Defect Characterization and Control in Metastable GeSn Optoelectronic Alloy Nanostructures

亚稳态 GeSn 光电合金纳米结构的缺陷表征与控制

• 批准号: 2003266
• 负责人: Paul McIntyre
• 金额: $ 48.12万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2003266&HistoricalAwards=false
• 关键词: Defect; Characterization; Control; Metastable; GeSn

Nontechnical DescriptionAn important area of application for semiconductor materials is in optoelectronic devices; for example, in devices such as lasers or light-emitting-diodes (LED’s) that use electrons to stimulate the emission of light. There is great interest, both scientifically and technologically, in semiconductors that can emit light with wavelengths somewhat longer than visible light, i.e. in the mid-infrared part of the spectrum. Such light sources, when fabricated on silicon chips, could become key components in future ubiquitous chemical sensor networks, in speeding up data transfer between and on silicon chips, and in motion sensors required by autonomous vehicles. This research project focuses on a semiconductor material system, germanium-tin, that holds great promise for mid-infrared light emission on silicon chips. The efficiency of light emission by germanium-tin is limited by the presence of atomic scale defects that grow into the material when it is synthesized. This project characterizes the nature and number of such defects, and investigates methods for annihilating or altering them to minimize their effects on germanium-tin. Undergraduates are involved in these research activities, with special efforts made to recruit highly competitive undergraduate researchers from groups that are under-represented in the US science and engineering workforce. The project includes a partnership with Stanford’s RISE outreach program, to inspire high school students to consider further education and careers in STEM fields.Technical DescriptionExhibiting a direct bandgap at sufficiently large (x ~ 10 atomic %) tin composition, Ge(1-x)Sn(x) alloys hold great promise for mid-infrared (IR) light emitters and absorbers, while also being monolithically compatible with silicon electronic and photonic technologies. Previous research on germanium-tin epitaxial films grown on silicon has demonstrated mid-IR optically-pumped lasing, and there has been a gradual trend of increasing Sn content to access longer wavelength operation. The light emission characteristics of Ge(1-x)Sn(x) are still far from optimal. Low growth temperatures ( 300°C) used to promote high Sn content alloys cause large concentrations of acceptor-type vacancy defects to form. Strong pairing of Sn atoms with these vacancies is predicted theoretically and will result in enhanced non-radiative carrier recombination, reducing the efficiency of light emission and absorption. This project uses strain-engineered core-shell nanowire structures as a platform to study post-growth annealing to dissociate Sn-vacancy pairs and to annihilate vacancies incorporated in the Ge(1-x)Sn(x) shells during their growth. Shells of thickness up to 500 nm are of particular interest, to achieve wire structures capable of efficiently guiding mid-IR light. Synchrotron diffuse x-ray scattering is used to characterize trends in the relative concentration of vacancies bound to Sn atoms, divacancies, clusters and monovacancies in the alloys versus annealing time and temperature. A key goal is to understand the rates and mechanisms governing the approach to vacancy equilibrium in these alloys. Extended x-ray absorption fine structure analysis provides an additional probe of local bonding around Sn atoms and the stability of Sn-vacancy pairs. The project also examines atomic fluorine as a chemical vacancy passivant, building on prior experience with F passivation of Si surface states and vacancies in Ge. Coupling between x-ray and optoelectronic characterization of the core-shell wires can reveal fundamental insights into the connection between point defects and device-relevant properties. Temperature-dependent photoluminescence, photoconductivity and ultra-fast pump-probe measurements are used to probe Ge(1-x)Sn(x) band structure and the effects of different vacancy defect populations on carrier recombination dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

半导体材料的一个重要应用领域是光电器件；例如，在使用电子刺激光发射的激光器或发光二极管（LED）等设备中。无论是在科学上还是在技术上，人们都对能够发出比可见光波长稍长的光的半导体产生了极大的兴趣，即在光谱的中红外部分。这种光源在硅芯片上制造后，可能成为未来无处不在的化学传感器网络的关键部件，加速硅芯片之间和硅芯片上的数据传输，以及自动驾驶汽车所需的运动传感器。该研究项目主要研究锗锡半导体材料系统，该系统在硅芯片上发射中红外光方面具有很大的前景。锗锡的发光效率受到合成时生长在材料中的原子尺度缺陷的限制。该项目描述了这些缺陷的性质和数量，并研究了消除或改变它们的方法，以尽量减少它们对锗锡的影响。本科生参与这些研究活动，并特别努力从美国科学和工程劳动力中代表性不足的群体中招募极具竞争力的本科生研究人员。该项目包括与斯坦福大学的RISE外展计划合作，以激励高中生考虑在STEM领域继续教育和职业。Ge(1-x)Sn(x)合金在足够大的（x ~ 10原子%）锡成分下表现出直接带隙，在中红外（IR）光发射器和吸收器中具有很大的前景，同时也与硅电子和光子技术单片兼容。以往在硅上生长的锗锡外延薄膜已经证明了中红外光泵浦激光器，并且有逐渐增加锡含量以获得更长的波长工作的趋势。Ge(1-x)Sn(x)的发光特性还远未达到最佳。采用低生长温度（300℃）促进高锡含量合金，导致大量受体型空位缺陷的形成。从理论上预测了Sn原子与这些空位的强配对，并将导致非辐射载流子复合增强，降低光发射和吸收效率。本项目以应变工程的核壳纳米线结构为平台，研究生长后退火解离Sn空位对，并在生长过程中湮灭Ge(1-x)Sn(x)壳层中的空位。厚度达500纳米的外壳是特别感兴趣的，以实现能够有效引导中红外光的线结构。利用同步辐射x射线散射表征了合金中与锡原子结合的空位相对浓度、空位、团簇和单空位随退火时间和温度的变化趋势。一个关键的目标是了解控制这些合金中空位平衡的速率和机制。扩展的x射线吸收精细结构分析为锡原子周围的局部键和锡空位对的稳定性提供了额外的探测。该项目还研究了氟原子作为化学空位钝化剂，建立在先前的硅表面态和锗空位的F钝化经验的基础上。核心-壳线的x射线和光电子特性之间的耦合可以揭示点缺陷与器件相关特性之间联系的基本见解。利用温度相关的光致发光、光电导率和超快速泵浦探针测量来探测Ge(1-x)Sn(x)的能带结构以及不同空位缺陷族对载流子复合动力学的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Oxide Decomposition and Sn Surface Segregation on Core/Shell Ge/GeSn Nanowires

• DOI: 10.1021/acsaelm.2c01061
• 发表时间: 2022-11
• 期刊: ACS Applied Electronic Materials
• 影响因子: 4.7
• 作者: M. Braun;J. Lentz;Ishaa Bishnoi;A. Meng;L. Casalena;Huikai Cheng;P. McIntyre

Bending and precipitate formation mechanisms in epitaxial Ge-core/GeSn-shell nanowires

• DOI: 10.1039/d1nr04220c
• 发表时间: 2021-10-05
• 期刊: NANOSCALE
• 影响因子: 6.7
• 作者: Meng, Andrew C.;Wang, Yanming;McIntyre, Paul C.
• 通讯作者: McIntyre, Paul C.

Local ordering in Ge/Ge–Sn semiconductor alloy core/shell nanowires revealed by extended x-ray absorption fine structure (EXAFS)

• DOI: 10.1063/5.0136746
• 发表时间: 2023-02
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: J. Lentz;J. Woicik;Matthew Bergschneider;Ryan C. Davis;Aranyak Mehta;Kyeongjae Cho;P. McIntyre