【作者】 钟声；

【导师】 傅竹西；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2008， 博士

【摘要】 近年来,ZnO材料以其在短波长发光器件、压电传感器、透明导电极、太阳能电池以及表面声波器件等领域的广泛应用,吸引着人们越来越多的关注。ZnO具有3.37eV的禁带宽度,与同为宽禁带半导体的GaN相比,ZnO具有更高的激子束缚能、更好的稳定性以及更低廉的制备成本,这些优势使得最近10年来对ZnO的研究日益升温。同时,我们也注意到当前制约ZnO发展的一个难题,那就是稳定的可重复的p型ZnO的制备。尽管最近几年人们在ZnO的p型掺杂方面取得了很多进展,但是距离实际应用尚有一定的差距。同时,对于未掺杂ZnO的理论研究,包括生长条件、缺陷类型以及发光机理等问题还缺乏足够深入的探索。基于上述背景,本论文围绕着材料生长、结构形貌、光电特性以及p型掺杂等方面,开展了一系列工作,具体可分为如下几个方面:1.在磁控溅射设备上制备了高取向的ZnO薄膜,研究了衬底温度、生长气氛和溅射功率等参数对薄膜结构和形貌的影响,在优化的生长条件下实现了Si基ZnO薄膜的高质量生长;利用变温PL光谱,详细分析了未掺杂ZnO薄膜在低温下的光致发光特性,确认了各发光峰的来源;计算的结果表明,低温下占主导地位的中性束缚激子复合发光很可能来自于H杂质。2.研究了热退火对ZnO薄膜结构和光电特性的影响。透射和吸收光谱的测量表明,800℃下氧气退火能够有效地提高薄膜的可见光透过率和光学带隙;XPS分析发现,退火后薄膜中的O空位明显减少,薄膜组分更符合理想化学计量比:Ⅰ—Ⅴ特性测量表明,ZnO/Si异质结在退火之后具有更好的二极管整流特性。因此,适当的后期退火能提高ZnO薄膜的光学和电学性能。3.研究了Al₂O₃过渡层对ZnO薄膜结构形貌和发光特性的影响。XRD和GIXRD的结果表明,过渡层的引入能有效地减小ZnO薄膜与Si衬底间的失配,使得ZnO薄膜中的应力充分弛豫;AFM表面分析可以看出,过渡层上生长的ZnO薄膜粗糙度明显降低,更趋向于二维平面生长模式;比较PL光谱发现,过渡层能够增加ZnO薄膜的激子复合几率,提高其紫外发射强度。这些结果表明,Al₂O₃过渡层大大提高了Si基生长ZnO薄膜的晶体质量。4.采用热氧化法制备了ZnO∶N薄膜,分析了后期退火温度对掺杂薄膜结构形貌和光电特性的影响,发现N在掺杂薄膜中有施主和受主两种状态,通过退火温度的变化,可以控制N受主的形成;通过ZnO∶N薄膜的变温PL光谱,计算出N在ZnO中的受主能级位置;ZnO同质结的Ⅰ—Ⅴ整流特性表明ZnO∶N薄膜有转化成p型的趋势。我们的结果为进一步获得p型ZnO材料提供了理论依据和宝贵经验。更多还原

【Abstract】 In recent years, ZnO has gained substantial interest for its wide applications in short wavelength photonic devices, piezoelectric sensors, transparent conducting films, solar cells and surface acoustic wave devices. Compared with another wide bandgap semiconductor GaN, ZnO has a higher exciton binding energy, better stability and lower cost of production, which has made ZnO experiencing a research boom in the last ten years.At the same time, we also note that the development of ZnO based devices is hindered by lack of reliable and reproductive p-type ZnO. Though much progress has been made by researchers in recent years, there are still some obstacles standing on the way to commercial application of p-type ZnO. In addition, there remains much controversy regarding the intrinsic defects of undoped ZnO. Considering the above background, this dissertation focused on the aspects of crystal growth, structural morphology and p-type doping. The contents can be divided into the followings:1. Under optimal growth conditions, highly oriented ZnO films were prepared using DC magnetron sputtering method. The structural, morphological, optical and electrical properties of undoped ZnO films were investigated. By low temperature PL measurement, the temperature dependence of the optical properties of ZnO films was discussed. The results show that the dominant peak of D°X transition is probably originated from hydrogen.2. Effects of the annealing temperature of ZnO films on the structural and optoelectronic properties were studied in detail. XRD results reveal that post annealing processing can improve the film’s quality. XPS shows that ZnO films are well closed to stoichiometry after annealing at 800℃in oxygen ambient. Absorption Spectra reveal the annealed films are of high optical properties. The I-V characteristics show that ZnO/Si heterojunction annealed at 800℃near ideal diode rectifying behavior. 3. Effects of Al₂o₃ buffer layer on the properties of ZnO films were investigated. By introducing Al₂o₃ buffer layer, the mismatch between Si substrates and ZnO films can be effectively reduced and relaxation of the stress is observed. In addition, the Al₂o₃ buffer layer enhances the intensity of UV emission from ZnO films.4. Nitrogen doped ZnO films were realized by thermal oxidation of the Zn₃N₂ films. The relationship between the structural and optical properties of the ZnO:N films and annealing temperature was investigated. XRD results illustrate that the as sputtered Zn₃N₂ films can be transformed into ZnO:N films after annealing at 600℃. XPS results reveal that nitrogen has two chemical states in the ZnO:N films: one is （N₂）_o. donor and the other N_o acceptor. Hall effect measurements demonstrate the decrease of the carrier concentration in the ZnO:N films. FA and DAP transition peaks are observed in low temperature PL spectra of ZnO:N films, from which the nitrogen acceptor binding energy can be obtained. The rectifying characteristics of I-V measurement derived from ZnO homojunctions indicate that the ZnO:N films exhibit a tendency of converting to p-type. Our results provide a theoretical basis and valuable experience.更多还原