【作者】 兰伟；

【导师】 王印月； 严辉；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2007， 博士

【摘要】 基于价带化学修饰（CMVB）理论首先被发现的Cu⁺基p型透明导电氧化物CuAlO₂薄膜具有独特的光电特性，它的成功开发为实现半导体全透明光电器件如透明二极管、透明晶体管提供了可能性，也推动了传统意义上透明导电氧化物（TCO）薄膜到透明氧化物半导体（TOS）薄膜的发展。然而，制备性能良好的CuAlO₂薄膜一直是一个难题，到目前为止已经有许多方法被用来制备该薄膜，但是所制备的薄膜结构与性能差异很大。针对目前国内外在CuAlO₂薄膜方面的研究现状，结合溅射法所具有的众多优点特别是在工业化大规模生产中所具有的优势地位，我们探索使用射频磁控溅射法在石英和Si衬底上制备高质量p型CuAlO₂薄膜，已经取得了一定的工作进展，归纳起来可以概括为以下几部分。1．通过对溅射参数的调节成功抑制了Cu⁺的氧化，在石英和Si衬底上沉积了以CuAlO₂相为主、兼有少量Cu₂O相的Cu-Al-O薄膜。厚度为300nm左右的薄膜对可见光的透过率介于60％～70％之间，计算拟合得到直接和间接带隙分别为3.52eV和1.83eV左右。Cu-Al-O薄膜的最低室温电阻率为2.2×10²Ωcm，在近室温区Cu-Al-O薄膜电导率随温度变化遵从Arrhenius规律，揭示了薄膜导电符合半导体热激活机制。2．利用CuAlO₂强烈的各向异性电导率(σ_ab>>σ_c)特性，对CuAlO₂薄膜样品进行退火处理（氮气气氛保护900℃退火5h）成功获得了沿（001）晶面优先取向生长薄膜，实现了电阻率三个数量级的降低。退火CuAlO₂薄膜对可见光透过率在60％附近，红外光高于80％，拟合发现CuAlO₂薄膜具有四个不同能量范围的直接带隙，分别是～3.00eV、～3.15eV、～3.50eV和～3.75eV，可能对应布里渊区不同点的直接跃迁。研究发现金属Ag电极与退火CuAlO₂薄膜之间具有良好的欧姆接触，最小接触电阻率为0.32Ωcm²。该p型薄膜具有最小电阻率37Ωcm，比未退火薄膜下降了3个数量级。优先取向生长CuAlO₂薄膜在近室温区（＞190K）符合热激活导电机制，低温区（＜185K）以二维变程跳跃导电模型为主。3．鉴于富余氧原子在CuAlO₂薄膜导电特性方面所起到的重要作用，不同氧分压CuAlO₂薄膜被制备，发现富余氧原子在提供有利于薄膜p型导电环境的同时，对CuAlO₂薄膜的结构也造成了一定程度的影响。通过使用XRD、Raman和AFM等手段详细研究了不同氧分压CuAlO₂薄膜在经退火处理之后的结构和微结构变化。发现20％氧分压CuAlO₂薄膜表现出了最佳的结构特性。由于富氧原子处入CuAlO₂晶格间隙位加剧了沿c轴方向负热膨胀行为而造成较大的内应力，薄膜在释放内应力的同时导致薄膜表面出现一些微观空洞，而且随着氧分压的增加微观空洞逐渐增多变大变深，最终在60％氧分压时致使薄膜成为非晶态。4．实现了n型低阻Si衬底上制备p型CuAlO₂薄膜而构成的突变异质结。在Ag/Si/Ag和Ag/CuAlO₂/Ag测量Ⅰ-Ⅴ特性均显示线形变化的基础上，检测发现p-CuAlO₂/n-Si异质结具有较好的整流特性，开启电压为0.5V左右。由于Si的载流子浓度高出CuAlO₂ 3～4个数量级，按照p-n⁺单边突变结理论对该异质结进行了计算拟合，发现界面态效应和串联电阻效应是影响该异质结整流特性的重要因素，并且拟合得到串联电阻为13Ω。5．鉴于N元素在p型TCO薄膜中所起到的受主杂质作用，采用半导体掺杂技术成功实现了对CuAlO₂薄膜的受主N掺杂。以N₂O气体为N源，按不同流量比混入溅射气体中制备N掺杂CuAlO₂薄膜。AES检测发现CuAlO₂薄膜中Cu、Al原子比符合化学计量比，当N₂O流量比为15％时，薄膜中的N原子含量基本饱和，达到CuAlO₂化学计量比中O原子的5.9at.％左右。N掺杂CuAlO₂薄膜的最小电阻率为10Ωcm，最大载流子浓度为10¹⁶cm^-3，与未掺杂薄膜相比分别降低和提高了一个数量级。掺杂CuAlO₂薄膜光学透明度基本上未发生变化，在可见光范围内透过率介于60-70％之间，对近红外光透过率最高超过85％，而掺杂样品的光学吸收边与未掺杂相比出现了蓝移，可能与掺杂产生空穴载流子造成的Burstein-Moss效应有关。更多还原

【Abstract】 Based upon the theory of "the chemical modulation of the valence band", was firstly discovered as a p-type transparent conducting oxide （TCO）, which has the especial optical and electrical properties. The discovery of p-type TCO made possible the fabrication of transparent oxide optoelectronic devices such as transparent p-n junction diodes and transistors using an appropriate combination of p-and n-type TCO films, which also led TCO material to the frontier of transparent oxide semiconductor （TOS）. However, the preparation of CuAlO₂ film with excellent properties always is a very difficult case. Up to now, several techniques, such as pulse laser deposition, plasma enhanced chemical vapor deposition and sputtering, have been used to synthesize CuAlO₂ films, which are very different on the structure and optical/electrical properties. Considering issues about the present developing state of CuAlO₂ film and the superiority of sputtering in the industrialization, the dissertation is aimed at fabricating high-quality p-type CuAlO₂ films on quartz glass and Si substrates using rf magnetron sputtering, the main research processes achieved have been summed up as following:1. The optimized parameters have been obtained successfully to deposit Cu-Al-O films on quartz glass and Si substrates. The determination of chemical composition and valence has been solved. CuAlO₂ phase is found the dominator in Cu-Al-O films and a little Cu₂O also exists. The transmittance of Cu-Al-0 film with the thickness around 300 nm is about 60⁷0 % in the visible light range. The direct and indirect band gaps of the films are estimated by the linear fitting around 3.52 and 1.83 eV, respectively. The minimal resistivity of Cu-Al-0 film is 2.2×10²Ωcm at room temperature. Temperature dependence of the conductivity is in accord with the Arrhenius rule, indicating that the film is of semiconducting thermal-activation type in the near room temperature range.2. Actively utilized the anisotropic conductivity property (σ_ab>>σ_c) of CuAlO₂, the decrease of the resisitivity around three orders of magnitude for CuAlO₂ film is realized by the optimized annealing technique （in N₂ ambient at 900℃for 5 h）. For the annealed CuAlO₂ film, the transmittance is around 60 % in the visible light range and above 80 % in the near infrared light. It is found that there are four direct band gaps around -3.00, -3.15, -3.50 and -3.75eV, respectively, estimated from the transmittance and reflectance data of the annealed films. They might be related with the different direct transitions in the Brillouin zone. The excellent ohmic contact is obtained between Ag electrodes and the annealed films, and the specific contact resistance can be decreased to 0.32Ωcm-2. The minimal resistivity of the annealed CuAlO₂ film is 37Ωcm, which is lower three orders of magnitude than that of the as-deposited one. Temperature dependence of conductivity for p-type CuAlO₂ film can be described by a thermal-activation theory when the temperature is above 190 K, but below 185 K a two-dimension variable-range hopping mechanism becomes dominant.3. For the native p-type CuAlO₂ film, adequate rich-oxygen is in favor of the improvement of the conductivity. However, the effect of the rich oxygen atoms on the structural properties for annealed CuAlO₂ film is also very obvious. The annealed films deposited at different oxygen parital pressures were characterized by XRD, Raman and AFM. It is found that the film prepared at 20 % oxygen partial pressure exhibits the excellent structure property. When the oxygen partial pressure is above 20 %, the anisotropic expansion behavior of CuAlO₂ will be obviously aggravated due to the excess oxygen atoms in interstitial position, which results in some microscopic cavities appeared in the surface of the films to release the internal stress during the annealing treatment. Moreover, the cavities become large with increasing oxygen concentration, which gradually degenerate the CuAlO₂ film to the amorphous state up to 60 % oxygen partial pressure.4. The p-CuAlO₂/n-Si heterojunction has been firstly prepared through sputtering CuAlO₂ film on low resistance Si substrate. Based upon the linear I-V characterizations of Ag/Si/Ag and Ag/CuAlO₂/Ag, the p-CuAlO₂/n-Si junction is detected a good rectifying property with the cut-in voltage of 0.5 V. Because the carrier concentration of n-Si is larger 3-4 orders of magnitude than that of p-CuAlO₂, the heterojunction can be fitted by the theory of p-n⁺ one-sided step junction. It is found that the effect of the interface state and series resistance is not neglected for the rectifying property of the junction. Moreover, the series resistance is fitted around 13Ωfor p-CuAlO₂/n-Si heterojunction.5. N doped CuA102 films have been prepared successfully by sputtering under the mix ambience of N₂O, O₂ and Ar. N concentration detected by AES is 5.9 at.% for the film doped with 15 % N₂O specific flux, indicating that acceptor impurities N are doped into CuAlO₂ films indeed. The optimal N doped film shows the minimal resistivity of 10Ωcm and the maximal hole concentration of 10¹⁶cm^-3, which are decreased and increased one order of magnitude comparing with the undoped CuAlO₂ thin film, respectively. The transmittance of N doped CuAlO₂ films are 60-70 % in the visible light range and above 85 % in the near infrared light. A blue-shift of optical absorption edge is observed for N doped CuAlO₂ film, which might be due to the Burstein-Moss effect.更多还原