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生长温度对使用激光MBE在a-平面蓝宝石上制备的外延GaN薄膜的结构和光学性质的影响

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发表于 2018-5-31 09:09:04 | 显示全部楼层 |阅读模式
Influence of growth temperature on structural and optical properties of laser MBE grown epitaxial thin GaN films on a-plane sapphire
生长温度对使用激光MBE在a-平面蓝宝石上制备的外延GaN薄膜的结构和光学性质的影响
Journal of Vacuum Science & Technology B 36, 04G102 (2018);

https://doi.org/10.1116/1.5025126

Chodipilli Ramesh and Prashant Tyagi
  CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India and Academy of Scientific and Innovative Research, CSIR-NPL Campus, Dr. K. S. Krishnan Road, New Delhi 110012, IndiaSandeep Singh and Preetam Singh
  CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, IndiaGovind Gupta, Kamlesh Kumar Maurya, Kuchibhotla Murali Krishna Srivatsa, Muthusamy Senthil Kumar, and Sunil Singh Kushvahaa)
  CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India and Academy of Scientific and Innovative Research, CSIR-NPL Campus, Dr. K. S. Krishnan Road, New Delhi 110012, India
more...Hide Affiliations
a)Author to whom correspondence should be addressed; electronic mail: kushvahas@nplindia.org

ABSTRACT
摘要

Epitaxial thin GaN films (~60 nm) have been grown on a-plane sapphire substrates at different growth temperatures (500–700 °C) using laser molecular beam epitaxy (LMBE). The effect of growth temperatures on the structural and optical properties of GaN layers grown on low temperature (LT) GaN buffer on prenitridated a-sapphire have been studied systematically. The in situ reflection high energy electron diffraction pattern revealed the three-dimensional epitaxial growth of GaN films on a-sapphire under the adopted growth conditions. The full width at half maximum (FWHM) value of x-ray rocking curves (XRCs) along GaN (0002) and (10-12) planes decreases with increasing growth temperature. The FWHM values of (0002) and (10-12) XRC for the 700 °C grown GaN film are 1.09° and 1.08°, respectively. Atomic force microscopy characterization showed that the grain size of GaN increases from 30–60 to 70–125 nm with the increase in growth temperature as GaN coalescence time is shorter at high temperature. The refractive index value for the dense GaN film grown at 600 °C is obtained to be ~2.19 at the wavelength of 632 nm as deduced by spectroscopic ellipsometry. Photoluminescence spectroscopy confirmed that the epitaxial GaN layers grown on a-sapphire at 600–700 °C possess near band edge emission at ~3.39 eV, close to bulk GaN.
The GaN growth at 700 °C without a buffer still produced films with better crystalline and optical properties, but their surface morphology and coverage were inferior to those of the films grown with LT buffer. The results show that the growth temperature strongly influences the structural and optical quality of LMBE grown epitaxial GaN thin films on a-plane sapphire, and a growth temperature of >600 °C is necessary to achieve good quality GaN films.


        使用激光分子束外延(LMBE)在不同生长温度(500-700℃)下在a平面蓝宝石衬底上生长了外延薄GaN膜(约60nm)。作者系统地研究了生长温度对生长在低温(LT)GaN缓冲层上的GaN层的结构和光学性质的影响,该GaN缓冲层是沉积在经过预氮化的a-蓝宝石上。原位反射高能电子衍射图案揭示了在所采用的生长条件下在a-蓝宝石上的GaN薄膜的三维外延生长。沿着GaN(0002)和(10-12)平面的X射线摇摆曲线(XRCs)的半峰全宽(FWHM)值随着生长温度的增加而降低。在700 °C下生长的GaN膜的(0002)和(10-12)XRC的FWHM值分别为1.09°和1.08°。原子力显微镜的表征表明,随着生长温度的增加,GaN的晶粒尺寸从30-60增加到70-125nm,这是因为在高温下GaN聚结时间较短。由光谱椭偏仪推导出,在600 °C下生长的致密GaN膜的折射率值在632nm波长处为约2.19。光致发光光谱证实,在600-700℃在a-蓝宝石上生长的外延GaN层在〜3.39eV附近具有近带边发射,接近体材料GaN。没有缓冲层的700 °C下生长的GaN仍然能产生具有更好结晶性和光学性质的膜层,但是其表面形态和覆盖度低于使用了LT缓冲层生长的薄膜。所得的结果表明,生长温度对在平面蓝宝石上使用LMBE生长的外延GaN薄膜的结构和光学性质有很大影响,生长温度 >600 °C对于获得高质量的GaN薄膜是必要的条件。


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