【作者】 程轶；

【导师】 杜国同；

【作者基本信息】 大连理工大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 β-Ga2O3是一种直接、宽带隙半导体材料,带隙宽度在4.2-4.9eV之间。β-Ga2O3具有很好的光学和电学特性,在近紫外、可见光和近红外区域透过率很高。室温单晶β-Ga2O3由于氧缺陷、镓缺陷的存在呈现n型导电特性。其他元素,如Si、Sn掺入可以提高β-Ga2O3的导电特性。Dy、Eu和N元素掺入可以改变Ga203材料的光学特性。因为β-Ga2O3薄膜在紫外区具有较高的光电导特性,β-Ga2O3材料被认为是一种新颖的、有发展前景的深紫外日盲探测器材料。目前许多薄膜沉积和生长技术被用来制备β-Ga2O3薄膜材料,如金属有机物化学气相沉积(Metal organic chemical vapor deposition, MOCVD)、分子束外延(Molecular beam epitaxy, MBE)、脉冲激光沉积(Pulsed laser deposition, PLD)、溅射等,而热蒸发技术是传统、成熟、沉积速率快、易于工业生产的一种常用的制备薄膜技术,目前关于电子束蒸发技术制备β-Ga2O3薄膜材料鲜少有报道。多晶半导体材料由于结构特殊,相对于单晶材料比较容易制备,而且具有很多优越的性质,现在已经成为半导体材料研究的热点问题之一。本文主要利用电子束蒸发技术分别在蓝宝石和硅衬底上制备了β-Ga2O3薄膜和Cu掺杂的β-Ga2O3薄膜。具体研究内容如下：采用电子束蒸发技术,在蓝宝石衬底上制备了高透过率的β-Ga2O3薄膜。然后将β-Ga2O3薄膜在1000℃温度下、氧气和氮气氛围中进行退火处理,比较退火氛围对β-Ga2O3薄膜晶体结构、表面形貌和光学特性影响。实验结果发现,氧气氛围退火更有利于提高β-Ga2O3薄膜晶体质量。在氧气中退火后,β-Ga2O3薄膜光致发光谱探测到了330nm紫外波段发光和706nm近红外波段发光。β-Ga2O3多晶薄膜光学禁带宽度5.1和5.7eV,与单晶的体材料β-Ga2O3有很大区别,根据薄膜的X射线衍射谱(X-ray diffraction, XRD)、表面形貌和透射电镜选区电子衍射谱证实薄膜是多晶结构,β-Ga2O3薄膜中包裹着不同尺寸的晶粒,在量子尺寸效应的作用下,β-Ga2O3的光学带隙增大。红外光谱探测到了特征吸收峰位于460cm-1波数Ga-O伸缩振动吸收峰,670cm-1波数的与β-Ga2O3材料相关的吸收峰,以及760cm-1波数的Ga-OH伸缩振动吸收峰。此外发现新的吸收峰,位于560cm-1波数位置,推测是与β-Ga2O3材料相关的伸缩振动吸收峰。基于蓝宝石衬底的GaN半导体二极管(Light emitting diodes, LED)由于衬底的热导性、电导性差,而限制了高功率的LED器件制备。采用衬底剥离技术,实现衬底转移可以提高器件功率,同时提高蓝宝石衬底应用,降低器件制作成本。β-Ga2O3与蓝宝石衬底和GaN材料都有较小的晶格失配,是非常好GaN材料LED器件牺牲层材料。因为采用MOCVD技术外延生长GaN一般需要1000℃左右的生长成核温度,β-Ga2O3材料在1000℃温度结构稳定性是需要研究的重点内容,它直接影响着GaN基LED器件质量。因而论文首次研究1000℃氧气的氛围中,Ga203结构和光学性质随着退火时间的变化关系。实验结果说明退火后β-Ga2O3薄膜是多晶结构。退火后样品的晶体质量相对于未退火样品都提高了,XRD衍射峰强度增加同时半高宽减小,退火时间30、60和90分钟的时候,衍射峰强度变化不大,但是当时间到120分钟的时候,衍射峰强度明显减弱,说明薄膜晶体质量开始变坏。同样的现象在表面形貌和发光谱中都观测到了,因而实验说明在30-90分钟内,β-Ga2O3薄膜性质稳定,时间到达120分钟后薄膜性质变差。原创性地采用电子束蒸发物理方法在蓝宝石衬底上制备了Cu掺杂β-Ga2O3薄膜,研究了Cu元素掺杂对β-Ga2O3薄膜的结构特性和光学特性的影响,光致发光光谱测试结果发现Cu元素掺杂使薄膜的黄绿发光峰位置红移到520nm波长,XRD衍射峰的位置也发生了偏移,因为Cu离子半径大于Ga离子半径,因而Cu取代Ga位,使晶格发生了微小变化。X射线光电子能谱发现了二价铜离子和一价铜离子的存在。然后系统的研究了退火温度、衬底生长温度和生长速率等因素对Cu掺杂β-Ga2O3薄膜的结构特性和光学特性影响。实验结果说明衬底400℃、退火温度1000℃有利于制备高质量的Cu掺杂β-Ga2O3薄膜,该实验参数对研究Cu掺杂β-Ga2O3薄膜提供了有意义的参考。初步探索了在硅衬底上沉积制备β-Ga2O3薄膜和Cu掺杂β-Ga2O3薄膜特性,研究了硅衬底上生长β-Ga2O3薄膜和Cu掺杂β-Ga2O3薄膜XRD特性、红外光谱(Fourier transforming infrared, FTIR)特性和发光特性。更多还原

【Abstract】 β-Ga2O3is regarded as a promising candidate material for optoelectronic devices because of its wide direct bandgap of4.2-4.9eV.β-Ga2O3has stable structure properties and stable optoelectronic properties, meanwhile, the transmissivity of β-Ga2O3is high in near ultraviolet, visible light and near infrared light region. At room temperature, crystal β-Ga2O3exhibits n type conducting properties due to the gallium vacancies and oxide vacancies. Doping with other element, such as Si、Sn and so on, would improved the conducting properties of β-Ga2O3material. As reported, doping with Dy, Eu and N element, would change the optical properties of β-Ga2O3. β-Ga2O3is regarded as the novel and promising candidate for ultraviolet photodectors. The β-Ga2O3films have been prepared by several methods, such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and sputtering. However, there are few reports on the thermal evaporation technique. As is well known, the thermal evaporation technique is traditional and convenient method to fabricate film. Herein, it is flexibly and widely employed in industrial manufacture with the advantage of fast depositing rate. Ploy crystalline semiconductor material has unique properties comparing with crystalline material. It is easy to prepared polycrystalline β-Ga2O3. It is focusing much attention on the polycrystalline β-Ga2O3because of some excellent properties. In this paper, using electron beam evaporation method, we prepared β-Ga2O3and Cu doped β-Ga2O3film on sapphire and silicon substrate, respectively. The detailed work is shown as following.Using electron beam evaporation method, β-Ga2O3was deposited on c-plane Al2O3substrates. As-grown β-Ga2O3samples were subsequently annealed at1000℃under nitrogen or oxygen for1hour. And the micorstructure, surface morphology and optical properties were investigated. It was indicated that the annealing treatment in oxygen atmosphere was more effective to improve the crystalline properties of β-Ga2O3than in the nitrogen atmosphere. The photoluminescence (PL) showed broad ultraviolet emission centered at330nm and broad red emission centered at706nm. The optical bandgap of β-Ga2O3was deduced to be5.1and5.7eV, which was distinctly different with that’s of the bulk crystal. Based on the X-ray diffraction (XRD), surface morphology and selected area transmission electron microscope images, It was suggested the quantum size effect caused the broadening of the optical bandgap. Fourier transforming infrared (FTIR) transmittance spectra was recorded in the range of3600-400cm-1. The IR band at460cm-1was assigned to Ga-O vibrations, and the band at670cm-1was relative with the β-Ga2O3. The band at760cm-1was assigned to Ga-OH vibrations. In addition, the new band at560cm-1was deduced to be arising from the β-Ga2O3.Particularly for special application, the β-Ga2O3was evaluated to be the excellent sacrificial substances in the GaN/Ga2O3/sapphire structure. As is well known, the thermal conductivity of sapphire is not high enough for large scale GaN based light emitting diodes (LED). One of effective ways of enhancing the performance of optoelectronic devices is the transfer of prefabricated devices from conventional sapphire substrates onto more thermally and electrically conductive substrates. Due to the2.6%of the minimum lattice mismatch between β-Ga2O3and GaN, the successful growth of GaN on Ga2O3buffer layers has been reported to act as the sacrificial materials for chemical lift off process. Generally, epitaxial growth of GaN on sapphire with MOCVD method required high temperature around1000℃. Both sacrificial buffer layers and various optoelectronic devices based on Ga2O3material required stable and reliable structural and physical properties, especially in the conditions of active oxygen ambient at high temperature. β-Ga2O3films with polycrystalline structure were prepared on c-plane sapphire substrate. XRD patterns indicated that the grain orientations were promoted and the grain sizes enlarged with annealing time increasing. Considered the XRD patterns, the Ga2O3films annealed for30,60and90minutes showed similar structure properties. The PL spectra exhibited violet, green and red emissions, which were affected by the annealing time. Therefore, it was concluded that the β-Ga2O3films would remain stable structure and optical characteristics when they were annealed for30to90minutes. However, if the annealing treatment time arrived to120minutes, the crystalline properties of β-Ga2O3film became worse.Cu doped β-Ga2O3thin films were deposited by electron beam method with subsequent annealing at1000℃for1hour. The influence of the Cu dopant on the crystal structure, surface morphologies and optical properties of β-Ga2O3films was investigated. XRD patterns indicated that the optimum orientations of the films were promoted by high temperature annealing treatment. The PL spectra of the annealed samples presented violet and green emissions, and the peak of green emissions red shift to520nm wavelength. The X-ray photoelectron spectroscopy (XPS) result indicated that the Cu ions were effectively doped into the β-Ga2O3films with univalent and bivalent chemical states. Then, we researched the effects of the deposit parameters on the Cu doped β-Ga2O3thin films properties, such as annealing temperature, substrate growth temperature and depositing speed. In summaries, we obtained the optimized deposit parameter of Cu doped β-Ga2O3films, which was400℃of substrate temperature and1000℃of annealing temperature. It would be useful to future research on the properties of Cu doped β-Ga2O3films.Lastly, we prepared the β-Ga2O3film and Cu doped β-Ga2O3films on silicion substrate. The influence of the silicon substrate on the crystal structure and optical properties of β-Ga2O3films was investigated by X-ray diffraction, photoluminescence spectra and FTIR transmittance spectra.更多还原