【作者】 马德伟；

【导师】 叶志镇；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2003， 博士

【摘要】 ZnO及其合金由于具有宽的直接带隙，在紫蓝光发光二极管和激光二极管等光电器件方面具有非常广阔的应用前景。ZnO和GaN有相同的晶体结构和相似的晶胞参数和带隙宽度，但具有比GaN更高的激子束缚能，因此更容易在室温或更高温度下实现高效率的受激辐射，同时具有较低的阈值电压。ZnO中引入Cd组分，形成Zn_1-xCd_xO合金半导体，可以实现发光波长从紫外光波段变化到蓝光甚至绿光波谱范围；而且在固溶范围内，Zn_1-xCd_xO合金的晶体结构和晶胞参数变化不大，这为制备ZnO／ZnCdO异质结、超晶格及量子阱等结构提供了有利条件，因此Zn_1-xCd_xO合金半导体的研究具有非常重要的意义。 目前国际上关于Zn_1-xCd_xO薄膜的研究还比较少，且薄膜的结晶质量都很差，类似于非晶相或具有多相结构。我们硅材料国家重点实验室叶志镇教授研究小组是国内最早开展ZnO方面研究的单位之一，在ZnO薄膜晶体的生长、p型掺杂及ZnMgO合金半导体等方面都取得了一些成果。鉴于ZnCdO合金半导体在ZnO基半导体器件方面亦具有潜在的重要研究价值，本课题特从事此方面的研究，现介绍如下： 我们以Si（111）、蓝宝石及玻璃等为衬底溅射沉积了Zn_1-xCd_xO（O≤x≤1.0）薄膜，系统研究了温度、组成等参数对薄膜晶体结构的影响。研究表明，溅射沉积Zn_1-xCd_xO（0≤x≤0.6）薄膜的优化工艺生长参数分别为：衬底温度450℃，溅射功率40～60W，溅射气压3～5Pa，且Ar／O₂=1／4。并且发现，当x≤0.6时，薄膜为高度c轴择优取向的单相合金固溶体；x=0.8时，薄膜发生明显分相；x=1.0时，薄膜亦具有高度择优取向。首次获得合金薄膜的室温和低温PL谱，从而证实薄膜是单相晶体发光；随着Cd组分含量的增加，薄膜发光峰向长波方向移动，从376nm（x=0）变化到414nm（X=0.6），为进一步研制ZnO基蓝光光电器件奠定了基础；对合金薄膜能带工程从理论方面进行了深入研究，提出了固溶范围内其带隙E_g与Cd组分含量x之间的关系：E_g（x）=3.29664-1.21687x+1.25539x²（0≤x≤0.53），而其晶胞参数c与Cd组分含量x之间的关系符合Végard定律：c（x）=0.5229+0.00357x。初步提出了发光谱中黄绿光的发光机制，认为它主要与V_o⁺缺陷能级与V_Zn^-，V_Cd^-和O_i^-等缺陷能级之间的电子跃迁有关，其它如Zn_i、Cd_i、O_Zn、O_Cd等缺陷可能对黄绿发光有次要影响。 确定薄膜实际组成是合金薄膜研究的基本和重要任务，借助于XPS测试，我们发现，溅射沉积的Zn_1-xCd_xO（0≤x≤1.0）薄膜组成与靶材组成基本保持一带隙可调的znl一CdxO合金半导体薄膜的研究致，且薄膜中Zn、Cd元素均以氧化态存在;籍SIMS测试，我们发现了Cd组分易在薄膜与硅衬底界面处发生偏聚的现象，而薄膜中Zn、O组分随深度变化分布均匀，且Zn、Cd在薄膜表面均基本无偏析现象。 我们研究发现了Zn，一xCdxO薄膜电阻率随Cd组分变化发生突变的现象，当cd组分含量x切.4时，znl_xCdxo薄膜的电阻率在1 03身cm数量级以上，自由电子浓度在10’5一10’“/c厅数量级，薄膜近似为绝缘体;cd组分含量为60%左右时，薄膜电阻率陡然下降为0.422Q·cm，同时其自由电子浓度骤增至一101即cm3，我们对此也作了解释;Cd含量继续增加时，薄膜电阻率亦随之降低，自由电子浓度则持续增加，应0.8时，薄膜近似为导体。 衬底对薄膜的结晶质量具有非常重要的影响，我们发现:蓝宝石上沉积的薄膜具有最优的结晶质量，硅衬底次之，玻璃由于为非晶态，在其上沉积的薄膜结晶质量最差。 为了进一步提高薄膜的结晶质量，我们对znl一CdxO（O夕夕.0）薄膜作了退火处理，并且发现:300℃退火可基木消除原位沉积薄膜的内应力，减少薄膜内部的品体缺陷，但其结品质量提高不大;500℃下退火的薄膜具有最高的XRD强度，但Cd组分含量较高(、七仪6、的薄膜易发之!:CdO绍分的相偏析和再蒸发现象;薄膜在500℃一下的退火时间一般不易超过lh，而且退火气氛应选择02气氛。 总之，我们本课题的研究无论在国内还是在国际均处于领先水平，为Zn，一CdxO合金半导体薄膜的进一步研究奠定了基础。更多还原

【Abstract】 ZnO and its alloys have extensive prospects in the applications of optoelectronic devices such as ultra-violet (UV)/blue light-emitting diodes and laser-diodes due to wide direct band-gaps. Though having the same crystal structure as GaN together with the similar cell parameters and band-gap, ZnO exhibits a much larger excitonic binding energy than GaN, so it is easier to realize effective stimulated radiation at room temperature (RT) and higher temperatures, accompanied by a low threshold voltage. By introducing Cd content into ZnO, Zn1-xCdxO alloy semiconductors can be formed, and the luminescence of the alloys can be red-shifted to blue, even green light spectra from UV spectrum. More important, in the soluble range, the crystal structures and cell parameters of Zn1-xCdxO alloys change very little, this is advantageous for preparing ZnO/Zn1-xCdxO heterojunction, superlattice and quantum wells etc. Therefore, it is of great significance to investigate on Zn1-xCdxO alloy semiconductors.Presently, studies on Zn1-xCdxO films were very little, and the crystal quality of the prepared films was very poor, analogical to amorphous state or multi-phase states. 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. Till now, we have made great progresses in the growth of ZnO film, ZnO p-doping and investigations on ZnMgO alloy semiconductors etc. Considering that ZnCdO alloy semiconductor also has potentially great values in ZnO-based semiconductor devices, so we decided to carry out this research, now we outline it as follows:By the dc reactive magnetron sputtering method, we have deposited Zn1-xCdxO (0≤x≤1.0) films on Si(111), sapphire and glass substrates, and systemically investigated the effects of growth parameters such as substrate temperatures, compositions on the film crystal structures. Results show that the optimal growth parameters for depositing Zn1-xCdxO (0≤x≤0.6) films are: substrate temperatures of 450℃ , sputtering powers of 40-60 W, sputtering pressures of 3~5 Pa with the argon to oxygen ratios of 1:4. Moreover, we noted that for x≤0.6, the films are of single-phases with highly c-axes preferred orientations; for x=0.8, distinct phase separations were observed; for x=l .0, the film also has a highly preferred orientation.For the first time, we successfully obtained the PL spectra of the alloy films, and testified that the luminescence arose from single phased crystals. With increasing Cd contents, the PL peaks of the films are red-shifted to 414 nm (x=0.6) from 376 nm (x=0), it establishes a good foundation for developing ZnO-based blue light devices. Theoretically we investigated the band-gap engineering of the alloy film in detail, and gave a formula between band-gap (Eg) of alloy film and Cd content (x), Eg(x)=3.29664-1.21687x+1.25539x2 (0≤x≤0.53). However, the relationship between the band-gap and the Cd content accords with Vegard law, c(x)=0.5229+0.00357x. Furthermore, we put forward an elementary model to explain the green-yellow luminescence from the film, and considered that it is mainly related to electron transitions from the single ionized oxygen vacancies (V0+) to Zn, Cd vacancies (Vzn-, VCd-), or oxygen interstices (00, other intrinsic defects such as Znj, Cdj, Ozn, OCd etc, may also play minor roles in the green-yellow emissions.Determining film compositions plays fundamental and important rules in studying alloy films. By XPS measurements, we observed that the Cd/Zn ratios in the Zn1-xCdxO (0≤x≤1.0) films were almost the same as in targets, and the Zn, Cd atoms were all in oxidized states. By SIMS measurements, we found a phenomenon that the Cd content can easily accumulate at the interface between the film and Si substrate, however, the Zn and O components can distribute uniformly with the film depth variations, and the Zn and Cd components have nearly no segregations at the film surface.We found that the electrical resistivity of the Zn1-xCdxO (0≤x≤更多还原