Thermal stability of ε-Ga2O3 polymorph
Thermal stability of ε-Ga2O3 polymorph
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DOI：
10.1016/j.actamat.2017.08.062
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发表时间：
2017-11-01
期刊：
影响因子：
9.4
通讯作者：
Bosi, M.
中科院分区：
文献类型：
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作者：
Fornari, R.;Pavesi, M.;Bosi, M.
采用互补方法研究了ε-Ga_2 O_3多晶型的热稳定性。在700-1000摄氏度范围内的温度下退火，然后通过X射线衍射（XRD）和透射电子显微镜（TEM）研究在c取向蓝宝石上生长的ε-Ga 2 O3外延膜。此外，差示扫描量热法（DSC）高达1100摄氏度的纯epsilon-Ga 2 O3的碎片从一个非常厚的层进行。结果清楚地表明，ε-Ga 2 O3在650 ℃以上开始改变其晶体结构，如DSC曲线的温和吸热弯曲所示。然而，取决于DSC加热速率，在880-900摄氏度下相当突然地发生向β相的有效转变。XRD和TEM结果证实了这一证据。TEM研究特别表明，在1000 ℃退火和快速冷却后，薄膜完全由β-Ga 2 O3晶粒组成，其中大多数相对于蓝宝石衬底具有（310）取向。然而，如果冷却速率显著降低，则转化的β-Ga 2 O 3层呈现平行于Al 2 O 3衬底的（00.1）的标准取向（-201）。基于这项研究的结果，我们得出结论，ε-Ga 2 O 3可以方便地用于器件制造，利用其更高的晶体对称性和更好的匹配蓝宝石。然而，所有制造步骤必须在低于700摄氏度的温度下进行。(C)2017 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
The thermal stability of epsilon-Ga2O3 polymorph was studied by complementary methods. Epitaxial films of epsilon-Ga2O3 grown on c-oriented sapphire were annealed at temperatures in the range 700-1000 degrees C and then investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). In addition, Differential Scanning Calorimetry (DSC) up to 1100 degrees C was carried out on fragments of pure epsilon-Ga2O3 taken from a very thick layer. The results clearly indicate that epsilon-Ga2O3 initiates modifying its crystallographic structure above 650 degrees C as demonstrated by a mild endothermic bent of the DSC curves. However, the effective transition to beta-phase occurs quite suddenly at 880-900 degrees C, depending of the DSC heating rate. XRD and TEM results confirm this evidence. TEM investigation in particular shows that after annealing at 1000 degrees C and rapid cooling the film is completely made of beta-Ga2O3 grains, most of them with orientation (310) respect to the sapphire substrate. However, if the cooling rate is substantially reduced, the converted beta-Ga2O3 layer assumes the standard orientation (-201) parallal to (00.1) of the Al2O3 substrate. Based on the results of this study we conclude that epsilon-Ga2O3 may conveniently be used for device fabrication, exploiting its higher crystallographic symmetry and better matching to sapphire. However, all fabrication steps must be carried out at temperatures below 700 degrees C. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.