Native Point Defects and Doping of Heterovalent Ternary Wide Band Gap Semiconductors

该奖项支持对一类可能具有光电子应用的新型宽带隙半导体中的点缺陷和掺杂进行计算研究。它集中在II-IV-N_2半导体中，其中III族元素，例如GaN中的Ga被II族和IV族元素取代，因此被称为异价三元系。在初步工作中，PI发现这些材料具有与III族氮化物类似的有前途的光电性能。PI将探索这些II-IV-N2半导体的点缺陷物理是否比III-氮化物更有利于掺杂。具有两个不同价态的阳离子亚晶格所产生的灵活性丰富了点缺陷和掺杂物理。PI将参与与同一系列异价三元化合物的实验者的密切合作。该提案的一个组成部分是在两个领域改进当前的点缺陷计算方法。首先，在缺陷物理的背景下，PI将关注低估带隙的问题，这是密度泛函理论在局域密度近似中的趋势。利用最近发展的准粒子自洽GW方法的框架，如在全势能线性化松饼-锡轨道方法中实现的，PI将利用在实空间基集上表示自能的可能性，从而减少了大量的计算需求。其次，PI将专注于点缺陷物理中的一个具有挑战性的问题，该问题与浅施主和受主计算的准确性有关。PI将恢复从第一性原理计算中提取的中心晶胞修正的有效质量近似方法，并推广对所研究的特定类型的半导体所需的较低对称哈密顿量的方法。为了进一步解决超晶格有限尺寸效应，PI将重新开发格林函数方法，作为一种更准确的方法来获得相对于能带边缘的单电子缺陷能级，并探索如何在这种方法中包括长程库仑尾部效应。该奖项还支持两名研究生在电子结构方法和缺陷物理方面的培训。PI还将通过现有的本科生研究体验计划中的高级项目来指导和参与本科生的研究。国际和平研究所计划与一位来自墨西哥的同事在该项目的部分内容上进行合作，这将允许两个小组之间的学生交流，并有助于吸引未被充分代表的少数族裔进入科学和技术领域。非技术总结该奖项支持与有意引入晶体材料的孤立缺陷和杂质的建模相关的方法开发的计算研究，以及将开发的方法和技术应用于一类新的半导体，这些方法和技术可能有助于操纵电子设备的光学特性。孤立缺陷或杂质，通常被称为“点缺陷”，在晶体固体中普遍存在。故意引入的杂质，称为掺杂剂，以及本征缺陷，如缺失原子或原子在晶体中的错误位置，在决定半导体材料的各种性能方面发挥着非常关键的作用。一些缺陷对半导体器件的有用操作是必不可少的，而另一些则是有害的。因此，从根本上了解哪些缺陷会导致半导体材料中的什么性质，是一个具有基础和技术相关性的问题。虽然理论和计算研究，在计算能力的巨大增加和改进的算法发展的帮助下，在过去30年中为实现这一目标发挥了重要作用，但即使是最广泛使用的无参数计算方法，在对固体中天然缺陷和杂质的各种性质进行准确可靠的预测时，也仍然存在某些不足。PI将通过重新审视现有方法，将它们与最先进的能力相结合，并扩展它们以产生更复杂的工具和方法，从而提高无参数缺陷计算的准确性和可靠性，从而解决缺陷的结构、电子和光学属性建模中出现的此类问题。然后，PI将把这些新方法应用于由三种元素组成的一类新的氮化物半导体，这可能有助于克服与现有的III族氮化物相关的某些技术困难，这些氮化物由两种元素组成，如用于光学应用的氮化镓。这种新型半导体对太阳能电池中的光伏能量转换以及发光二极管固态照明的发展具有重要意义。如果成功，该项目将为这些材料的进一步实验开发提供理论基础。该奖项还支持对两名研究生进行电子结构方法和缺陷物理方面的培训。PI还将通过现有的本科生研究体验计划中的高级项目来指导和参与本科生的研究。国际和平协会计划与墨西哥的一位同事就该项目的部分内容进行合作，这将使这两个群体之间进行学生交流，并有助于吸引代表人数较少的少数族裔进入科学和技术领域。

TECHNICAL SUMMARY This award supports computational research on point defects and doping in a new class of wide band gap semiconductors which may have optoelectronic applications. It focuses on II-IV-N2 semiconductors in which the group III element, e.g. Ga in GaN, is replaced by group II and group IV elements, hence the name heterovalent ternary. In preliminary work, the PI found that these materials have promising optoelectronic properties similar to those of the group-III nitrides. The PI will explore whether the point defect physics of these II-IV-N2 semiconductors is more conducive to doping than the III-nitrides. The flexibility arising from having two cation sublattices with different valences enriches the point defect and doping physics. The PI will participate in a close collaboration with an experimentalist who works on the same family of heterovalent ternary compounds.An integral part of the proposal is to improve current methodologies for point defect calculations in two areas. First, in the context of defect physics, the PI will focus on the problem of underestimating the band gaps, as is the tendency of density functional theory in the local density approximation. Using the framework of the recently developed quasiparticle self-consistent GW approach as implemented in the full-potential linearized muffin-tin orbital method, the PI will exploit the possibility of representing the self-energy in a real-space basis set, hence reducing the large computational demand. Second, the PI will focus on a challenging problem in point defect physics related to the accuracy of the calculations for shallow donors and acceptors. The PI will revive the effective mass approximation method with central cell corrections extracted from first-principles calculations and generalize the approach to the lower symmetry Hamiltonian required for the particular class of semiconductors under study. To further address the supercell finite size effects, the PI will redevelop the Green's function approach as a more accurate means to obtain one-electron defect levels with respect to the band edges and explore how long-range Coulomb tail effects can be included in this method.The award also supports the training of two graduate students in electronic structure methods and defect physics. The PI will also mentor and involve undergraduate students in research through senior projects in an existing Research Experience for Undergraduates program. The PI's planned collaboration with a colleague from Mexico on parts of this project will allow student exchanges between the two groups and be useful in attracting underrepresented minorities to science and technology.NONTECHNICAL SUMMARYThis award supports computational research on method development related to modeling of isolated imperfections and impurities that are intentionally introduced into crystalline materials as well as the application of the developed methods and techniques to a new class of semiconductors that can be potentially useful for manipulating optical properties of electronic devices.Isolated imperfections or impurities, generally called "point defects", are ubiquitous in crystalline solids. Intentionally introduced impurities, called dopants, and native defects, such as missing atoms or atoms in the wrong place in the crystal, play very crucial roles in determining various properties of semiconducting materials. Some defects are essential for, while some are detrimental for the useful operation of a semiconductor device. Accordingly, obtaining a fundamental understanding of which defects give rise to what properties in semiconductor materials is a problem of both fundamental and technological relevance. While theoretical and computational studies, aided by the vast increase in computational power and improved algorithmic developments, have played a major role toward achieving this goal during the last three decades, even the most widely used parameter-free computational methods still suffer from certain deficiencies when it comes to making accurate and reliable predictions about various properties of native defects and impurities in solids. The PI will address such problems that arise in the modeling of structural, electronic, and optical properties of defects by revisiting existing methodologies, combining them with state-of-the-art capabilities, and extending them to produce more sophisticated tools and methods that can increase the accuracy and reliability of parameter-free defect computations. The PI will then apply these new methods to a new class of nitride semiconductors, composed of three elements, that can potentially help to overcome certain technological difficulties associated with existing group-III nitrides, which are composed of two elements, such as gallium nitride, for optical applications. This new class of semiconductors is important for photovoltaic energy conversion in solar cells as well as the development of solid-state lighting by light emitting diodes. If successful, the project will provide a rationale for further experimental development of these materials. The award also supports the training of two graduate students in electronic structure methods and defect physics. The PI will also mentor and involve undergraduate students in research through senior projects in an existing Research Experience for Undergraduates program. The PI's planned collaboration with a colleague from Mexico on parts of this project will allow student exchanges between the two groups and be useful in attracting underrepresented minorities to science and technology.