【作者】 孙剑；

【导师】 白亦真； 张庆瑜；

【作者基本信息】 大连理工大学 ， 凝聚态物理， 2008， 博士

【摘要】 金刚石膜化学气相沉积（CVD）技术发展日趋成熟,CVD方法得到的金刚石膜与天然金刚石膜性能相差无几,且制备成本相对较低,因此具有广阔的应用和商业前景。本文以CVD方法制备的自持金刚石厚膜为基片,沉积压电薄膜并系统研究了压电薄膜的各项性能。压电薄膜/自持金刚石厚膜结构可以用于制备声表面波（SAW）器件,此结构既利用了金刚石最高表面声速的性能,又可以充分利用金刚石最高热导率的特性,从而使器件具有比常规器件更优异的性能。在具体的沉积工艺中,选择较平整的金刚石成核面作为功能薄膜的沉积表面,可以大大降低金刚石基板机械抛光的困难。通过这种简单的工艺方法,在自持金刚石厚膜（FTDF）的成核面上制备了性能良好、达到应用要求的压电薄膜,为进一步的器件制备和应用打下了良好的基础。本文采用三种方法在自持金刚石厚膜上制备了ZnO和GaN薄膜,主要通过“如何在这种特殊的衬底上得到性能良好的压电薄膜这一主题”开展了系统的研究工作。工作内容主要分三个部分,结论如下:1、利用超高真空磁控溅射系统在自持金刚石厚膜上沉积ZnO薄膜,研究发现:（1）随着基片温度的升高,FTDF上ZnO薄膜的晶体质量有所提高,这与硅片上沉积的ZnO薄膜的变化趋势稍有差异。FTDF和硅片上表面形貌的变化趋势相一致,也都得到了较高的基片温度下,样品紫外发光较强的结论。因此说明基片温度对FTDF上ZnO薄膜的性能有决定性的影响,FTDF衬底的影响较小。（2）其他工艺条件,比如:射频功率、工作气压和氧气流量变化对FTDF上ZnO薄膜的结晶性能、表面形貌和发光性能的影响不大,ZnO薄膜性能的差异主要与基片本身所含缺陷和晶界相对较多密不可分。（3）经检测FTDF上沉积的所有样品均为高阻,符合SAW器件的要求。（4）FTDF上沉积ZnO薄膜的多取向成核机制以及表面团簇的形成机制表明FTDF基片表面对沉积ZnO薄膜的性能有重要影响。2、利用等离子体增强MOCVD系统在自持金刚石厚膜上沉积ZnO薄膜,研究发现:（1）工作气压为38 Pa、基片温度为600℃的条件下在FTDF上得到了较高c轴取向的未掺杂的ZnO薄膜。其表面岛状团簇密度一致,有很清晰的边界,没有明显的起伏,表面平整。（2）基片温度从500℃升高到700℃时,FTDF上N掺杂ZnO薄膜的结晶特性、表面形貌特性和光学特性均有所下降。这主要是由于温度升高引发的结构缺陷增多引起的,并通过低温变温光谱发现的与结构缺陷有关的激子发光峰增多的现象证实。基片温度为500℃时样品具有较为平整的表面、较高的结晶质量、较强的紫外发射、较高的电阻率、相对较高的Zn/O原子比和较高的Zn-O结构的相对含量。（3）FTDF上未掺杂ZnO薄膜合适温度区间的存在主要是化学反应和表面原子脱附共同作用的结果,FTDF上N掺杂ZnO薄膜晶粒尺寸减小则与N₂O引入有一定关系。3、利用电子回旋共振MOCVD系统在自持金刚石厚膜上沉积GaN薄膜,研究表明:N₂富足的气氛有利于GaN薄膜（101）方向择优生长和表面团簇的长大。不同N₂流量下得到的样品表面岛状团簇均匀,平整度非常高,可以预期以此制备的SAW器件会具有较低的插入和传输损耗。更多还原

【Abstract】 Recently,study of Chemical Vapor Depostion（CVD） diamond films is going maturity. CVD diamond films have excellent characteristics nearly the same as natural diamond while with much lower cost.Therefore,CVD diamond films have a very bright future in their application and the market.In this dissertation,Freestanding Thick Diamond Films（FTDF） prepared by CVD method are applied as substrates of piezoelectric materials and the piezoelectric films are investigated systematically.Piezoelectric films/FTDF can be used as substrates of Surface Acoustic Wave（SAW） devices,which can make full use of the highest SAW velocity and heat conductivity of diamond.So,piezoelectric films/FTDF structure SAW devices can be expected to be more excellent than conventional devices.In the deposition technique,the use of smooth nucleation side of FTDF avoids the tedious task of diamond polishing.With this simple method, piezoelectric films of high quality on FTDF were prepared,which can meet the requirement of application and would lead to the elaboration of high quality and high power durability SAW devices in the future.In this work,ZnO and GaN films were deposited on FTDF by three different methods and how to prepare piezoelectric films of high quality on the special substrates has been studied systematically.The results mainly in three parts are summarized as follows:1 ZnO films were deposited on FTDF by the reactive radio-frequency magnetron sputtering method.（1） The results demonstrate that the crystalline quality of ZnO films on FTDF can be improved with substrate temperature increasing,which is slightly different from the tendency on silicon.The surface morphology tendency of ZnO films on FTDF is accorded with the tendency on silicon.Higher substrate temperature can lead to stronger Ultraviolet（UV） emission of ZnO films.Substrate temperature plays a key role on the quality of ZnO films on FTDF while FTDF has little effect at the same time.（2） Other process conditions,such as radio-frequency power,working pressure and O₂/Ar ratio,have little influence on the crystalline quality,surface morphology and optical property of ZnO films on FTDF,while the defects and grain boundary of FTDF are closely related with the quality of ZnO films deposited on FTDF. （3） All the samples are of high resistivity,which can meet the requirement of SAW devices.（4） Multi-orientation texture and cluster development mechanism of ZnO films on FTDF indicate that characteristics of ZnO films are closely related with surface of FTDF.2 ZnO films were deposited on FTDF by plasma enhanced MOCVD system.（1） Highly c-axis-oriented undoped ZnO films on FTDF are obtained at 38 Pa and 600℃with a strong UV emission.The ZnO grains are of uniform density with clear boundaries and a clean surface.（2） With substrate temperature increasing from 500℃to 700℃,the morphological, crystalline and optical qualities of N-doped ZnO films tend to decline,which maily result from the increase of structural defects induced by high temperature.From variable temperature PL spectra,it can be proved by the increase of emission of exciton bound related with structural defects.The sample at 500℃has a cleaner surface,narrower FWHM,higher resistivity and stronger PL intensity with a relatively higher Zn/O atomic ratio and relatively more Zn-O bond structure.（3） Both chemical reaction and surface atom diffusion render an appropriate substrate temperature for ZnO films on FTDF.The grain size of N doped ZnO films decreases with substate temperature increasing,which may be due to the increase of chemical active O^2-. induced by N₂O.3 GaN films were deposited on FTDF by Electron Cyclotron Resonance MOCVD （ECR-MOCVD） system.N₂ affluent atmosphere may lead to GaN film growth in a preferred orientation and a very smooth surface with larger clusters.GaN films with different N₂ flowrates have a very smooth surface with a probability of the fabrication of SAW device with a lower insertion and transmission loss.更多还原