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1、浙江大学硕士学位论文 1 摘摘 要要 ZnO 是一种极具应用潜力的直接宽禁带半导体材料， 室温禁带宽度为 3.37eV, 近年来， ZnO 作为宽带半导体材料的研究越来越受到人们的重视。 与其它宽禁带 半导体材料相比，ZnO 具有许多优点，自由激子结合能高达 60meV, 薄膜生长温 度低，抗辐射性好，受激辐射有较低的阈值功率和很高的能量转换效率，这些优 点使 ZnO 有望在短波长发光二极管、激光器、探测器和太阳能电池等众多领域 获得广泛的应用。 ZnO 实用化的前提是制备出性能优良的 p 型和 n 型材料， 本征 ZnO 呈 n 型导电性，通过掺 Al、Ga、In 等元素，人们已经很容易实现
2、 ZnO 的 n 型掺杂。 但是 ZnO 的 p 型掺杂十分困难， 这是由于受主元素在 ZnO 中固溶度低、 受主能级深以及本征施主缺陷高度的自补偿效应等缘故。p 型掺杂的困难限制了 ZnO 的进一步应用。一些研究者通过族和族元素掺杂制备出了 p 型 ZnO 薄 膜，但是或者载流子偏低，电阻率偏大，或者性能不稳定。N 由于在 ZnO 中较 浅的受主能级成为 ZnO p 型掺杂的首选掺杂剂。 但是 Yamamoto 通过计算表明 N 的掺入会使 ZnO 薄膜晶体的马德隆能升高， 导致 N 在 ZnO 中掺杂浓度低和不稳 定。理论预测表明，如果受主和施主按 2：1 的原子比同时掺入 ZnO 中会降
3、低马 德隆能量，大幅促进受主在 ZnO 中掺杂浓度，并且掺杂后的 ZnO 性能稳定。根 据这一思路， 作者利用直流反应磁控溅射技术， 在 N2O-O2混合气氛中， 采用 Al-N 共掺的方法成功制备出了 p 型 ZnO 薄膜，利用 X 射线衍射（XRD） 、场发射扫 描电镜（FESEM） 、透射光谱、Hall 测试仪等方法对 ZnO 薄膜的结构和性能进行 了表征，系统研究了靶材中 Al 含量、衬底温度、气氛中 N2O 分压比等生长条件 对其性能的影响。结果表明，Al-N 共掺方法制备的 ZnO 薄膜表现出优良的沿 （002）方向的择优取向性，表面较平整，粒度均匀，厚度约 270nm。和单独掺
4、N 相比，采用共掺方法能大幅提高 p 型 ZnO 的空穴浓度，降低薄膜的电阻率。 当靶材中含 Al 0.4at%，衬底温度 500，在纯 N2O 气氛中制备的 p 型 ZnO 薄膜 性能最好， 载流子浓度最高为 1.3 10 18 cm 3， 同时电阻率最低为 54 cm。Al-N 共掺 p 型 ZnO 载流子迁移率较低， 这可能是 N 和 Al 的同时掺入引起严重的电离 杂质散射和较差的晶体质量共同作用的结果，如果能够大幅改善 ZnO 薄膜晶体 的质量，我们就可以通过共掺的方法制备出载流子浓度高且迁移率较高、电阻率 低的 p 型 ZnO，为 ZnO 真正实现广泛应用奠定良好的基础。 浙江大学
5、硕士学位论文 2 Abstract Zinc Oxide with a direct wide bandgap of 3.3 eV at room temperature has recently attracted considerable attention because of its many potential applications. Comparing with other wide bandgap semiconductor materials, ZnO has many promising advantages: ZnO has large excitonic bindin
6、g energy(60meV at RT), which promises strong photoluminescence from bound excitonic emissions at room temperature; it is more resistant to radiation damage; high- quality ZnO with very low defect densities can be synthesized at relatively low temperature. For these advantages, ZnO is promised to be
7、widely used in the photoelectricity devices such as UV light-emitting diodes ( LEDs ) and lasers. To realize such optoelectronic devices, it is required to control the electronic properties, such as the nature of conduction as well as its carrier density and mobility. The naturally occurring ZnO has
8、 n-type conductivity which can be enhanced by doping with group- elements ( Al, Ga, etc. ). However, ZnO has suffered from one major disadvantage: the lack of good, reliable, p-type material. There are several possbile reasons for this dilemma: (1) lack of shallow-acceptor dopants; (2) low solubilit
9、y of such dopants; and (3) compensation by increased levels of impurity and native defect donor species. Several groups have achieved p-type ZnO with group-or group- elements, but it either had low carrier concentration and high resistivity, or was unstable. Theoretical calculations of the electroni
10、c band structure predicted that nitrogen is the best candidate for producing a shallow acceptor level in ZnO. But N doping increases the Madelung energy of ZnO, which resulting in the instability of the ionic charge distributions. The codoping method using acceptors and reactive donors in the ratio
11、of 2:1 simultaneously was proposed to increase the solubility of nitrogen in ZnO and decrease the Madelung energy, On the basis of this idea, p-type ZnO was prepared in N2O-O2 atmospheres by Al-N codoping method using DC reactive magnetron sputtering in this paper. The structure and properties are c
12、haracterized by XRD, SEM, Transmission spectra and Hall. Effects of growth parameters, such as substrate temperatures and Al contents in sputtering targets, on the properties of as-grown co-doped ZnO were investigated. Results indicate that co-doped ZnO films with a thickness of about 270nm exhibit
13、polycrystalline structure with the preferential orientation of (002) plane, smooth dense surface, and good grain size uniformity. Compared with N doping alone, Al-N co-doped p-type ZnO films have greatly higher carrier concentration and lower resistivity. 浙江大学硕士学位论文 3 The best result is: the highest
14、 carrier concentration of the as-grown ZnO is 1.3 10 18 cm 3，with the lowest resistivity of 54 cm. The low carrier mobility of the co-doped ZnO is likely due to the scattering of ionic impurity and the poor crystal quality of ZnO. If we can improve the crystal quality of ZnO, the carrier mobility of
15、 the co-doped ZnO will greatly increase, thereby p-type ZnO with high carrier concentration and low resistivity can be realized using co-doping technique. 浙江大学硕士学位论文 4 目目 录录 摘 要.1 Abstract.2 目 录4 第一章 文献综述7 1.1 ZnO 的性质及应用7 1.2 ZnO 薄膜的制备技术.8 1. 2. 1 电子束蒸发.8 1.2.2 溅射法.9 1.2.3 脉冲激光沉积（PLD）10 1.2.4 金属有机化学
16、气相沉积（MOCVD）11 1.2.5 分子束外延（MBE）.12 1.3 ZnO 的研究进展.13 1.3.1 ZnO 发光性能研究.13 1.3.2 ZnO 薄膜中的本征点缺陷17 1.3.3 p 型 ZnO 的研究进展.20 第二章 直流反应磁控溅射原理29 2.1 气体辉光放电原理.29 2.2 溅射产额30 2.2.1 入射离子能量31 2.2.2 离子入射角度31 2.2.3 靶材温度.32 2.3 溅射粒子的能量32 2.3 磁控溅射原理.34 第三章 Al-N 共掺制备ZnO薄膜实验介绍.36 浙江大学硕士学位论文 5 3.1 S 型枪直流反应磁控溅射设备.36 3.2 溅射靶材37 3.3 ZnO 薄膜生长衬底（基片）的选择和清洗.38 3.4 S 型枪直流反应磁控溅射制备 ZnO 薄膜的过程38 3.5 ZnO 薄膜物理性能测试.40 第四章 共掺与非共掺ZnO薄膜的比较.41 4.1 电学性能比较.41 4.2 光学性能比较.42 4.3 Al-N 共掺 ZnO 薄膜 SIMS 分析.43 4.4 小结.44 第五章 衬底温
