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

该奖项支持在可能具有光电应用的新型宽带隙半导体中对点缺陷和掺杂的计算研究。它侧重于II-IV- n2半导体，其中III族元素，例如GaN中的Ga，被II族和IV族元素取代，因此称为杂价三元化合物。在初步工作中，PI发现这些材料具有类似于iii族氮化物的有前途的光电特性。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。两个不同价的阳离子亚晶格所产生的柔性丰富了点缺陷和掺杂物理。PI将与一位研究同种杂价三元化合物的实验员密切合作。该建议的一个组成部分是在两个方面改进当前的点缺陷计算方法。首先，在缺陷物理的背景下，PI将重点关注带隙的低估问题，以及密度泛函理论在局部密度近似中的倾向。利用最近发展的准粒子自洽GW方法的框架，在全势线性化松饼-锡轨道方法中实现，PI将利用在实空间基集中表示自能的可能性，从而减少了大量的计算需求。其次，PI将重点关注与浅供体和浅受体计算精度有关的点缺陷物理中的一个具有挑战性的问题。PI将恢复从第一性原理计算中提取的中心细胞校正的有效质量近似方法，并将该方法推广到所研究的特定类别半导体所需的低对称哈密顿量。为了进一步解决超级单体的有限尺寸效应，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带边缘的单电子缺陷水平，并探索如何将远程库仑尾效应包括在该方法中。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经验计划中的高级项目指导和参与本科生的研究。PI计划与墨西哥的一位同事就该项目的部分内容进行合作，这将允许两个团体之间进行学生交流，并有助于吸引未被充分代表的少数民族从事科学和技术工作。该奖项支持与有意引入晶体材料的孤立缺陷和杂质建模相关的方法开发的计算研究，以及开发的方法和技术在新型半导体中的应用，这些方法和技术可能对操纵电子设备的光学特性有用。孤立的缺陷或杂质，通常称为“点缺陷”，在结晶固体中普遍存在。故意引入的杂质，称为掺杂剂，和天然缺陷，如缺失的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特性方面起着至关重要的作用。有些缺陷对于半导体器件的有效工作是必不可少的，而有些则是有害的。因此，获得对半导体材料中哪些缺陷会产生哪些特性的基本理解是一个与基础和技术相关的问题。虽然理论和计算研究在计算能力的巨大增长和改进的算法发展的帮助下，在过去三十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特性进行准确可靠的预测时，仍然存在某些缺陷。PI将通过重新审视现有的方法，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，来解决在缺陷的结构、电子和光学特性建模中出现的问题。然后，PI将把这些新方法应用于一类由三种元素组成的新型氮化物半导体，这可能有助于克服与现有的由两种元素组成的iii族氮化物相关的某些技术困难，例如氮化镓，用于光学应用。这种新型半导体对于太阳能电池中的光伏能量转换以及通过发光二极管发展固态照明具有重要意义。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经验计划中的高级项目指导和参与本科生的研究。PI计划与墨西哥的一位同事就该项目的部分内容进行合作，这将允许两个团体之间进行学生交流，并有助于吸引未被充分代表的少数民族从事科学和技术工作。

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.