Epitaxial twin coupled microstructure in GeSn films prepared by remote plasma enhanced chemical vapor deposition

Jiechao Jiang, N. Chetuya, Joseph H. Ngai, Gordon J. Grzybowski, E. Meletis, Bruce Claflin
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Abstract

Growth of GeSn films directly on Si substrates is desirable for integrated photonics applications since the absence of an intervening buffer layer simplifies device fabrication. Here, we analyze the microstructure of two GeSn films grown directly on (001) Si by remote plasma-enhanced chemical vapor deposition (RPECVD): a 1000 nm thick film containing 3% Sn and a 600 nm thick, 10% Sn film. Both samples consist of an epitaxial layer with nano twins below a composite layer containing nanocrystalline and amorphous. The epilayer has uniform composition, while the nanocrystalline material has higher levels of Sn than the surrounding amorphous matrix. These two layers are separated by an interface with a distinct, hilly morphology. The transition between the two layers is facilitated by formation of densely populated (111)-coupled nano twins. The 10% Sn sample exhibits a significantly thinner epilayer than the one with 3% Sn. The in-plane lattice mismatch between GeSn and Si induces a quasi-periodic misfit dislocation network along the interface. Film growth initiates at the interface through formation of an atomic-scale interlayer with reduced Sn content, followed by the higher Sn content epitaxial layer. A corrugated surface containing a high density of twins with elevated levels of Sn at the peaks begins forming at a critical thickness. Subsequent epitaxial breakdown at the peaks produces a composite containing high levels of Sn nanocrystalline embedded in lower level of Sn amorphous. The observed microstructure and film evolution provide valuable insight into the growth mechanism that can be used to tune the RPECVD process for improved film quality.
远程等离子体增强化学气相沉积法制备的 GeSn 薄膜中的外延孪晶耦合微结构
直接在硅衬底上生长 GeSn 薄膜是集成光子学应用的理想选择,因为没有中间缓冲层可以简化器件制造。在此,我们分析了通过远程等离子体增强化学气相沉积 (RPECVD) 技术直接在 (001) 硅上生长的两层 GeSn 薄膜的微观结构:一层 1000 nm 厚、含 3% 锡的薄膜和一层 600 nm 厚、含 10% 锡的薄膜。这两种样品都由一个纳米孪晶外延层组成,外延层下面是一个包含纳米晶和非晶的复合层。外延层具有均匀的成分,而纳米晶材料的含 Sn 量高于周围的非晶基质。这两层被一个具有明显丘陵形态的界面隔开。两层之间的过渡是通过形成密集的(111)耦合纳米孪晶来实现的。与含锡量为 3% 的样品相比,含锡量为 10% 的样品的外延层明显更薄。GeSn 和硅之间的面内晶格失配导致了沿界面的准周期错配位错网络。薄膜的生长始于界面上形成的原子尺度的锡含量较低的中间层,然后是锡含量较高的外延层。在临界厚度处开始形成包含高密度孪晶的波纹表面,峰值处的锡含量升高。随后在峰值处的外延击穿产生了一种复合材料,其中含有高含量的锡纳米晶和较低含量的锡非晶。观察到的微观结构和薄膜演化过程为了解生长机制提供了宝贵的信息,可用于调整 RPECVD 工艺以提高薄膜质量。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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