横向外延GaN材料的MOCVD生长与特性研究

【作者】 魏茂林；

【导师】 齐鸣；

【作者基本信息】 中国科学院上海冶金研究所 ， 微电子学与固体电子学， 2001， 硕士

【摘要】 本文围绕GaN材料的金属有机物化学气相淀积（MOCVD）和横向外延过生长（LEO）展开，首先以常规的MOCVD两步生长法为切入点，并在此基础上进行了GaN材料的LEO生长研究。获得的主要研究结果包括： 通过对MOCVD反应室气流的理论分析和实验结果，并结合在实际气流中样品的稳定性问题，选择了合适的石墨基座参数。 由于用常规MOCVD法得到的GaN层是下一步LEO生长的基板，所以常规MOCVD生长的GaN材料质量对整个外延过程有着重要的影响。本文在大量实验的基础上，对所用的MOCVD生长工艺进行了优化，包括： 1．确立了合适的外延生长工艺流程； 2．找出了较理想的Al₂O₃衬底表面高温处理条件； 3．选择了合适的GaN缓冲层生长时间； 4．确立了较理想的GaN外延生长温度等条件。 在对常规MOCVD生长GaN材料的工艺进行优化的基础上，本文对用LEO技术生长GaN材料的两个重要方面，即选择生长和横向生长速率进行了实验分析和研究。结果表明： 1．作为LEO生长基板的GaN层，既要具有足够的表面平整度又要能提供 完整的晶体学表面，是实现选择生长的关键。 2．不同的图形方向对横向生长速率与纵向生长速率之比（L/V）有重要影 响，由于不同的图形方向会形成不同的侧面，从而使L/V比的差别很大。 与图形方向沿[1120]相比，当图形沿[1100]方向时，生长更易在侧面进 行，故可获得较高的L/V比。 通过选择合适的工艺条件，本文成功地实现了GaN材料的LEO外延生长。所得样品的X射线衍射半高峰宽，比用常规MOCVD法生长的样品减小了三分之一。更多还原

【Abstract】 GaN has been intensively studied recently due to its superior intrinsic properties such as wide range of direct transition-type energy band gap, high breakdown voltage, and so on. In this thesis, we focused ourselves on the growth and characterization of GaN by metal-organic chemical vapor deposition (MOCVD) and lateral epitaxy overgrowth (LEO). The main achievements obtained in this work are as follows: By analyzing the gas flow in reaction chamber of the MOCVD system and considering the stability of substrate, a proper graphite supporter was selected. Because the GaN layer grown by the conventional two-step process is the base layer for LEO growth, the optimization of the growth condition is very important in the whole process. Based on the experimental results, the growth condition used in this work for GaN by conventional MOCVD was optimized including: 1. Building the proper process; 2. High temperature treating of sapphire substrate surface; 3. Suitable growth time for the buffer layer; 4. Proper growth temperature for the GaN epi-layer. On the basis of optimized MOCVD growth condition, the LEO growth of GaN was studied and much attention was paid on realization of selective area growth and the lateral overgrowth. It was shown that in order to realize the selective area growth, the surface of the GaN layers grown by conventional MOCVD must be smooth enough and with perfect crystallographic plane. It was also found that the lateral growth rate is dependent strongly on the direction of the mask layer. Comparing with the [11 2 0] direction, the [1100] direction results in a relative large ratio of lateral to vertical growth rates (L/V). By using the proper growth process, the GaN samples grown by LEO were successfully obtained in this work. It was found that the X-ray diffraction (XRD) peak width (FWHM) for the LEO samples is 1/3 less than that of the samples grown by conventional MOCVD.更多还原