【作者】 马艳；

【导师】 杜国同；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2004， 博士

【摘要】 宽直接带隙Ⅱ-Ⅵ族化合物半导体材料ZnO，由于其光电特性受缺陷影响较小，激子束缚能较高（60meV，GaN为25meV），体材料可得，生长温度较低（可在200-700℃左右成膜，比GaN低几百度），并且材料来源广泛、价格低廉，而成为继GaN之后在光电研究领域，极有希望用于紫外和蓝色发光器件的新型光电子材料。利用ZnO材料，可以制作紫外探测器、紫外发光管和激光器、高频表面声波器件、透明导电电极、微型传感器等，其在航天、通讯、卫生等高新技术领域和广阔民用领域都具有广泛的用途。制备ZnO薄膜的方法有很多，包括：溅射方法（sputtering）、金属有机气相外延（MOVPE）、分子束外延（MBE）、脉冲激光沉积（PLD）、原子层外延（ALE）、等离子体加强化学气相沉积（PECVD）、溶胶-凝胶法（soll-gel）、喷涂热解法（spray pyrolysis）、电子束蒸发法（e-beam evaporation）等等。从目前生长高质量ZnO薄膜、研究p型掺杂、制作ZnO发光二极管及ZnO材料的能带工程等方面来看，人们更多的还是把注意力集中在MOVPE、MBE、PLD以及溅射方法上。本论文即利用MOVPE方法，在不同的衬底Al₂O₃、CaF₂、GaAs上生长ZnO薄膜，采用独特的X射线衍射技术，首次深入分析了ZnO薄膜的生长取向偏差，并研究了外延生长过程中，生长温度和氧源流量对ZnO薄膜性质的影响，同时对ZnO薄膜的N掺杂以及p型ZnO薄膜的制备进行了研究。 实验中发现：在Al₂O₃衬底上生长的ZnO薄膜，其在外延生长过程中明显存在与c轴及与生长平面的取向偏差，偏离程度与生长温度密切相关，在550℃下生长的薄膜结晶质量较好，其柱状晶粒与c轴方向的偏差为2.7°，扭转相中a轴与生长平面的偏差为2.5°；在620℃下生长的薄膜结晶质量较差，其柱状晶粒与c轴方向的偏差为6.3°，扭转相中a轴与生长平面的偏差为14°，这主要是由于生长温度的升高加重了两种源的气相预反应，生成的ZnO粉末颗粒影响到衬底上薄膜的成核和进一步生长的缘故。以蓝宝石Al₂O₃（001）为衬底生长ZnO薄膜，二者的外延对应关系为：ZnO（001）//Al₂O₃（001），ZnO[100]//Al₂O₃[110]，ZnO[100]//Al₂O₃[100]。同时发现，生长温度对ZnO薄膜的结构、形貌以及光电特性都有着显著的影响。600℃生长的薄膜，各晶吉林大学博士学位论文产碑 急柱尺寸最小，薄膜表面起伏较大，而550℃生长的薄膜，晶柱不很明显，晶柱间相互融合，薄膜表面起伏较小。但在600℃下生长的薄膜发光质量较好，其光致发光谱中几乎看不到深能级发光峰，紫外峰与深能级发光峰强度比值可达167:1。 我们还发现:氧气流量的大小也明显影响薄膜的结构、表面形貌及其光电特性。在当前生长条件下，增加氧气流量，Zno薄膜的结晶质量有所下降，由单一c轴取向变为多取向薄膜，并且柱状晶粒尺寸减小，但薄膜表面更加光滑平整。ZnO的光致发光特性同薄膜中的Zn、O组份配比密切相关，随着氧气流量的增加，光致发光谱中紫外峰明显增强，而深能级峰明显减弱，二者峰强比值达到148:1，薄膜的光学质量有所提高。氧气流量的增加，同时也使薄膜的电阻率升高，载流子浓度和迁移率随之下降，Zno薄膜中的n型导电也许来自于氧空位V。。 对ZnO薄膜的掺杂研究表明:NH3经射频源离化后，可以将N元素有效地掺入到ZnO薄膜当中形成高阻薄膜，当NH3气流量为90sccm/min时，Zno:N薄膜结晶质量较好，但为多种取向膜;XPS分析表明，掺入的N元素形成Zn一N键，N原子替代0原子的位置而成为受主。 在CaFZ（1 11）衬底上，在国内，我们首次生长了较高质量的Zno薄膜，薄膜为c轴择优取向，（002）面X射线衍射峰半峰宽只有0.18“，薄膜高度透明，透过率超过90%，并且表面光滑平整，均方根粗糙度为6.744nm。 10K温度下的PL谱中，可以明显观察到A、B自由激子的辐射复合发光峰，它们分别位于3.374ev和3.385ev。PL谱中的主峰来自于施主束缚激子的辐射复合（D0x），其位于3.362ev。另外，我们还可以观察到受主束缚激子的发光峰（Aox）、施主一受主对（DAP）的发光峰及自由激子、施主束缚激子（Dox）的声子伴线。Zno薄膜显示n型电导，电阻率为114Ocm，载流子迁移率为15.7cmZ/Vs，载流子浓度为3.50 X 10’sem一，。 在GaAS（001）衬底上，当生长温度为6 1 ooC，02流量为1 30Seem/min时，生长的薄膜柱状晶粒尺寸较大，结晶较好，（002）衍射峰半高宽Fw阴为0.185。。分析结果表明:生长过程中02流量的大小明显影响Zno/G aAs薄膜的光致发光特性。02流量增加，会使紫外峰显著增强，深能级发光峰明显减弱，深能级发光峰同氧空位密切相关。生长的ZnO/GaAS薄膜，在仇流量为180sccm/min:、/o/吉林大学博士学位论文产. - 白.时，薄膜电子迁移率最高，为30.4。mZ/Vs，电阻率也最高，为647 Qcm，相应载流子浓度最低，为1.ZX10‘4cm一，。 我们首次采用MOVPE技术，利用过量的氧消除Zno中的自补偿效应的方法，成功制备了本征p一ZnO薄膜。实验中发现，氧气流量的大小是一个至关重要的工艺参数。在当前生长条件下，当氧气流量高于1705。cm/min，得到的为p一Zno薄膜。其最大载流子迁移率可达9.23cmZv一，s一，，相应的载流子浓度为1.59x1016cm一，更多还原

【Abstract】 ZnO, as a promising wide band-gap semiconductor (Eg=3.37eV), attracts as much attention as GaN for its potential utilization in short-wavelength light-emitting/detecting devices. In comparison to GaN, its optoelectronic characteristics are little affected by the defects, and it has higher exciton binding energy (60meV at room temperature), lower growth temperature and cost. ZnO materials can be used in many fields, such as display devices, sensors, piezoelectric transducers, transparent conductor, surface acoustic wave devices and lasers operating in the near ultraviolet and blue spectral range. ZnO thin films can be deposited by various methods, such as sputtering, e-beam evaporation, spray pyrolysis, sol-gel, pulsed laser deposition (PLD), metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), atomic layer epitaxy (ALE), etc. Among these techniques, MOVPE possesses obvious intrinsic advantages, such as selective area growth towards low-dimensional quantum structure, epitaxial lateral overgrowth (ELO) and suitability for growing compound containing volatile elements. It would be especially advantageous for the industrial applications. In this thesis, we prepare ZnO thin films on Al2O3, CaF2 and GaAs substrates by MOVPE and analyze deeply the oriented deviation of growth of the ZnO thin films for the first time. Simultaneously, we investigate thoroughly the influence of the growth temperature and oxygen flow rate on the properties of the films, and the N-doped and intrinsic p-type ZnO thin films are studied systematically.It was found that the growth orientation of the columnar grain in the ZnO films grown on Al2O3 substrates deviated from the c-axis and the growth plane. The deviation was closely related to the substrate temperature. The ZnO films grown at 550癈 had better crystalline quality with smaller orientation deviation, while the films grown at 620 was just on the opposite. The epitaxial relationship between the ZnO films and A12O3 substrate was ZnO (001)//Al2O3(001) , ZnO[100]//Al2O3[110], ZnO[100]//Al2O3[100]. Meanwhile, the growth temperature had quite an effect on the morphology and the opto-electrical properties of the ZnOfilms. The ZnO film grown at 550癈 had larger grain size and smoother surface. But the films with higher optical quality were grown at 600癈 because the deep level emission was barely observed in their photoluminescence (PL) spectra. The intensity ratio of the near-band-edge emission to the deep level emission was as large as 167:1.At the same time, the flow rate of oxygen strongly influenced on the structural and opto-electrical properties of the ZnO thin films on the present growth conditions. Increasing the oxygen flow rate, the crystalline quality of the ZnO thin films was degraded from single-oriented crystal to polycrystalline owning to the formation of O2-induced defects, the averaged grain size became smaller and the root-mean-square roughness decreased. While the optical quality of the films was improved. The intensity ratio of the near-band-edge emission to the deep level emission reached to 148:1 in PL measurements. Thus, the ultraviolet emission in ZnO epilayer might depend strongly on the stoichiometry of the films. Meanwhile, high-O2 content could compensate for the background free-electron concentration generated by native defect of oxygen vacancies, so the electrical resistivity of the ZnO thin films increased with the oxygen flow rate and the electron mobility decreased. The origin of n-type character in un-doped ZnO films was the Vo.NH3-doped ZnO films were grown by plasma-assisted MOVPE. We found that nitrogen could be doped into ZnO films effectively by using plasma generator to realize high-resistivity films. The Zn-N bonds formed in the doped ZnO thin films.High quality ZnO thin film was grown on CaF2 (111) substrate for the first time in china. The film exhibited the preferential (002) orientation with c-axis perpendicular to the surface of the substrate. The full-width at half-maximum (FWHM) of (002) peak in XRD was as narrow as 0.18. At the sam更多还原