【作者】 袁国栋；

【导师】 叶志镇；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2006， 博士

【摘要】 近年来,宽禁带半导体材料ZnO的研究已经引起人们广泛的关注。ZnO是一种Ⅱ-Ⅵ族化合物半导体材料,具有直接宽带隙(室温下3.37eV),属于六方纤锌矿结构。由于ZnO具有较高的激子结合能(室温下为60meV),远大于室温热能(26meV),因而理论上会在室温下获得高效的紫外激子发光和激光。此外ZnO具有高熔点(1975℃),高热稳定性及化学稳定性;ZnO单晶薄膜可以在低于500℃的生长温度下获得,比GaN等其他宽禁带半导体材料的制备温度低很多,因此可以大大减少高温制备所产生的缺陷。另外,ZnO原材料资源丰富、价格低廉,对环境无毒无害,制备工艺简单,具有潜在的巨大商用价值。作为短波长发光器件、低阈值紫外激光器的一种全新的候选材料,ZnO已经成为当今半导体发光材料与器件研究中新的热点。 为了实现ZnO在发光器件领域的实际应用,必须外延生长晶体质量良好的p型以及n型薄膜,在此基础上,制备ZnO的同质pn结,进而通过掺入Cd、Mg调节ZnO禁带宽度,最终实现ZnO的量子阱和超晶格结构。ZnO中本征施主缺陷(Zn_i和V_o)的形成能很低,因此在实现ZnO的p型转变过程中,存在本征缺陷的严重补偿现象,同时,VA族和IA族元素尽管在理论上可以在ZnO中形成浅的受主能级,但是VA族元素中的N元素在ZnO中的固溶度低,其他的P、As、Sb原子半径大,引起大的晶格畸变和内应力;而IA族元素则很容易形成间隙态起施主作用。施主(Al)-受主(N)共掺杂方法实现ZnO良好的p型特性是近年来由我们浙江大学硅材料国家重点实验室叶志镇教授领导的课题组首先尝试并实现的。共掺杂方法可以一定的条件下提高受主杂质的浓度,从而有利于得到高空穴浓度的p型ZnO薄膜。 本文以利用Al-N共掺杂方法实现良好的p-ZnO薄膜作为研究的基础,以ZnO的p型掺杂机理为主要研究内容。深入分析了择优取向的ZnO多晶薄膜的生长机理,比较了多种常用的受主杂质在实现p型ZnO方面掺杂机理的异同,并对影响ZnO的p型特性的几个关键因素的作用机理作了深入研究。在实现ZnO的p型转变并深入分析其掺杂机理基础上,我们制备并研究了ZnO与Si的异质结及其接触特性,制备了ZnO的同质结、ZnO/ZnCdO异质结以及ZnO/Au的肖特基二极管的原型器件,并对其性能作了基础性研究。 C轴择优取向的ZnO薄膜的生长是一种自组装生长过程,在多种衬底上均更多还原

【Abstract】 In recent years, wide band gap semiconductor materials zinc oxide (ZnO) becomes to attract much more attention than ever before. ZnO is a kind of II-VI compound semiconductor with a wide direct band gap of 3.37 eV at room temperature (RT) and a hexagonal wurtzite structure. Its high exciton binding energy (60 meV at RT), which is much higher than RT heat energy (26 meV), will theoretically favor efficient UV excitonic emission processes at RT. In addition, ZnO has a high melting point (1975℃), high thermal and chemical stability. ZnO single crystal thin film can be obtained at a temperature under 500℃, which is much lower than GaN and other wide band gap semiconductors, so it can greatly reduce the defects formed in high temperature. Furthermore, ZnO is abundant, cheap, innoxious, easy to be prepared and with potential commercial value. As an important candidate of short-wave optoelectronic devices and low-threshold UV laser, ZnO has become a hotspot in the area of semiconductor optoelectronic devices.To realize the application of ZnO in optoelectronic devices, excellent epitaxy n-and p-type thin films are necessary. Based upon that, fabricating the ZnO homoj unction, band-gap engineering through Cd and Mg doping, and finally realized the quatum well and super lattice structure. The formation energy of the intrinsic defects (Zn;and Vo) is very low, so there is a heavy compensation in the p-type doping. At the same time, despite that the shallow acceptor energy in the group V and I, the solution of the group V element is very low. And other group V element, such as P, As, Sb, all has the large lattice mismatch with the substitution for the O atom in ZnO, which can lead to crystallinity distortion and in-plane stress. The group I element can easily form the interstitial state, and act as the shallow compensation donor. Donor (Al)-Acceptor (N) co-doping method is a good way to realize the p-type conduction in ZnO. Our research group, i.e., Professor Ye Zhi-Zhen group of state key laboratory of silicon materials is one of the earliest groups engaging in ZnO film studies. We first try and realize the co-doping p-type ZnO internationally. The co-doping method can increase the solution of the acceptor in fixed condition, so it can help to obtain the high hole concentration p-ZnO thin films.In this work, we’ve fabricated the p-type ZnO thin films with good electrical properties by the Al-N co-doping method, and we mainly focused on the p-type doping mechanism. Based on the deep investigation on the growth mechanism of C-orientation polycrystalline ZnO films, we’ve proposed the comparison of different acceptor dopants in p-ZnO doping, and analysis several important factor of affecting the p-type conduction. Based upon that, Si/ZnO heterojunction, ZnO-based pn junction, ZnO/ZnCdO heterojunction and ZnO/Au Schottky Barrier Diode have been successfully fabricated, and taken the fundamental research.The formation of the C-axis orientation ZnO thin films is a self-assembled process, and the preferential orientation can be obtained in many different kinds of substrates. It should be mentioned that various substrates can determine diverse formation mechanism. When grown on Si, it will preferential nucleate firstly;while in the case of glass, an amorphous ZnO layer initially forms. So, the crystal quality and electrical properties of the obtained ZnO thin films will depend on the substrate.We have fabricated the stable and reproducible p-ZnO based on the Al-N co-doping method using the DC Reactive Magnetron Sputtering. The as-deposited p-type ZnO thin films show an electrical property, such as resistivity of 20-30Q-cm, hole concentration of 1017-1018cm"3, and hall mobility of 0.5-1 cm2/V-s<= A moderate Al content is necessary for the p-type ZnO realization, instead of the higher or lower content both leading to n-type conduction. Due to the big size mismatch, in the suitable condition other group V elements are inclined to substitute the Zn place and at the same time induce two Zn vacancies, instead of the O place for the good p-type behavior. The active group I elements, such as Li and Na, can form the interstitial states, which always act as the shallow donors, compensate the hole concentration, and finally destroy the p-type properties. The III-V co-doping method can greatly promote the N solution in the ZnO thin films, and Al-N co-doping way is the best candidate.Substrate temperature (Ts) can provide the dynamic force of the nucleation, reaction and motivation during the growth process, responsible for the crystal quality and electrical properties. Higher or lower Ts are both unfavorable for the good as-received ZnO thin films. P-type ZnO can be realized in the range of 380°C-480°Cand 560°C-600°C, while n-type in others. We proposed the H passivationAl promotion combined activation model to explain the conduction type variation of n-p-n-p of Ts. The presentation of donor Al can sufficiently enhance the incorporation of N into the ZnO films. Using NH3 as the N source, the ZnO films show p-type when the oxygen partial pressure is 40% and 85%. In the instance of NO and NO2, all the ZnO thin films show n-type. The post annealing treatment under the O2 ambient can greatly improve the p-type properties, while the growth of high temperature buffer layer can obviously enhance the stability and reproducibility of the p-ZnO.Compared with the ZnO homoj unction, the double heteroj unction with n-ZnO/n-ZnCdO/p-ZnO exhibits a better rectifying characteristics, and reverse breakdown voltage can reach as high as 15V, and leakage current 10"6A. The n-ZnO/Au show a good Schottky contact property, while the barrier height is low and ideal factor is relatively high, due to the intrinsic defects and the surface states in the interface.更多还原