Kouvetakis John, Wallace Patrick M, Xu Chi, Ringwala Dhruve A, Mircovich Matthew, Roldan Manuel A, Webster Preston T, Grant Perry C, Menéndez José
School of Molecular Science, Arizona State University, Tempe, Arizona 85287-1604, United States.
Department of Physics, Arizona State University, Tempe, Arizona 85287-1504, United States.
ACS Appl Mater Interfaces. 2023 Oct 18;15(41):48382-48394. doi: 10.1021/acsami.3c10230. Epub 2023 Oct 6.
A systematic effort has been described to grow ternary GeSiSn semiconductors on silicon with high Sn concentrations spanning the 9.5-21.2% range. The ultimate goal is not only to produce direct band gap materials well into the infrared region of the spectrum but also to approach a critical concentration () for which further additions of Si would decrease─rather than increase─the band gap. This counterintuitive behavior is expected as a result of the giant bowing parameter in the compositional dependence of the band gap associated with the presence of Si-Sn pairs. The growth approach in this study was based on a chemical vacuum deposition method that uses SiH, GeH, and SnD or SnH as the sources of Si, Ge, and Sn, respectively. A fixed Si concentration near = 0.05-0.07 was chosen to focus the exploration of the compositional space. A first family of samples was grown of Ge-buffered Si substrates. For Sn concentrations < 0.12, it was found that the samples relaxed their mismatch strain in situ during growth, resulting in high Sn content films that had relatively low levels of strain and exhibited photoluminescence signals that demonstrated direct band gap behavior for the first time. The device potential of these materials was also demonstrated by fabricating a prototype photodiode with low dark currents. The optical studies suggest that the above-mentioned critical concentration is close to = 0.2. As the growth temperature was lowered in an effort to reach such values, Sn concentrations as high as = 0.15 were obtained, but the films grew fully strained with compressive levels as high as 1.7%. To increase the Sn concentration beyond = 0.15, a new strategy was adopted, in which the Ge buffer layer was eliminated, and the ternary alloy was grown directly on Si. The much higher lattice mismatch between the GeSiSn layer and the Si substrate caused strain relaxation right at the film/substrate interface, and the subsequent films grew with much lower levels of strain. This made it possible to lower the growth temperatures even further and achieve a comprehensive series of strained relaxed samples with tunable Sn concentrations as high as = 0.21 (and beyond). The latter represent the highest Sn contents in crystalline GeSiSn attained to date and reach the desired = 0.2 range. The synthesized films exhibited significant thickness, allowing a thorough determination of composition, crystallinity, morphology, and bonding properties, indicating the formation of single-phase single-crystal alloys with random cubic structures. Further work will focus on optimizing the latter samples to explore the optical and electronic properties.
已有研究描述了一种系统性的努力，即在硅上生长三元锗硅锡半导体，其锡浓度范围跨度为9.5%至21.2%。最终目标不仅是制造出光谱红外区域内具有直接带隙的材料，还要接近一个临界浓度（），超过该浓度后进一步添加硅会减小而非增大带隙。由于与硅 - 锡对的存在相关的带隙成分依赖性中存在巨大的弯曲参数，预计会出现这种与直觉相反的行为。本研究中的生长方法基于一种化学气相沉积法，该方法分别使用硅烷（SiH）、锗烷（GeH）和锡氘（SnD）或锡烷（SnH）作为硅、锗和锡的源。选择固定的硅浓度接近 = 0.05 - 0.07，以聚焦成分空间的探索。第一组样品是在锗缓冲的硅衬底上生长的。对于锡浓度 < 0.12，发现样品在生长过程中就地弛豫其失配应变，从而得到具有相对低应变水平的高锡含量薄膜，并首次表现出显示直接带隙行为的光致发光信号。通过制造具有低暗电流的原型光电二极管，也证明了这些材料的器件潜力。光学研究表明，上述临界浓度接近 = 0.2。为了努力达到该值而降低生长温度时，获得了高达 = 0.15的锡浓度，但薄膜生长时完全应变，压缩应变水平高达1.7%。为了将锡浓度提高到超过 = 0.15，采用了一种新策略，即去除锗缓冲层，直接在硅上生长三元合金。锗硅锡层与硅衬底之间更高的晶格失配导致在薄膜/衬底界面处立即发生应变弛豫，随后的薄膜以低得多的应变水平生长。这使得进一步降低生长温度并获得一系列全面的具有高达 = 0.21（及更高）可调锡浓度的应变弛豫样品成为可能。后者代表了迄今为止在结晶锗硅锡中获得的最高锡含量，并达到了所需的 = 0.2范围。合成薄膜具有显著的厚度，从而能够全面确定成分、结晶度、形态和键合性质，表明形成了具有随机立方结构的单相单晶合金。进一步的工作将集中于优化后一组样品，以探索其光学和电子性质。
