氮掺杂p型ZnO薄膜的生长及理论研究

【作者】 臧剑栋；

【导师】 李燕； 邓宏；

【作者基本信息】 电子科技大学 ， 电子信息材料与元器件， 2008， 硕士

【摘要】 ZnO是一种宽带隙半导体材料（Eg=3．37eV），因其非常优越的光电性能及其在光电子器件中的巨大应用价值而被誉为“二十一世纪半导体”。通常在制备ZnO材料的过程中会产生氧空位和锌填隙原子，这些缺陷使ZnO呈n型导电特性，所以n型掺杂容易实现。同时，氧化锌中存在的本征施主缺陷，对受主掺杂产生高度自补偿作用，并且受主杂质固溶度很低，这导致生长p型ZnO及制备p-n结非常困难。p型ZnO的制备已成为ZnO作为半导体光电子材料的发展瓶颈，也是当今半导体光电子领域研究的世界性难点和热点之一。V族元素被认为最有望获得ZnO的p型掺杂。N在V族元素中离子半径和p轨道能量都是最小的，而且N的离子半径跟氧接近，因此N被认为是实现p-ZnO最合适的受主元素之一。目前制备ZnO：N薄膜主要有MBE、MOCVD、溅射、PLD和Zn₃N₂热氧化法，但存在着工艺复杂，设备昂贵和源有毒等问题。因此通过SSCVD工艺，使用自行设计合成的新型固态源Zn₄（OH）₂（O₂CCH₃）₆·2H₂O生长出p型ZnO薄膜具有非常重要的现实意义。本文在系统阐述了ZnO的性能与应用及其制备技术、缺陷与掺杂方式等基础上，对ZnO的p型掺杂进行了研究，通过多种测试手段和理论分析，取得了一些阶段性成果：1、用本试验室自行设计的SSCVD装置，利用两步法工艺，通过氮的掺杂，实现了ZnO的p型转变，薄膜具有较好的a-b轴取向和可见光区约为70-80％的透过率。2、具体研究了衬底温度对ZnO薄膜p型掺杂的影响。基片温度为500-600℃时获得了p型ZnO薄膜，而且在600℃时，空穴浓度为3．12×10¹⁶cm^-3、电阻率为1．34Ωcm、迁移率为149．01 cm²／Vs。3、SSCVD一步法无法实现氮的掺入，薄膜呈现富锌状态，并且PL谱中存在激子-激子相互碰撞引起的受激辐射峰。4、采用SSCVD两步法工艺，在Si（100）衬底上形成p-ZnO／n-Si异质结二极管，其Ⅰ-Ⅴ曲线显示了整流特性。5、利用第一性原理计算了ZnO：N_O+V_Zn模型的电子结构，通过比较理想配比ZnO、ZnO：N和ZnO：N_O+V_Zn模型电子结构的不同，可知：V_Zn展宽N产生的深能级缺陷态，减弱了受主能级局域化程度，从而激活了N原子，提高了N原子的固溶度，使N原子能更容易的掺入ZnO中，从而可以制备高质量的稳定p型ZnO薄膜。更多还原

【Abstract】 Zinc Oxide （ZnO） is an important wide band gap semiconductor materials （Eg=3.37eV）, which is known as twenty-first century semiconductor due to its excellent optoelectronic performance. Nominally undoped ZnO typically exhibits n-type conductivity ascribed to native point defects such as oxygen vacancies （V_O） and zinc interstitials （Zn_i）. The fabrication of p-type ZnO is difficult due to the self-compensation effect from native defects and low solubility of p-type dopants. The fabrication of p-type ZnO has become the bottleneck of the application of ZnO-based optoelectronic devices. In recent years, ZnO films have attracted a considerable amount of interest in the world.Group-V dopants have been considered as possible dopants for p-type ZnO. Among these acceptors, N has proven to be suitable acceptor for making p-type ZnO, since the ionic radius of N is about of O. N-doped ZnO （ZnO:N） films have been fabricated by various deposition methods such as molecular-beam epitaxy, metalorganic chemical vapor deposition, sputtering, pulse laser deposition, and thermal oxidation of Zn₃N₂, but the methods exist these problems such as complex process, expensive equipment and poisonous solid precursor. Therefore, it is very important to realize p-type ZnO by single source chemical vapor deposition （SSCVD） using a novel solid precursor of Zn₄（OH）₂（O₂CCH₃）₆·2H₂O.In this thesis, based on a comprehensive review of the theories and fabricating techniques of ZnO materials and p-type doping, we conducted a detailed study of ZnO p-type doping. The main content of this thesis is as follows:1. Nitrogen-doped p-type ZnO thin films have been realized by two-step SSCVD. Thin films exhibit a-b preferential orientation and transparency of about 70-80% in the visible-light region.2. The effect of substrate temperatures on the conductivity of ZnO:N by two-step SSCVD. It is shown that ZnO:N films become p-type material at substrate temperatures between 500-600℃. An optimized result with a resistivity of 1.34Ωcm, Hall mobility of 149.01 cm²/Vs, and hole concentration of 3.12×10¹⁶cm^-3 was achieved at 600℃. 3. The one-step SSCVD method can’t realize ZnO:N, and ZnO by one-step SSCVD contain excessive Zn atomic. Photoluminescence spectra show the stimulated emission peak due to exciton-exciton scattering.4. p-ZnO/n-Si heterojunction was fabricated by deposition of a N-doped p-type ZnO layer on a n-type Si（100） layer. The I-V characteristics of the p-n heterojunction show a rectifying behavior.5. Electronic structures of ZnO:N_O+V_Zn was calculated by the first-principle. Comparing with the electronic structures of ZnO, ZnO:N, ZnO:N_O+V_Zn, it was revealed that V_Zn broadened the acceptor level produced by doping N, weakened localized of donor level, activated N atom and increased the solubility of N. The results indicate that high quality p-type ZnO thin films can be fabricated by doping N into ZnO:V_Zn.更多还原