Study Of Energy Band Structure Of Strained ZnO

Zn O based(strained) quantum well,(strained) superlattice(SL) and Strain-compensated Multi-quantum Wells(SCMQW) and such strained heterostructure are valuable in laser,light detector, long wavelength optical communication system, high-speed electronic devices and silicon-based optoelectronic monolithic, which has become a focus of research. Theoretical studies on electrical and optical properties related to band structure of strained Zn O are rarely reported,investigations on the band structure of strained Zn O material are of important value on both theoretical research and engineering application.The band structure of Zn O will change with the stress field, which influences on the electrical and optical properties of the material. Both biaxial strained Zn O band structure model and doping strained Zn O model are established in this paper to systematically and comprehensively describe the relationship between energy band,electron effective masses, holes effective masses and degree of strain, and furtherly understand the physical properties of strained Zn O materials, as well as choose the stress method and strength in Zn O strained devices(superlattice, quantum well in especial) design to provide the theoretical basis. The main contents and results of this paper can be summarized as the following three parts:1. Based on the kp theory of Luttinger-Kohn and Bir-Pikus, strained Zn O grown on relaxed Znl-x Mgx O substrate by epitaxial growth is studied, the E-k analytical expressions and hole effective masses expressions along different crystal orientation for the valence band of strained Zn O are obtained. Apparent movement of valence band edges at Γ point are revealed, the two-dimensional equal-energy lines of “light hole band”, “heavy hole band” and crystal splitting band of unstrained Zn O and strained Zn O/Zn0.7Mg0.3O are obtained, and the change rules of electron and hole effective masses under stress are also investigated. The research results reveal that there is almost no change in effective masses of “light hole band” and “heavy hole band” along [00k]and [k00] orientation under strain and the strain leads to obvious decrease in effective masses of crystal splitting band along [00k] and [k00] orientation. The analytical results of E-k analytical expressions and quantitative data of related important physical parameters can provide a theoretical foundation for understanding applications of strained Zn O.2. Based on the theories of strain tensor, physical model of strained Zn O is set up using first-principles calculations of plane wave Norm-Conserving pseudo-potential technology based on Density Functional Theory. Firstly,the modules of unstrained and strained Zn O are set up, in which the magnitude of stress is characterized by Mg content of Znl-x Mgx O substrate, the conduction and valence band structures of strained Zn O are obtained by using first-principles calculations based on DFT, then the quantitative models of effective mass are also obtained. At the same time, the analysis method of band structure and optical properties of strained Zn O/Znl-x Mgx O is investigated using CASTEP, and the relationshiop between band structure, effective mass, optical reflectivity, refractive and the extent of strain are obtained. The research results are compared with the results of kp methods, which provides another effective means of analysing of electron and hole effective mass in strained Zn O. Based on the model of stained Zn O/Znl-x Mgx O, the models of Nb-doped Zn O/Znl-x Mgx O are set up,and the influence of substrate on the band and effective mass on doped Zn O are also studied. CASTEP is employed for its reliability and simplicity in this paper, and it provids an effective way to analyze the band structure of strained Zn O and many physical parameters. This study also gives a valuable solution to stress models of similar materials.3. Doping is the main form in which the stress is introduced, the models of Al mono-doping of Al-Sn co-doping strained Zn O systems are set up in order to investigate the doping stress effect by using first-principles calculations based on DFT. The electrical properties including crystal structure, band structure, effective mass and so on are analyzed, and optical properties such as dielectric function, absorption spectrum,reflectance spectrum have been calculated and discussed in combination with the experimental results reported in literatures. The research results reveal that the impurity binding energy Ef decreases in turn of pure Zn O Al mono-doping of Al-Sn co-doping Zn O systems, which indicates that Al-Sn codoping is easier than Al mono-doping; Al mono-doping and Al-Sn codoping which have smaller electron and hole effective masses than pure Zn O are better doping chooses, and theirs electrons have better transportation behaviors and lower ionization energy; in addition, for Al-Sn co-doping Zn O, one new ultraviolet peak located at 300 nm in absorption spectra, the UV absorption value increases, and the reflectivity and absorptivity of Al-Sn co-doping Zn O are larger than pure Zn O, indicating that the average optical transmittance in visible range significantly reduced. The analytical models and research results can expand the application scope of research results of this paper, provides a basis for the application of electrical and optical characteristic of strained Zn O material and design and optimization of device performance.