Quasi-transverse optical phonon mode in self-generated semipolar AlN grains embedded in c-oriented AlN matrix grown on sapphire using hydride vapor phase epitaxy
Quasi-transverse optical phonon mode in self-generated semipolar AlN grains embedded in c-oriented AlN matrix grown on sapphire using hydride vapor phase epitaxy
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DOI：
10.1063/1.4951713
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发表时间：
2016-05
影响因子：
3.2
通讯作者：
Y. Hu;Taofei Zhou;S. Zheng;X. H. Liu;J. Zhao;X. Su;J. Huang;Y. Qiu;Jincheng Zhang;Ke Xu
中科院分区：
文献类型：
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作者：
Y. Hu;Taofei Zhou;S. Zheng;X. H. Liu;J. Zhao;X. Su;J. Huang;Y. Qiu;Jincheng Zhang;Ke Xu
在本研究中，我们利用氢化物气相外延技术对蓝宝石上自生氮化铝（AlN）晶粒中的准横向光学声子模式Q（TO）进行了显微光谱研究。通过x射线衍射和透射电镜证实，这些晶粒均嵌埋在(0001)-AlN （c-AlN）外延基体中，外延表面为（10¯1）（s平面）。两束亮场图像进一步显示AlN晶粒无位错。利用角相关偏振拉曼光谱详细讨论了氮化铝颗粒的面内声子各向异性。纯拉曼声子强度随旋转角的变化规律与计算结果吻合较好。Q（TO）声子强度表现出与A1（TO）声子相似的行为，这可以用Loudon公式来解释。然而，观察到的Q（TO）声子的频率波动与纯声子模式的频率波动不同，这不能从经典的Loudon公式中直接理解。提出了一个适用于非正态入射的修正的Loudon公式来解释观测到的Q（to）声子频率波动。结合角相关的拉曼光谱，我们提出了嵌入的半极性AlN晶粒中，随着c-AlN矩阵中不同的面内取向，s面倾角较小导致Q（to）的频率波动。
In this study, we present a microspectroscopic investigation on the quasi-transverse optical phonon modes Q(TO) in some self-generated aluminum nitride (AlN) grains grown on sapphire using hydride vapor phase epitaxy. Using X-ray diffraction and transmission electron microscope, these grains were confirmed to be embedded in (0001)-AlN (c-AlN) epitaxial matrix with an appearance plane of ( 10 1 ¯ 1 ) (s-plane). Two beam bright field images further showed that the AlN grains were free of dislocation. In-plane phonon anisotropy of the AlN grains was discussed in detail using angular-dependent polarized Raman spectroscopy. The dependence of pure Raman phonons intensity on rotation angle agrees well with the calculation. The Q(TO) phonon intensity exhibited similar behavior to that of A1(TO) phonon, which can be explained by Loudon's formula. However, the observed frequency fluctuation for the Q(TO) phonon differs from that of the pure phonon modes, which cannot be directly understood from the classic Loudon's formula. A modified Loudon's formula appropriate to non-normal incidence was presented to explain the observed Q(TO) phonon frequency fluctuation. Combining with the angular-dependent Raman spectra, we proposed that a small inclination of s-plane along with the various in-plane orientations in c-AlN matrix lead to the frequency fluctuation of Q(TO) in these embedded semipolar AlN grains.