensile strain due to the lattice mismatch between the active layers and the substrate or other layers in the neighborhood, which results in the deformation of the crystal lattice. Hence, I also investigate the variation of the band-gap energies, valence band widths and bowing parameters under different degree of strain. In addition, there exist an indium-rich phenomenon when the compositon of the indium in ternary InGaN is high. A few simulations regarding this issue have also been conducted.
The contents discussed in chapter 4 are similar to that in chapter 3, except that the cystal structure is changed from wurtzite to zinc-blende. For each ternary zinc-blende Ⅲ-nitride semiconductor, it can be either a direct band-gap material or an indirect band-gap material, depending on the composition of the composing elements. Hence, special attention is paid to the transition from a direct band-gap semiconductor to an indirect band-gap semiconductor for each ternary Ⅲ-nitride semiconductor material under study.
Based on the results obtained in chapters 3 and 4, I try to simulate another new material system in chapter 5 - the ternary B(Al,Ga,In)N. Since this ternary B(Al,Ga,In)N semiconductor is less investigated in the past few years, much effort is still required to explore its characteristics. Simulation results indicate that the ternary B(Al,Ga,In)N semiconductor materials have relatively high bowing parameters. The possible cause for this phenomenon will be discussed. Finally, in chapter 6 I will review the major results in my thesis and make a conclusion.
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