【作者】 薛书文；

【导师】 祖小涛；

【作者基本信息】 电子科技大学 ， 光学， 2007， 博士

【摘要】 ZnO具有较大的禁带宽度（3.3eV）和较高的激子束缚能（60meV）,与传统的宽带半导体材料GaN、ZnSe和SiC等相比,ZnO有许多优异特性,这使得ZnO在短波长发光二极管、激光器、探测器和太阳能电池等方面展现出诱人的应用前景。要使ZnO在光电器件领域获得广泛应用,关键的问题是制备出性能稳定优良的p型ZnO。在p型ZnO的掺杂中,N被认为是最好的受主掺杂物。但是,N在ZnO中的固溶度比较低,而且形成的受主能级也比较深,因此难以实现有效的掺杂。Ⅲ-Ⅴ族和Ⅱ-Ⅴ族共掺杂理论就是为解决这些问题而提出的,并且Ⅲ-Ⅴ族共掺杂理论已在ZnO的p型掺杂方面取得了可喜的研究成果。基于如上共掺杂的理论,本文尝试采用溶胶凝胶方法先制备出ZnO:Al和ZnO:Mg薄膜,使Al和Mg均匀掺杂在ZnO中,然后采用半导体技术中广泛采用的离子注入技术将高剂量N受主杂质掺杂到ZnO:Al和ZnO:Mg中,从而实现共掺杂的目的。基于这个研究构思,做了如下主要研究:1.详细研究了Al掺杂浓度和退火温度对ZnO薄膜结构、光学和电学性质的影响。研究结果显示,随着Al掺杂浓度（Al/Zn≤1%）的提高,ZnO:Al薄膜的（002）衍射峰强度和近紫外激子发光（NBE）强度不断增强,与缺陷相关的发光（DLE）强度不断减弱;基于Kramers-Kronig色散关系的计算表明,随着掺杂Al浓度的提高,ZnO:Al薄膜的吸收系数、折射率等不断减小。随着退火温度的提高（600-950℃）,ZnO:Al薄膜可见光区的折射率、吸收系数等逐渐增大,在紫外区却随着退火温度的提高而减小。另外也发现,在750℃以下退火时,ZnO:Al薄膜吸收边会随着退火温度的提高发生蓝移;在750℃以上退火时,薄膜吸收边随着退火温度的提高发生红移。ZnO:Al薄膜的光吸收在可见光区随着退火温度的提高逐渐增大,在紫外区随着退火温度的提高而减小。ZnO:Al薄膜的紫外峰强度随着退火温度的提高逐渐增强,而缺陷峰强度逐渐减弱。2.详细研究了Zn和Ge离子注入及退火温度对ZnO薄膜结构、光吸收和光致发光的影响。研究结果显示,Zn、Ge离子注入后,ZnO薄膜的衍射峰强度和荧光强度都显著降低,而可见光区的光吸收显著增强。退火温度对离子注入后的ZnO薄膜的结构和光学性质有显著影响,随着退火温度的提高,薄膜的结构和光学性质得到恢复。Zn离子注入后的退火结果显示,ZnO薄膜的结构在700℃退火后基本恢复到了离子注入前的状态,光致发光强度在600℃退火后基本恢复。Ge离子注入后的退火结果显示,ZnO薄膜的结构在600℃退火后基本恢复到离子注入前的状态,光致发光强度在800℃退火后基本恢复到离子注入前的状态。3.详细研究了N离子注入及退火温度对ZnO:Al和ZnO:Mg薄膜结构、光学和电学性质的影响。在共掺杂制备p型ZnO中,Al的掺杂含量对p型的转变很重要。实验结果证实,只有Al/Zn=I%的样品出现了明显的p型转变,样品在600℃退火30min后,Hall测试结果显示载流子浓度为1.6×10¹⁸cm^-3,空穴迁移率为3.76cm²/V·s。离子注入后的退火结果显示,ZnO:（Al,N）薄膜在600℃退火30min后结构和发光特性基本恢复到离子注入前的状态。N离子注入ZnO:Mg薄膜的实验结果显示,N离子注入后的ZnO:Mg薄膜在随后的退火温度过程中存在着显著的分解和蒸发行为。四探针测试结果显示,ZnO:Mg薄膜在N离子注入和随后的退火过程中一直呈高阻状态。更多还原

【Abstract】 Zinc oxide （ZnO）, an important II—VI semiconductor with a variety of good physical and chemical properties compared with conventional wide bandgap semiconductors such as GaN, ZnSe and SiC, is suitable for many applications like transparent conductors, lasers, UV detectors, and solar cells. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO. Though nitrogen has been believed to be most promising acceptor to dope p-type ZnO, low solubility in ZnO and deep impurity level cause significant resistance to the formation of shallow acceptor level and high acceptor concentration. Co-doping method was proposed to overcome these problems and has been widely accepted in experiments.In this paper, we had prepared ZnO:Al and ZnO:Mg thin films by sol-gel process and doped high-dose N ions into ZnO:Al and ZnO:Mg films by ion implantation technique which has been widely accepted in semiconductor industry. Based on the above experiments, we had obtained results as follows:1. Influences of Al doping concentration and annealing temperatures on the structural, optical and electrical properties were investigated. Results showed that the intensities of （002） diffraction peak and excitonic near band edge emission were increased with increasing doping concentration, while defect related emission was decreased. Results calculated from Kramers-Kronig relationship showed that the absorption coefficients and refractive indexes of ZnO:Al films were decreased with increasing Al doping concentration. With increasing annealing temperatures from 600-950℃, the absorption coefficients and refractive indexes of ZnO:Al films in the visible region increased, while decreased in the ultraviolet region. In addion, the absorption edge of ZnO:Al films blueshifted with increasing annealing temperatures from 600-750℃, while redshifted when the annealing temperature exceeded 750℃. The optical absorption of ZnO:Al films in the visible region decreased with increasing annealing temperature, while increased in the ultraviolet region. Near band edge emission increased with increasing annealing temperature, but defect-related deep-level emission decreased.2. Effects of Zn, Ge ion implantation and post-thermal annealing on the structural and optical properties of ZnO films were investigated. Results showed that the diffraction peaks and photoluminescence of ZnO films evidently decreased after Zn and Ge ion implantation. The optical absorption in the visible region increased after ion implantation. Post-thermal annealing had great influences on the structural and optical properties of ZnO films. With increasing annealing temperature, the structural and optical properties of ZnO films recovered. For Zn-implanted ZnO films, the structural properties recovered after annealing at 700℃for 1 h and photoluminescence recovered after annealing at 600℃for 1 h. For Ge-implanted samples, the structural properties of ZnO films recovered after annealing at 600℃for 1 h, and the photoluminescence recovered after annealing at 800℃for 1 h.3. Effects of N-ion-implantation and annealing temperature on the structural, optical and electrical properties of ZnO:Al and ZnO:Mg films were investigated. Al contents played a very important role in preparation of p-type ZnO. Our experimental results showed that only those samples with Al/Zn=1% turned into p-type conduction. After annealing at 600℃for 30 min, Hall measurement results showed that the carriers’ concentration and mobility were 1.6×10¹⁸cm^-3 and 3.76cm²/V·s, respectively. Post-thermal annealing had pronounced influences on the structural and optical properties of ZnO:（Al, N） and ZnO:（Mg, N） films. Annealing results showed that the structural and optical properties of ZnO:（Al, N） recovered after annealing at 600℃for 30 min. For ZnO:Mg films, we found evident decomposition and evaporation behavior during annealing at 600-900℃. Four-point probe resistivity measurements showed that ZnO:（Mg, N） films exhibited high resistivity after annealing at different temperatures.更多还原