【作者】 苏剑峰；

【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】 作为第三代宽禁带半导体材料,SiC和ZnO由于其自身优异的性能一直是人们研究的热点。SiC具有高的迁移率、优异的热稳定性和化学稳定性,在高频、大功率、耐高温、抗辐射等电子器件方面有着巨大的应用潜力。然而,SiC单晶价格昂贵,这就促使人们继续探讨在Si衬底上异质外延SiC薄膜。ZnO的激子结合能高达60meV,被认为是有望取代GaN的新一代短波长光电子材料。但是高质量的p型ZnO制备的困难阻碍了ZnO基激光二极管、发光二极管的实用化进程。另一方面寻找其它p型材料来异质外延n型ZnO薄膜以期能够实现异质pn结的电致发光的方法也引起人们的广泛关注。围绕上述背景,本论文主要开展了以下工作:1)Si衬底上SiC薄膜的异质外延生长一直是人们关注的焦点。“两步法”是在Si衬底上异质外延SiC薄膜的基本工艺,但在高温碳化过程中硅衬底中的硅原子向外扩散容易导致界面空洞的产生,这对后期器件制备很不利,在此基础上我们提出了“三步法”外延SiC薄膜,即碳化—小流量缓冲层—生长。在碳化过程中引入硅烷可以有效地抑制衬底中硅原子的外扩散,避免界面空洞的产生,并提高SiC薄膜的结晶质量。这一改进,可大大改善基于SiC/Si异质结、ZnO/SiC/Si异质结的器件。2)采用三甲基铝（TMA）做掺杂源,制备p型SiC薄膜。少量TMA的引入可以改善SiC薄膜的结晶质量,增加生长速率,并使薄膜中的应力发生变化,生长模式由三维岛状生长模式转变为二维层状生长模式。由于Si（100）和Si（111）衬底的表面自由能不同,所以受TMA的影响不一样。成功制各了Al∶SiC/n-Si异质结并对该异质结进行电学性质测量和深能级瞬态谱分析,Al受主能级位于价带之上220meV。p型SiC薄膜的研制为以后制备n-ZnO/p-SiC异质结提供了基础。3)研究了Al掺杂ZnO薄膜的电学和光学性质,结合以前N掺杂ZnO薄膜的研究结果采用射频辅助裂解N₂及N-Al共掺杂的方法进行ZnO的p型掺杂研究。通过改变RF功率和TMA流量研究不同N/Al对ZnO薄膜光学和电学性质的影响,并对本征ZnO薄膜和呈现p型性质的ZnO薄膜进行变温的光致发光测量,掺杂与未掺杂的ZnO薄膜中均存在3.312eV附近的发光峰,我们把它归为与N_O有关的受主束缚激子A⁰X。与未掺杂的相比,掺杂薄膜中的A⁰X发光峰向低能方向稍有移动,这与Al的引入对N_O受主能级的影响有关。在掺杂薄膜的变温PL谱中,观测到FA的存在,据此估算得受主能级位置为183.7meV。进一步对呈现p型性质的ZnO薄膜进行变激发密度测量,证明了DAP峰位指认的正确性。4)利用二已基锌（DEZ）和H₂O做源在MOCVD系统上初步探索低温下生长高质量的ZnO薄膜。研究发现用H₂O做氧源可大大提高ZnO薄膜的光学性质。通过对载气总流量、源流量比、衬底温度等生长工艺参数进行初步优化后,采用过渡层技术得到了结构和光学性质都比较好ZnO薄膜。通过对退火温度和退火气氛的研究发现,可见发光与V_O、V_Zn、O_Zn有关。AFM表面形貌显示,所得的ZnO薄膜乃三维岛状生长,离我们期望的二维层状生长模式还有距离,所以仍需继续深入研究。更多还原

【Abstract】 As third era wide gap semiconductors,Silicon carbide and Zinc oxide have attracted great attention due to themselves’ excellent properties.Silicon carbide exhibits great potential applications in high frequency、high power、high temperature and high radiation conditions,because it has high electron saturated drift velocity、excellent thermal and chemical stability.While,the SiC single crystal is too expensive, which spur people to keep on study the heteroepitaxial growth of SiC film on silicon substrate.Zinc oxide has a high excition binding energy of 60meV at room temperature,and it is considered to be a new photo-electric material in shortwave length as GaN.However,the applications of higher-efficiency laser diode and light emission diode devices have been limited by the lack of reliable p-type ZnO.On the other hand,to realize the EL on the bases of ZnO,hunting for other wide bind gap p-type materials and hetero-epitaxy ZnO films on them has attracted people’s attentions.Based on the research background,the major works and conclusion are listed as follows:Firstly,there has been a great deal of interest in heteroepitaxial growth of SiC films on silicon substrates."Two steps method" is the basic technics for the hetero-epitaxy growth of SiC films on silicon substrates.However,the interface holes which were induced by the diffuse of Si atom from silicon substrates during the high temperature carbonization processes will cause serious damage to electronic devices.Under this conditions,"Three steps method" was promoted which is consist of carbonization, little flux buffer layer and SiC film growth for the hetero-epitaxy growth of SiC films. The introducing of Silane during carbonization could restrain the out-diffusition of Si atom and reduce the interface holes effectively,and then increase the crystal quality of SiC films.This improvement will facilitate the development of devices which based on the hetero-junction of SiC/Si and ZnO/SiC/Si.Secondly,during the growth of p-type SiC films,it is found that the introducing of TMA could improve the crystal quality of SiC films and increase the growth rate, which will lead to the relaxation of strain stress in SiC films.Moreover,the growth process varies from three-dimensional island-growth mode to step-flow growth mode after introducing TMA during SiC films growth.The influence of TMA on the growth of SiC films on the Si（100）and Si（111）substrates varied,this is because the surface free energy of Si（100）and Si（111）is different.The Al:SiC/n-Si hetero-junction was fabricated successfully,and then its electrical properties and deep level transient spectroscopy were analysised.According to deep level transient spectroscopy,The acceptor energy level was calculated which is 220meV.Based on p-type SiC films,the n-ZnO/p-SiC could be prepared and its EL properties could be investigated in the following work.Thirdly,the electrical and optical properties of Al-doped ZnO films have been studied.Based on the results of N-doped ZnO film by the plasma-assisted metal-organic chemical vapor deposition,p-type ZnO films were prepared by N-Al codoping.The change of optical and electrical properties of ZnO films were studied by varied the RF power and the flux of TMA.To investigate the luminescence mechanism of N-Al doped ZnO films,low temperature photoluminescence spectra was measured.The peak near 3.312meV was existed both in undoped and N-Al doped ZnO films.We classified this peak as the transition of the acceptor-bound excition （A⁰X）related to No acceptor.Compared with the position of A⁰X in undoped ZnO films,the peak of A⁰X shifted to lower energies,and this phenomenon was induced by the incorporation of Al.A photoluminescence recombination possibly due to the free-electron-to-acceptor（FA）transition was observed at temperatures higher than 40K in N-Al doped ZnO films.The acceptor ionization energy was estimated from the energy position of the FA luminescence to be 183.7meV.Moreover,the excitation intensity-dependent PL spectra which taken at 80K in N-Al doped ZnO film was measured.The luminescence band labeled DAP shifts to higher energies with increase excitation intensity.Lastly,using DEZ and H₂O as source materials,the growth of high crystal quality ZnO films under lower growth temperature by MOCVD was investigated.Compared with the ZnO films which were grown by using CO₂ as oxygen source material,the ZnO films which were grown by using H₂O as oxygen source material have excellent photoluminescence properties.The total N₂ flow rate、the ratio of Zn/O and the growth temperature were optimized to improve the crystalline quality of ZnO films on silicon substrates.Then by using the buffer layer technique,the ZnO films with high crystal quality and excellent photoluminescence properties were got.The luminescence band in visible range for the annealed ZnO films varied with the annealed temperature and the annealed ambience.The green band is shown to consist of several components,such as V_O,V_Zn,O_Znand so on.The surface morphology shown that the growth of ZnO films proceed three-dimensional island growth mode. So it is still need to take deeper study to realize step-flow growth mode.更多还原