Collaborative Research: DMREF: Quasi-Direct Semiconductors

非技术描述快速识别具有特定应用特性的材料和结构是材料基因组计划的一个基本方面。该计划成功的一个基本先决条件是能够从材料中的原子组成和配置的基本信息开始预测目标属性。对于太阳能电池、探测器、发光二极管和激光器等设备，关键的设计考虑是在任何特定波长吸收的入射光能的比例。这个DMREF项目关注的是一类特殊的材料，被称为“准直接”半导体，对于这种材料，尚不存在令人满意的光吸收理论。该项目将开发计算准直接半导体光吸收所需的理论工具，并通过在优化的结构中进行光学实验来验证新的理论方法，以精确测量吸收系数。在材料项目数据库中已经发现了200多种准直接半导体，该项目将有可能将这些材料作为未来设备的光学元件。所有发布的代码都将是开源的，以最大限度地发挥社会影响，半导体行业也将受益于该项目提供的训练有素的STEM劳动力。通过与亚利桑那州立大学（ASU）日晷项目（Sundial Project）合作，该项目将重点关注本科生的教育，该项目招募和指导传统上无法进入STEM职业的学生。在德克萨斯大学奥斯汀分校（UT Austin），本科生将直接参与新代码的开发。在准直接半导体中，振动辅助光吸收的能量阈值（所谓的间接间隙）仅略低于直接光吸收的能量阈值（直接间隙）。由于这种接近性，当光子能量接近直接间隙时，振动辅助吸收的量子力学二阶微扰理论表达式会发散，从而导致非物理预测。提出的解决方案包括多体准简并微扰理论的发展和UT Austin团队使用的非微扰特殊位移方法。实验验证需要特殊的样品和材料，因为吸收系数必须在光谱范围内以高精度确定，而光谱范围的变化是数量级的。所需的样品将在亚利桑那州立大学使用定制的化学气相沉积方法制作，光学测量也将由亚利桑那州立大学团队进行。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。

Nontechnical DescriptionThe rapid identification of materials and structures with properties tailored to specific applications is a fundamental aspect of the Materials Genome Initiative. A basic prerequisite for the success of the Initiative is the ability to predict the targeted properties starting from basic information about the atomic composition and configurations in the material. For devices such as solar cells, detectors, light-emitting diodes, and lasers, the key design consideration is the fraction of the incident light energy absorbed at any particular wavelength. This DMREF project focuses on a particular class of materials, dubbed “quasi-direct” semiconductors, for which a satisfactory theory of light absorption does not exist. The project will develop the theoretical tools needed for the calculation of optical absorption in quasi-direct semiconductors and validate the new theoretical methods by carrying out optical experiments in structures optimized for the accurate measurement of the absorption coefficient. More than 200 quasi-direct semiconductors have already been identified in the Materials Project database, and this project will make it possible to incorporate such materials as optical components of future devices. All codes released will be open source to maximize societal impact, and the semiconductor industry will also benefit from the highly trained STEM workforce delivered by the project. A strong educational focus will be placed on undergraduate students by partnering with the Arizona State University (ASU) Sundial Project, which recruits and mentors students who traditionally have limited access to STEM careers. At the University of Texas at Austin (UT Austin), undergraduates will be directly involved in the development of the new codes. Technical DescriptionIn quasi-direct semiconductors, the energy threshold for vibration-assisted light absorption (the so-called indirect gap) is only slightly below the energy threshold for direct light absorption (the direct gap). Because of this proximity, the quantum-mechanical second-order perturbation theory expressions for vibrational-assisted absorption diverge as the photon energy approaches the direct gap, leading to unphysical predictions. The proposed solutions include the development of many-body quasi-degenerate perturbation theory and the use of a non-perturbative special displacement method by the team at UT Austin. The experimental validation requires special samples and materials, since the absorption coefficient must be determined with high accuracy over a spectral range where it changes by orders of magnitude. The needed samples will be fabricated at ASU using custom Chemical Vapor Deposition methods, and the optical measurements will also be performed by the ASU team.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.