New forms of silicon with enhanced optoelectronic properties

非技术描述：与自由导电的金属不同，半导体需要能量输入来促进电子进入导电状态。最小输入能量，称为带隙，直接或间接取决于特定的晶体结构。硅是绝大多数现代电子产品和太阳能设备所必需的，它具有间接带隙，这意味着光的吸收和发射是微弱的过程。相反，直接带隙材料是有效的光吸收和发射体。最近的理论计算表明，许多形式的晶体硅具有直接带隙的能量可行性，但实验合成途径是不可用的。该研究小组旨在创造具有直接带隙的全新形式的晶体硅，以改善光电性能，影响包括固态探测器，光通信和能量转换设备在内的一系列技术。研究的重点是结合高压和低压实验的新型合成途径，以达到动力学稳定状态。更一般地说，新的合成方法的发展广泛地影响了硅以外的亚稳材料。这个研究项目发生在一个强调学生和博士后学者职业发展的教育环境中。技术描述：本项目采用高压/常压混合合成亚稳材料的新方法。在基态的30 kJ/mol范围内，预计存在许多具有增强光电性能的亚稳态硅同素异体，但缺乏有效的合成途径。通过在高压条件下形成的前驱体引发常压化学合成，由于回收的前驱体在环境条件下处于亚稳态的高能状态，全新的合成途径成为可能。这项工作探索了硅中可实现材料的深度，并探索了亚稳同素异形体和光电子特性之间的关系，以创造具有直接或准直接带隙的全新亚稳晶体同素异形体。该研究有助于解决立方金刚石结构的间接带隙长期存在的局限性。实验在高压条件下进行，以优化单晶生长，在低压条件下进行，以优化前驱体转化。通过实验建立了新型硅同素异形体的本征光学和电子输运性质，并通过基于密度泛函理论的结构搜索计算支持了潜在高压前驱体材料库。该项目的总体目标是生产和表征具有改进光学活性的新硅相。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 description: Unlike metals that freely conduct electricity, semiconductors require energy input to promote electrons into conducting states. The minimum input energy, known as the band gap, is either direct or indirect depending on the specific crystalline structure. Silicon, which is essential for the vast majority of modern electronics and solar energy devices, possesses an indirect band gap meaning that light absorption and emission are feeble processes. In contrast, direct band gap materials are effective absorbers and emitters of light. Recent theoretical calculations indicate energetic feasibility for numerous forms of crystalline silicon with direct band gaps, but experimental synthesis pathways are not available. This research team aims to create entirely new forms of crystalline silicon that possess direct band gaps in order to improve optoelectronic properties that impact a range of technologies including solid-state detectors, optical communication and energy conversion devices. Research is focused on novel synthetic pathways that combine high- and low-pressure experiments in order to achieve access to kinetically-stabilized states. More generally, the development of novel synthesis methodologies broadly affects metastable materials beyond silicon. This research project occurs within an educational environment that emphasizes the career development of students and postdoctoral scholars. Technical description: This project utilizes a new approach for metastable materials synthesis through a combined high-pressure / ambient-pressure hybrid method. Numerous metastable silicon allotropes with enhanced optoelectronic properties are predicted to exist within 30 kJ/mol of the ground state, but effective synthesis pathways are lacking. By initiating ambient-pressure chemical synthesis from precursors formed under high-pressure conditions, entirely new synthesis pathways are possible due to the high-energy state of the recovered precursor that is metastable at ambient conditions. This effort explores the depth of realizable materials in silicon and probes the relationships between metastable allotropes and optoelectronic properties in order to create entirely new metastable crystalline allotropes that possess direct or quasidirect band gaps. The research contributes to the longstanding limitations associated with the indirect band gap of the cubic diamond structure. Experiments are conducted at high-pressure conditions in order to optimize single-crystalline growth and at low-pressure conditions to optimize precursor transformations. The intrinsic optical and electronic transport properties of novel silicon allotropes are established experimentally, and the library of potential high-pressure precursor materials is supported by calculations including density functional theory-based structure searching. The overall goal of the project is to produce and characterize new silicon phases exhibiting improved optical activity.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.