【作者】 孙剑；

【导师】 白亦真；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2008， 硕士

【摘要】 ZnO是一种新型的直接带隙宽带半导体，室温禁带宽度约为3.37eV，具有较大的激子束缚能（60meV），可以实现室温紫外激光发射。作为新一代的宽带半导体材料，以其优异的电学、光学、压电等性能，在发光二极管、光探测器、声表面波（SAW）器件等诸多领域有着广泛的应用。工作频率超过1GHz的SAW器件在今后高频无线电通讯中具有极其广泛的需求。但是工作频率超过2.5GHz的声表面波滤波器，对叉指换能器电极宽度的要求将达到传统光刻技术的极限。ZnO／金刚石结构的声表面滤波器可以充分利用ZnO的压电性和金刚石最高弹性刚度系数以及最高声速的优异性能。ZnO／自持金刚石厚膜这种结构作为SAW器件的基片，既能避免其他基片带来的散热差的缺点，又可以充分利用金刚石的优异性能。选择较光洁的成核面作为功能表面还可以大大降低机械抛光的困难，同时这种简单的方法有利于获得高质量、高功率持久性的SAW滤波器。本文用超高真空磁控溅射设备在不同参数下于自持金刚石厚膜上沉积了ZnO薄膜，并利用X射线衍射（XRD）仪，扫描电镜（SEM），电子探针（EPMA），光致发光（PL）光谱和霍尔测量系统对样品进行了检测。结论如下：Ⅰ不同沉积温度下ZnO的特性分析（ⅰ） XRD表明随着沉积温度的升高，ZnO薄膜的晶体质量有所提高。（ⅱ） SEM结果表明：在基片温度从300℃升高到600℃的过程中，薄膜表面上岛状团簇变小，粗糙度降低；在基片温度从600℃升高到750℃时，岛状团簇变大，粗糙度有所升高。（ⅲ）基片温度为750℃的PL谱表明，高温条件有利于ZnO薄膜的光学性能的提高，此时由EPMA测得的薄膜中Zn／O成分比接近ZnO的化学计量比。（ⅳ）霍尔测量表明样品均呈现出高阻状态，满足声表面波滤波器的制备条件。Ⅱ不同Ar／O₂比条件下ZnO的特性分析（ⅰ） XRD表明随着氧分压的增大，ZnO薄膜的晶体质量趋于下降。（ⅱ） PL谱测量表明，随着氧气流量的增加，PL谱强度先增后减，半高宽的值先减后增，其峰位基本不变。并且分析表明在优化的氧分压条件下（Ar／O₂≈1），样品的发光性能最好，具有较低的内部缺陷，会相应降低SAW滤波器的插入损耗和传输损耗。（ⅲ）霍尔测量表明样品均呈现出高阻状态，满足SAW滤波器的制备条件。Ⅲ不同射频功率条件下ZnO的特性分析（ⅰ） XRD，PL谱，EPMA结果表明在射频功率为70W的条件下，样品具有最好的结晶性能，最强的PL谱强度以及最高的Zn／O含量。（ⅱ） SEM表明样品表面较平整，这是SAW器件获得较高的机电耦合系数的必要条件。（ⅲ）霍尔测量表明样品均呈现出高阻状态，符合SAW滤波器的要求。更多还原

【Abstract】 ZnO is a novel direct band-gap semiconductor （Eg=3.3eV at RT） with a high exciton binding energy of about 60meV. The feasibility of using excitionic lasers of ZnO at RT has been demonstrated. There has been an increasing interest in ZnO due to its electrical, optical and piezoelectric properties making suitable for many applications such as light emitting diodes, photodetectors, surface acoustic waves device and so on. SAW filters with working frequency higher than 1GHz will be widely applied in the intending wireless communication, whereas higher resonant frequencies （superior to 2.5GHz） tend to push the limits of conventional photolithography. ZnO/diamond structure as SAW substrates offers an attractive means for relaxation of the lithographic criteria since ZnO has excellent piezoelectricity while diamond has the highest elastic and stiff coefficient and highest sound velocity. ZnO/Freestanding Thick Diamond Films （FTDF） layered structure without additional substrates can avoid restriction of heat dispassion while making full use of the outstanding characteristics of diamond. The use of smooth nucleation side of FTDF avoids the tedious task of diamond polishing and this simple method would lead to the elaboration of high quality and high power durability SAW devices.In this work, ZnO films are deposited on FTDF by the reactive radio-frequency magnetron sputtering method. The properties of ZnO films are systematically investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, electron probe microanalysis （EPMA）, photoluminescence （PL） spectra, and Hall measurements. The results are as follows:I Properties of ZnO Films at Various Substrate Temperatures（i） The XRD patterns demonstrate that the crystalline quality of ZnO films tend to increasewith the increase of substrate temperature.（ii） The SEM and measurement shows that with the increase of substrate temperature from 300℃to 600℃, the surface islands of ZnO films tend to become smaller and the surface roughness decreases. With the increase of substrate temperature from 600℃to 750℃, the surface islands of ZnO films tend to become larger and the surface roughness increases.（iii） The PL spectra at the substrate temperature of 750℃demonstrate that high substrate temperature has benefit for the optical properties of ZnO films. The sample at the substrate temperature of 750℃is near the stoichiometry of ZnO characterized by EPMA.（iv） The Hall Effect measurement shows that the samples have high resistivity, which can meet the requirements of SAW devices.II Properties of ZnO Films at Various Radio-frequency Power（i） The XRD patterns demonstrate that the crystalline quality of ZnO films tend to decrease with the increase of partial pressure of Oxygen.（ii） The PL spectra demonstrate that the intensity of PL spectra increases and then decreases, the FWHM decreases and then increases with the peak of 376nm. The results indicate that the ZnO film with an optimal ratio of O₂/Ar≈1 is has the best optical property with low internal defects, which are expected to decrease the insertion and transmission loss for the SAW device.（iii） The Hall Effect measurements show that the samples have high resistivity, which can meet the requirements of SAW devices.III Properties of ZnO Films at Various Radio-frequency Power（i） The XRD patterns, PL spectra and EPMA demonstrate that the sample at the radio-frequency Power of 70W has the best crystalline quality, the strongest PL intensity and the highest Zn/O atomic ratio, which can possibly help improve the understanding of obtaining high quality ZnO deposited on FTDF.。（ii） The SEM morphology shows that the sample at the radio-frequency Power of 70W is of a relatively clean surface, which is expected to give a high coupling factor for SAW devices.（iii） Hall Effect measurement shows high resistivity of all the samples, which can meet the requirements of SAW devices.更多还原