Engineering Band Gap Energy Through Structural Motifs in Nitride Semiconductors

非技术概述半导体材料构成了几乎所有电子产品的基础，从太阳能电池和固态照明，到微处理器等复杂集成电路。然而，尽管进行了一个世纪的调查，研究人员仍在这一领域取得根本性的发现--这些发现有助于提高设备性能、降低制造成本或简化与其他技术的集成。该项目活动是基于研究团队的一项出人意料的发现，即半导体材料的基本性质直接源于原子尺度的结构基元，而不是普遍接受的偏离周期性。通过改变这种观点，有可能实现比以前认识到的参数值范围大得多的范围。其结果是为特定应用选择材料的一种全新方法。该项目还包括为中学生和教师开展推广活动，通过调查人工智能/机器学习技术如何应用于图像识别和数据分析，让社区直接参与到该项目中，从而帮助确保在科学/技术/工程/数学(STEM)领域拥有多样化和积极的年轻学生池。技术总结作为先前一项关于阳离子无序如何改变地球上丰富的元素、可持续来源的三元异价半导体ZnSnN的带隙能量的研究的一部分，研究小组发现结构基元在确定这一最基本的半导体参数方面发挥了意想不到的作用。精心设计的实验表明，不仅有可能通过系统地改变组成晶格的基元的类型和浓度来关闭这种材料的带隙，而且还有可能获得与反转带相对应的“负”带隙能量。此外，初步证据表明，在其他化合物半导体中也可能产生同样的效果，包括具有重要商业意义的InGaN材料系列，同样是通过结构基元的作用。该项目使用等离子体辅助分子束外延生长晶体，结合光学吸收、霍尔效应、电子和X射线衍射技术的补充套件，调查了这两个氮基材料系统的全部可实现的带隙能量，以期了解对电荷载流子传输、光学性质以及最终设备材料选择的影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical SummarySemiconductor materials form the basis for practically all electronics, from solar cells and solid state lighting, to complex integrated circuits such as microprocessors. Nevertheless, despite a century of investigation, researchers are still making fundamental discoveries in this field – discoveries which lead to improved device performance, reduced manufacturing cost, or streamlined integration with other technologies. The project activity is based on the unexpected discovery by the research team that the fundamental properties of semiconductor materials stem directly from atomic-scale structural motifs, and not deviations from periodicity as is generally accepted. By shifting that viewpoint, it is possible to achieve a much larger range of parameter values than previously realized. The result is a completely new approach to selecting materials for specific applications. The project also incorporates development of outreach activities for both middle school children and teachers, involving the community directly in the project by investigating how artificial intelligence/machine learning techniques are applied to image recognition and data analysis, thereby helping to ensure a diverse and motivated pool of young students for careers in science/technology/engineering/math (STEM) fields.Technical SummaryAs part of a previous study on how cation disorder changes the band gap energy of the earth abundant element, sustainably-sourced ternary heterovalent semiconductor ZnSnN2, the research team has discovered the unexpected role played by structural motifs in determining this most fundamental of all semiconductor parameters. Carefully designed experiments indicate that it is not only possible to close the band gap of this material through systematic variation of the type and concentration of motifs that make up the lattice, but it is also possible to access "negative" band gap energies, corresponding to inverted bands. Further, preliminary evidence indicates that the same effect is possible in other compound semiconductors, including the commercially important InGaN family of materials, again through the action of structural motifs. The project investigates the full range of achievable band gap energies of both of these nitrogen-based material systems using plasma-assisted molecular beam epitaxy based crystal growth in conjunction with a complementary suite of optical absorption, Hall effect and electron and x-ray diffraction techniques, with a view towards understanding the ramifications for charge carrier transport, optical properties, and ultimately material selection choices for devices.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.