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Electron microscopy analysis by visualization of relationship between composition distribution and charge distribution in quantum well of GaN system

通过电子显微镜分析 GaN 系统量子阱中成分分布和电荷分布之间的关系

基本信息

批准号：
16560287
负责人：
TAKEGUCHI Masaki
金额：
$ 2.18万
依托单位：
National Institute for Materials Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

Piezo electric field of InGaN layer in InGaN/GaN quantum well structure was measured by electron holography. This piezo electric field was caused by lattice strain along c-axis in InGaN layer. We calculated lattice constant from In composition according to Vegards law, and then estimated piezo-polarization. We prepared some samples with various thickness from one wafer. Electron holography was carried out for those samples and internal electric field value evaluated was 0.7±0.2 MV/cm. This value corresponds to the In composition 4.1±1.3% estimated from the theoretical calculation. On the other hand, Z-contrast STEM observation allowed us to evaluate the In composition 4.8±1.6%, which agree to the value obtained by electron holography.As for AlGaN/GaN quantum well structure, we established the sample preparation technique, e.g., Samples were thinned by wedge-polishing method followed by Ar-ion milling with low voltage, so that the sample thickness was 50-100 nm. This thickness was enough thin to be observed by HRTEM and Z-contrast STEM, and electron holography. From these comprehensive studies, it was found that piezo electric field of AlGaN in AlGaN/GaN quantum well is considerably small rather than InGaN in InGaN/GaN quantum well, suggesting that minimization of damage layer on the sample surfaces and precise thickness measurement are indispensable.

用电子全息术测量了InGaN/GaN量子阱结构中InGaN层的压电场。该压电场是由InGaN层中沿沿着c轴的晶格应变引起的。我们根据Vegards定律从In组分计算晶格常数，然后估计压电极化。我们从一个晶片上制备了不同厚度的样品。对这些样品进行电子全息照相，评价的内部电场值为0.7±0.2 MV/cm。该值对应于从理论计算估计的In组成4.1±1.3%。另一方面，Z对比STEM观察使我们能够评估In组分4.8± 1.6%，这与电子全息术获得的值一致。对于AlGaN/GaN量子阱结构，我们建立了样品制备技术，例如，采用楔形抛光法和低电压氩离子研磨法对样品进行减薄，使样品厚度为50-100 nm。这个厚度足够薄，可以通过HRTEM和Z-对比STEM以及电子全息术观察到。从这些全面的研究中发现，AlGaN/GaN量子阱中AlGaN的压电电场比InGaN/GaN量子阱中InGaN的压电电场小得多，这表明样品表面上的损伤层最小化和精确的厚度测量是必不可少的。