Investigation of coherency stress-induced phase separation in AlN/AlxGa1−xN superlattices grown on sapphire substrates,CrystEngComm

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Investigation of coherency stress-induced phase separation in AlN/AlxGa1−xN superlattices grown on sapphire substrates
CrystEngComm ( IF 2.6 ) Pub Date : 2020-03-25 , DOI: 10.1039/d0ce00147c
Weizhen Yao _{1,

2,

3,

4,

5} , Fangzheng Li _{1,

2,

3,

4,

5} , Lianshan Wang _{1,

2,

3,

4,

5} , Sheng Liu _{5,

6,

7,

8,

9} , Hongyuan Wei _{1,

2,

3,

4,

5} , Shaoyan Yang _{1,

2,

3,

4,

5} , Zhanguo Wang _{1,

2,

3,

4,

5}

Affiliation

AlN/AlGaN superlattices (SLs) have been proven promising for various applications including deep ultraviolet light-emitting diodes. However, phase separation in AlGaN of SLs leads to undesirable changes in the optical and electrical properties of SL-based devices. Herein, we investigate the influence of the pulse duration on the compositional structure and surface morphology of the upper AlGaN layer of AlN/AlGaN SLs, grown on a CVD-deposited single crystal AlN template/sapphire substrate by pulsed metal–organic chemical vapor deposition (MOCVD). Spectral transmittance measurements reveal that phase separation happened in the Al_xGa_1−xN layer of SLs with inhomogeneous distribution of the aluminum composition. The coherency stress and strain profiles of AlN/AlGaN SLs were evaluated by finite element simulations. High compressive stress in the upper Al_xGa_1−xN layer and tensile stress in the underlying AlN layer were observed for the SLs with a long pulse duration. This increased stress in SLs facilitates the exclusion of aluminum atoms, thus leading to the apparent phase separation in the upper Al_xGa_1−xN layer of SLs. Additionally, the effect of the shear strain component at the interfaces on the piezoelectric polarization of epitaxial layers was also discussed. This study paves the way for preventing the phase separation during the AlN/AlGaN SL growth by controlling the pulse mode configuration, thereby offering new perspectives for the growth of high-quality AlGaN epitaxial layers targeted for practical applications.

中文翻译：

在蓝宝石衬底上生长的AlN / AlxGa1-xN超晶格中相干应力引起的相分离的研究

已证明AlN / AlGaN超晶格（SLs）在包括深紫外发光二极管在内的各种应用中很有希望。但是，SL的AlGaN中的相分离会导致SL基器件的光学和电学特性发生不良变化。本文中，我们研究了脉冲持续时间对通过脉冲沉积金属-有机化学气相沉积法在CVD沉积的单晶AlN模板/蓝宝石衬底上生长的AlN / AlGaN SLs的上部AlGaN层的组成结构和表面形态的影响（ MOCVD）。光谱透射率测量表明相分离发生在Al _x Ga _{1- x中}N层SL铝成分分布不均匀。通过有限元模拟评估了AlN / AlGaN SLs的相干应力和应变曲线。对于具有长脉冲持续时间的SL，在上层Al _x Ga _{1- x} N层中存在较高的压缩应力，而在其下的AlN层中存在拉伸应力。SL中应力的增加有利于铝原子的排斥，从而导致上部Al _x Ga _1-_x中出现明显的相分离。N层SL。此外，还讨论了界面处的剪切应变分量对外延层压电极化的影响。这项研究为通过控制脉冲模式配置防止在AlN / AlGaN SL生长期间发生相分离铺平了道路，从而为针对实际应用的高质量AlGaN外延层的生长提供了新的视角。

更新日期：2020-03-25

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