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题名	宽禁带半导体材料的光电特性研究
作者	王丹丹
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院大学
导师	刘雷
关键词	宽禁带半导体 氧化锌 石墨 碳化硅 硒化锌 晶格动力学
其他题名	Theoretical study of the new wide band gapsemiconductor photoelectric materials
学位专业	凝聚态物理
中文摘要	近些年来， 以GaN、ZnO、SiC、ZnSe以及金刚石等为代表的宽禁带半导体材料成为继以单质Si和GaAs为代表的第一代、第二代半导体材料之后迅速发展起来的第三代新型半导体材料。ZnO作为带隙宽度高达3.37eV、激子束缚能高达60 meV的宽禁带半导体，紫外激子发光有望在室温甚至更高温度下实现。然而，由于缺乏高效发光的pn结，高效的ZnO电泵激光迟迟没有实现。这是由于ZnO虽然容易实现n-型掺杂但是其p-型掺杂较难，多年来，重复获得高质量的p型氧化锌依然是有效获得ZnO基光电器件必须要解决的一个技术难题；另外，如何改善ZnO基光电器件的发光效率也一直被广泛关注。本文针对这两个问题进行了研究，取得的结果如下： （1）提出了氮掺杂氧化锌的优化p型新策略，这一策略能够有效抑制施主的补偿作用。我们通过分析氮在氧化锌表面的反应路径，证明了复合缺陷NZn-VO和NO-VZn是获得氮掺杂氧化p型导电性的关键因素。在锌极性面的生长过程中的亚稳态双施主复合缺陷NZn-VO不会引起同为施主的本征缺陷的补偿作用，起到抑制施主补偿的作用。而亚稳态双施主复合缺陷NZn-VO之后经触发可以越过势垒激活为稳定的双受主复合缺陷NO-VZn。混合泛函计算结果证明复合缺陷NO-VZn的最浅的受主能级位置位于价带顶之上0.23 eV处，相应的缺陷转变能级是0.16 eV，这一理论结果为实验上获得稳定可靠地p型氧化锌提供了新的可能的路径。 （2）我们的研究小组除了致力于通过N掺杂制备出高效的p型ZnO，还一直在探索增强ZnO发光效率的新思路，其中包括通过石墨烯表面等离子体来增强ZnO发光的策略。截止到目前为止，通过石墨烯提高ZnO基器件的发光效率已经在实验室取得一些令人振奋的结果，如将单层石墨烯薄膜直接放在ZnO薄膜上可以明显观察到ZnO的光致发光强度较没有石墨烯的情况下增强了3.2倍。我们的小组也做了一些相应的理论研究并取得了较好的结果。我们注意到，在石墨烯增强氧化锌材料的发光应用中，除了要制备出高质量的ZnO，如何制备出高质量的、平整的单层石墨烯的制备也至关重要。在石墨烯的众多生长方法中，其直接在宽禁带半导体SiC衬底上的外延生长引起了我们的注意。SiC作为一种宽禁带材料，除了其因饱和漂移速度、热导率特别适合制作高压、高温、大功率电子器件以外，较高的临界击穿电场以及较低的漏电流也保证了它是一种好的介质材料，可以作为电子器件的衬底。石墨烯可以直接在SiC表面外延生长，并且不需要将石墨烯重新转移到别的衬底上。因此如何在SiC表面获得高质量的石墨烯一直被广泛研究，其中如何降低石墨烯在SiC表面外延生长的生长温度是一个啓待解决的问题。本文针对这个问题进行了研究，取得的结果如下：对于在SiC（0001）表面石墨烯的外延生长，我们第一次提出空位辅助的Si-C键反转模型（Si-C flip model）。我们证明在石墨烯的生长过程中有几个关键阶段，也就是表面Si空位的形成、Si-C flip过程、表面Si原子蒸发过程、C原子积聚过程、表面分层以及石墨烯层的旋转过程等，在这几个关键阶段所需要的能量是不同的，我们提出可以通过在不同阶段控制能量束的方法来降低整个生长过程中的生长温度，并且通过严格控制能量束的空间分布和持续时间，我们有望在SiC沉底上得到高质量的并且尺寸和模式可控的石墨烯。 （3）作为另外一种Ⅱ-Ⅵ族宽禁带半导体材料，ZnSe具有与ZnO类似的结构特性，既有纤锌矿结构又有闪锌矿结构，且对其掺杂研究最多的也是N掺杂。在室温下ZnSe以闪锌矿结构稳定存在，但是从晶体学观点出发，闪锌矿结构具有高对称性，因此此滑移面较多，容易产生滑移位错，从而使得ZnSe基发光器件的发光寿命受到限制。而纤锌矿结构对称性较低，只有一个滑移面，因此纤锌矿结构的ZnSe外延层的滑移位错扩散会被抑制，这样可以有效提高发光器件的发光寿命。因此如何获得稳定的WZ结构的ZnSe一直被广泛研究，根据这个问题，我们研究了ZnSe的晶格动力学，获得的结果如下：通过密度泛函微扰理论进行晶格动力学研究发现，我们发现G点的声子振动模式可以作为区分闪锌矿结构ZnSe（zb-ZnSe）和纤锌矿结构ZnSe (wz-ZnSe)的关键证明。声子频率对zb-ZnSe的晶格应变有线性依赖关系，然而，在wz-ZnSe中，声子频率随应变的变化更加复杂。我们还发现氮原子的引入可以导致zb-ZnSe向wz-ZnSe转变。在zb-ZnSe和wz-ZnSe结构中引入N可以在500 cm-1以上引入三个频率较高的晶格振动模式，并且这三个振动模式在wz结构中的劈裂比在zb结构中更大。
英文摘要	In recent years, wide band gap semiconductor materials such as GaN, ZnO, SiC, ZnSe, diamond and other representatives developed rapidly in the third generation of new semiconductor materials after elemental Si and GaAs as the representative of the first generation, second-generation semiconductor material. As a well-known II-VI semiconductor, ZnO posses a direct band gap of 3.37 eV at room temperature and has a large exciton binding energy of 60 meV. So it’s expected to achieve UV exciton luminescence at room temperature. However, due to the lack of efficient luminescence p-n junction, efficient ZnO electric pump laser have been very slow to realize. This is caused by the fact that it is easy to realize n-type doping but hard to realize p-type doping for ZnO. Over the years, high quality p-type ZnO has been a technical problem in the optoelec-tronic application of ZnO. Moreover, how to improve the luminous efficiency of ZnO bansed photoelectric device has been a popular concern. Two chapters in the main text are mainly dedicated to these two problems, and the following results are obttained: (1) We put forward a new strategy of N doped p-type ZnO, which can suppress the spontaneous compensation from the intrinsic donors. By analyzing the reaction path of nitrogen at the ZnO surface, we proved that the complex defects NZn-VO and NO-VZn are essential for obtaining p-type conductivity in N doped ZnO. The hybrid functional calculation containing a mix of the exact exchange (36%) and the PBE functional proved that the most shallow acceptor level position of NO-VZn locates 0.23 eV above the valence band maximum and the defect transition level ε(0/-1) is 0.16 eV. This theoretical result provides a new possible path to obtained stable and reliable p-type ZnO experimentally. (2) What’s more, our team has been exploring new ideas which can enhance ZnO luminous efficiency including the strategy of graphene-plasmon-enhanced ultraviolet photoluminescence of ZnO. So far, some encouraging results have been obtained in improving the luminous efficiency of ZnO based devices through graphene. However how does the graphene work is unclear, it’s nessceary to further study the enhancing mechanism. In addition, access of high-quality graphene is an important factor in improving the luminous efficiency of ZnO based devices. As a wide-bandgap material, SiC is particularly suitable for the production of high pressure, high temperature, high-power electronic devices due to its saturation drift velocity, the thermal conductivity. Moreover, it can be used as a good substrate because of its higher critical breakdown field, and low leakage current. For example, graphen can be directly grown on SiC substrate and there’s no need to transfer the as-grown graphene to other sbustrate. Therefore, the epitaxial growth of high-quality graphene on SiC substrates has been studied extensively. In this research, how to reduce the growth temperature of graphene on SiC is an open problem to be solves. One chapter in the main text is mainly dedicated to the problems, and the following results are obttained: for the epitaxial growth of graphene on SiC (0001) surface, we propose a surface vacancy assisted Si-C flip mechanism for the first time.We demonstrate that there are several critical stages during the growth of graphene: the formation of surface Si vacancy、Si-C flipping、sublimation process of surface Si atoms、accumulation process of C atoms、eventually delamination and rotation of monolayer graphene. The energy intervals at various growth stages of graphene on SiC are actually different. Based on the identified energy intervals, we propose an optimized energetic-beam enhanced growth method for fabricating graphene with the desired size and patterns at a much lower temperature. (3)As another well-known II-VI semiconductor, ZnSe has similar structure properties with that of ZnO. They have two common structure polytypes, namely zinc-blend and wurtzite. And the most of the studies on doping of ZnSe is also N doping. Under normal conditions the as-grown bulk ZnSe exists in the zinc-blend (ZB) phase. However, from a crystallography point of view, the high-symmetry ZB structure contains many glide planes and glide dislocations which limit the lifetime of ZnSe-based light-emitting devices. While the low-symmetry WZ structure contains only one primary glide plane and the diffusion of glide dislocations in the epitaxial ZnSe layer is suppressed, so the luminescence lifetime of the light emitting devices can be effectively improved. Therefore how to obtain a stable ZnSe WZ structure has been extensively studied. According to this problem, we have studied the lattice dynamics of ZnSe, and the results obtained are as follows. Based on the density-function perturbation theory, we found the phonon vibration modes at Γ can be characteristic to distinguish between ZB-ZnSe and WZ-ZnSe. For ZB-ZnSe, the optical phonon frequency at Γ is linearly dependent on the lattice strain, while the dependence is more complex for WZ-ZnSe. We also found that the introduction of a nitrogen atom to ZnSe lattice may result in three new lattice vibration modes with the frequencies above 500 cm-1, and the splitting of the three new vibration modes in WZ structure is greater than in ZB structure.
公开日期	2015-12-24
内容类型	学位论文
源URL	[http://ir.ciomp.ac.cn/handle/181722/48903]
专题	长春光学精密机械与物理研究所_中科院长春光机所知识产出
推荐引用方式 GB/T 7714	王丹丹. 宽禁带半导体材料的光电特性研究[D]. 中国科学院大学. 2015.

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