【作者】 欧阳桂仓；

【导师】 叶志清；

【作者基本信息】 江西师范大学 ， 光学， 2008， 硕士

【摘要】 氧化锌(ZnO)是一种新型的Ⅱ-Ⅵ族多功能直接带隙化合物半导体材料,在室温下禁带宽度为3.37eV,束缚激子能高达60meV。在晶格特性和能带结构方面与GaN有许多相似之处,拥有可以比拟的光电特性,而且还具有更高的激子束缚能以及较低的生长温度,被认为是有望取代GaN的新一代短波长光电子材料,因而成为半导体材料科研领域的一个热门课题。但是,从1996年首次报导ZnO薄膜的室温紫外发射距今已有十余年,ZnO基激光二极管、发光二极管等短波长光电器件仍未达到实用化的水平,其中一个主要原因是高质量的p型ZnO薄膜的稳定、可重复制备工艺尚未实现。围绕这种背景,本论文基于密度泛函理论,以第一性原理为研究方法,对本征ZnO及掺杂ZnO进行模拟研究,从以下四个方面开展了工作:首先,研究了本征ZnO的电子结构,通过对能带结构、总体态密度、分波态密度的分析,说明了ZnO为直接宽带隙半导体,呈现出n型导电性,计算结果同时表明锌填隙( Zn_i)是造成p型掺杂困难的主要原因。其次,我们还详细地计算了本征ZnO的复介电函数、复折射率、反射光谱、吸收光谱、能量损失函数等光学性质,探讨了微观结构与宏观光学响应的关系。通过比较,我们的计算结果和其他理论、实验值符合的很好。然后,研究分析了以Ⅲ族(B、Al、Ga、In)原子对ZnO进行n型掺杂,在导带底出现掺杂原子贡献的大量电子,引起ZnO体系电导率的提高。随着Al掺杂浓度的增大,ZnO的整个能带向低能方向漂移,费米能级进入导带,简并化加剧。由掺杂模型的几何结构优化之后所得的晶格常数与实验值非常=接近,说明我们的计算结果是可信的。最后,以不同N掺杂浓度和N+Al共掺的方式分别进行p型掺杂,计算结果表明:N单元掺杂时由于ZnO的自补偿作用,受主N在ZnO中的溶解度较低,难以实现p型掺杂;而N+Al共掺能有效提高受主N的溶解度,提高了ZnO体系空穴浓度,在价带顶附近形成了浅受主能级,有利于p型ZnO的形成,为实验上制备p型ZnO薄膜提供理论依据。更多还原

【Abstract】 Zinc oxide (ZnO) is a new multifunctional compound semiconductor of II-VI group, with a wide direct band-gap of 3.37eV and a high exciton binding energy of 60meV at room temperature. Compared with GaN, it has many similarities in the crystal lattice characteristics and the band structure, and has photo-electric properties which may compare, moreover, it also has a higher exciton binding energy as well as the low growth temperature, therefore, it was considered to be a new kind of photo-electric material in shortwave length as GaN, and becomes a popular topic of semiconducting material scientific research domain. However, from 1996, stimulated UV emission of Zn0 thin film at room temperatwe was reported for the first time, it has passed more than ten years by now, but the short wave length photoelectric such as the ZnO base light emitting diode and the light emitter diode apparatus had still not achieved the practical level. One of the most important reasons is that the reliable and reproducible technique to grow high quality p-type ZnO is not found yet.Regarding these reasearch background, and based on the density functional theory (DFT), we take the first principles as research technique to investigate natural ZnO and doped ZnO, specifically include the following four aspects:Firstly, we study the geometric structure of the natural ZnO, through the analysis of the band structure, the total density of states and partial density of states, we know that ZnO is a direct wide band-gap semiconductor, which presents n-type conductivity, the computed results also indicate that the zinc calking is the main difficulty in p-doping.Secondly, to explore the relationship between the micro-structure and the macroscopical optical response, we calculate the dielectric function, refractive index, reflectance spectra, absorption spectra, the energy loss function and other optical properties in detail. By comparison, the resultse obtained by our calculations are in good agreement with other theoretical results and experimental data.Then, by analysing the properties of the n-type ZnO doped byⅢgroup atoms (B,Al,Ga,In), We found that there are a lot of carrier in the bottom of the conduction band, which causes the improvement for conductivity of the ZnO system. When doped with different concentration of Al, following the increase of the concentrations, the whole band drift to the lower-energy, and the Fermi level move into the conduction band, appear greatly limited. Our crystal constants, obtained from the doped geometry structure, are close to the experimental datas, which shows that our computed result is credible.Lastly, we have researched on p-type doping and p-type codoping for ZnO, by doped with different concentrations of N and codoped with N and Al, respectively. Our calculations shows that N-doped is difficult to achieve p-type doping for ZnO because of the self-compensation, while codoped with N and Al can effectively improve the solubility of the acceptor N and the hole concentration of ZnO system, then form a shallow acceptor level near the top of valence band, which is very helpful for p-type doping for ZnO. Of course, it provide the theory basis for making ZnO thin film in experimental methods.更多还原