高质量ZnO薄膜的MOCVD外延生长与原位掺杂

发布时间：2018-07-25 19:26

【摘要】：ZnO材料的激子束缚能为60meV,是一种具有优越的光电性质的宽带隙半导体材料,在紫外探测器件和激光器等短波长光电器件方面具有重要的应用前景,然而ZnO的p型掺杂难题仍然是其实际应用的最大障碍。氮元素是目前公认的最有可能成功实现稳定、高效的ZnO的p型掺杂的元素,因此我们希望通过研究ZnO中N的掺杂机制和缺陷行为,并研究退火过程对材料微观结构和光电特性的影响,为实现p型ZnO导电这一前沿难题提供科学可行的思路和方法。ZnO材料是一种极性氧化物半导体。由于O面和Zn面极性的ZnO材料在物理和化学特性方面存在较大差异,包括掺杂效率、表面形貌、电学输运、表面吸附、表面重构与缺陷、发光特性和肖特基接触等,因此极性控制对材料质量和最终光电器件的性能都具有非常重要的影响。通过不同的预处理方法实现对ZnO的极性控制是获得高质量ZnO材料的关键前提,因此我们研究了不同预处理对ZnO极性、外延模式和杂质污染的影响,进而优化生长条件实现高质量ZnO的二维层状外延。另外,中间带太阳电池因具有结构简单、成本低且理论效率非常高等优点,具有很好的发展前景。基于Ⅲ-Ⅴ和Ⅱ-Ⅵ的高失配合金体系是目前中间带光伏材料研究的重点,理论和实验都已经证明了ZnTe:O和GaAs:N中间带的存在。制备高质量的ZnTe:O单晶薄膜也是本文的重点研究内容之一本文的主要成果如下：1、利用MOCVD方法在ZnO单晶衬底上同质外延制备出高质量的ZnO单晶薄膜,并研究了衬底极性和衬底预处理温度对外延生长模式、表面形貌、晶体质量、缺陷形成、杂质浓度和发光特性的影响。研究表明,Zn极性面ZnO衬底易诱导二维层状外延生长,表面具有原子级平整度,且有效抑制MOCVD低温生长造成的非故意碳掺杂污染问题,具有较好的紫外激子发光特性。过高的预处理温度会导致衬底表面缺陷处形成严重的解吸附,从而影响后续二维层状同质外延。研究发现1000℃预处理Zn极性面ZnO单晶衬底是实现高品质的ZnO同质外延最合适的条件。2、利用MOCVD方法在ZnO模板衬底通过原位掺杂制备出高质量ZnO:N薄膜,研究了材料中补偿施主的性质和行为,并使用快速热退火的方法成功激活了ZnO:N中可能的受主,通过C-V测量观察到p型导电特征。采用Hall测量、变温光致发光谱和拉曼散射等手段揭示了N掺杂及后续退火对材料缺陷结构的影响。研究发现,No-Zni复合体和Zni团簇是ZnO:N中主要的补偿施主,而NHx占据Zn位或者N2占据Zn位是可能的稳定浅受主,退火导致间隙锌缺陷团簇形成,并在高温下分解和脱附。3、利用MOCVD方法通过Te-N共掺ZnO样品并进行退火的方式研究了ZnO本征缺陷(Zni, VZn)的行为。Zni团簇在ZnO中是一种浅施主,并且在Te-N共掺ZnO以及快速退火样品中能够稳定存在。同时发现Te-N共掺在抑制本征缺陷Zni团簇中起到了明显的作用。可能的浅受主为No-Zn-Te, VZn-No复合体以及Vzn团簇,单独的Zni和VZn可能会相互结合,并在高温下扩散而离开晶格。然而,单独的Zni和VZn团簇在N元素的掺杂的环境中可能是稳定的。在N掺杂ZnO薄膜中,一个合适的设计来增加VZn团簇并同时抑制Zni和Zni团簇是一条可能的形成稳定的可靠的p型ZnO材料的途径。4、通过MOCVD的方法在c轴蓝宝石上外延利用低温非平衡条件制备出了ZnTe:O高失配合金单晶薄膜,并对材料进行了热退火研究,重点研究了原位氧掺杂和热退火对材料微观结构、化学价键状态和中间带发光特性的影响。研究发现,原位氧掺杂并未导致晶格发生严重畸变,甚至产生其他物质相,其单晶特性说明了MOCVD制备方法的技术优势。通过面对面覆盖的退火优化方式,有效避免了ZnTe:O表面被氧化和改善了材料的晶体结构质量,同时在～1.9eV处形成以氧等电子陷阱为主的中间能带,与能带非交叉模型计算的结果高度一致。优化MOCVD制备条件及退火处理方法有利于实现中间带由非辐射复合的局域态向辐射复合的扩展态过渡,为提高ZnTe:O基中间带太阳电池转换效率提供可能。
[Abstract]:The exciton binding energy of the ZnO material is 60meV, a wide band gap semiconductor with superior photoelectric properties. It has an important application prospect in the UV detector and the laser and other short wave long light electrical appliances. However, the P doping problem of ZnO is still the biggest obstacle in its practical application. The nitrogen element is the most widely recognized at present. It is successful to achieve stable and efficient P doped elements of ZnO, so we hope to study the doping mechanism and defect behavior of N in ZnO, and to study the effect of annealing process on the microstructure and photoelectric properties of the materials, and to provide a scientific and feasible way of thinking and method for realizing the leading problem of P ZnO conduction, the.ZnO material is a kind of polar oxide. Semiconductors. Because of the physical and chemical properties of the O and Zn surface polarity ZnO materials, such as doping efficiency, surface morphology, electrical transport, surface adsorption, surface reconstruction and defects, luminescence properties and Schottky contact, polarity control has a very important effect on the material quantity and the performance of the final photoelectric device. The polarity control of ZnO by different preconditioning methods is the key prerequisite for obtaining high quality ZnO materials. Therefore, we studied the effects of different pretreatments on ZnO polarity, epitaxial mode and impurity pollution, and then optimized the growth conditions to realize the two-dimensional layered epitaxy of high quality ZnO. In addition, the intermediate band solar cells have the structure. The advantages of simple, low cost and very high theoretical efficiency have good prospects. The high mismatched alloy system based on III - V and II - VI is the focus of the research on the intermediate band photovoltaic materials. Both theory and experiment have proved the existence of the ZnTe:O and GaAs:N intermediate bands. The preparation of high quality ZnTe:O single crystal films is also the focus of this paper. The main achievements of this paper are as follows: 1, high quality ZnO single crystal films were prepared on ZnO single crystal substrate by MOCVD method. The effects of substrate polarity and substrate preprocessing temperature on the growth mode, surface morphology, crystal quality, defect formation, impurity concentration and luminescence properties were investigated. The surface ZnO substrate is easy to induce two-dimensional layer epitaxy growth. The surface has atomic level flatness, and it effectively inhibits the unintentional carbon doping caused by the low temperature growth of MOCVD. It has better ultraviolet luminescence characteristics. The high pretreatment temperature will lead to the serious desorption of the surface defects on the substrate surface, thus affecting the subsequent two-dimensional layer. It is found that the pretreatment of Zn polar surface ZnO single crystal substrate at 1000 C is the most suitable condition for achieving high quality ZnO homogeneity epitaxy.2. MOCVD method is used to prepare high quality ZnO:N film on the ZnO template substrate by in-situ doping. The properties and behavior of compensating donor in the material are studied and the method of rapid thermal annealing is successful. The potential acceptor in ZnO:N is activated by C-V measurement and the P type conductivity is observed. The effect of N doping and subsequent annealing on the structure of material defects is revealed by means of Hall measurement, variable temperature photoluminescence spectrum and Raman scattering. The study shows that the No-Zni complex and Zni cluster are the main compensation donors in ZnO:N, and NHx occupies Zn bit or N2 in ZnO:N. According to the Zn position is a possible stable shallow recipient, annealing leads to the formation of the gap zinc defect clusters, and decomposes and departs.3 at high temperature. The ZnO intrinsic defect (Zni, VZn) is studied by the MOCVD method Co doped ZnO samples and annealed in the way of ZnO. The.Zni cluster is a shallow donor in ZnO, and in Te-N Co doped ZnO and fast annealing samples. There is a stable presence in the product. It is found that Te-N co doping in the inhibition of the intrinsic defect Zni clusters has played an obvious role. Possible shallow recipients are No-Zn-Te, VZn-No complex and Vzn clusters, and separate Zni and VZn may be combined and diffuse at high temperatures and leave the lattice. However, the individual Zni and VZn clusters are doped in N elements. It may be stable in the environment. In the N doped ZnO thin film, a suitable design to increase the VZn cluster and inhibit Zni and Zni clusters is a possible way to form a stable and reliable P type ZnO material,.4. By the MOCVD method, ZnTe:O high mismatch alloy single crystal is prepared by the extension of the low temperature non equilibrium condition on the c axis sapphire. The thermal annealing of the materials was studied and the effects of in-situ oxygen doping and thermal annealing on the microstructure, chemical valence bond state and intermediate band luminescence characteristics were studied. It was found that the in-situ oxygen doping did not cause serious distortion of the lattice and even produced other material phases. The properties of the single crystal showed the preparation method of MOCVD. Technical advantage. Through the face cover annealing optimization method, the surface of ZnTe:O is effectively avoided and the crystal structure quality of the material is improved. At the same time, the intermediate energy band with oxygen and other electron traps is formed at the same time to 1.9eV, and the result is high with the result calculated with the non cross model. Optimization of the preparation conditions of MOCVD and the annealing treatment method It is beneficial to realize the transition from the non radiation compound to the extended state of the radiation compound, which is possible to improve the conversion efficiency of the ZnTe:O based middle band solar cells.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.055

【相似文献】