Analysis of GaN decomposition in an atmospheric MOVPE vertical reactor
Analysis of GaN decomposition in an atmospheric MOVPE vertical reactor
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DOI：
10.1002/pssc.200673509
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
W. Fathallah;T. Boufaden;B. Jani
中科院分区：
文献类型：
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作者：
W. Fathallah;T. Boufaden;B. Jani
在常压金属有机气相外延(AP-MOVPE)垂直反应器中，研究了GaN的分解随退火气氛(H2，N2+H2)的变化。为了解释在立式反应器中用2D缓冲层在氢气和氮气混合气氛下在氧化铝衬底上生长高温GaN(HT-GaN)失败的原因，对垂直和水平反应器中低温GaN(LT-GaN)的分解进行了比较。使用实时激光反射仪测量了分解速率随温度和环境气体的变化。用扫描电子显微镜(SEM)对薄膜的表面进行了分析。即使在氨气和氮气存在的情况下，氢似乎也通过在衬底表面的质量传输、扩散和分解过程来显著影响LT-GaN的表面形貌。与高温GaN相比，LT-GaN的高分解速率归因于层的类非晶态结构和Ga-N键的不稳定性。这有利于在这一层分解开始时出现镜面状的镓表面。液态镓的存在催化分解过程。HT-GaN扫描电子显微镜分析表明，“完全”分解的GaN表面主要是由镓液滴组成。这些都被移除了。这些液滴周围和下面的区域被一层类似于GaN的多孔薄膜所覆盖。聚结的镓液滴可能覆盖了部分分解的GaN的某些区域，并保护它们免受H2的攻击和完全分解。(2007 Wiley-VCH Verlag GmbH&Co.KGaA，Weinheim)
The GaN decomposition versus the annealing ambient (H2, N2 + H2) have been investigated in atmospheric pressure metal organic vapor phase epitaxy (AP-MOVPE) vertical reactor. A comparison between the low temperature GaN (LT-GaN) decomposition in a vertical reactor and a horizontal one was discussed in order to explain the failure of high temperature GaN (HT-GaN) growth on Al2O3 using 2D buffer layer under a mixture of H2 and N2 in our vertical reactor. Decomposition rates versus temperature and ambient gas were measured using real time laser reflectometry. The surfaces of these films were analyzed using a scanning electron microscopy (SEM). Hydrogen seems to considerably affect the LT-GaN surface morphology by a mass transport, diffusion on the substrate surface and by a decomposition process even in the presence of ammonia and nitrogen. The high decomposition rates of the LT-GaN measured in comparison to that determined for the HT-GaN one is attributed to the amorphous-like structure of the layer and the instability of Ga-N bonds. This favors the appearance of a mirror-like gallium surface in the beginning of this layer decomposition. The presence of liquid gallium catalyzes the decomposition process. HT-GaN SEM analysis revealed that the surface of the “totally” decomposed GaN surface is dominated by gallium droplets. These were removed. The region around and under these droplets is capped by a porous like GaN film. The coalesced gallium droplets may cover some areas of partially decomposed GaN and preserve them from H2 attack and total decomposition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)