Defect calculations in Ga-based semiconductors using optimal hybrid functionals

使用最佳混合函数计算镓基半导体中的缺陷

• 批准号: 394149042
• 负责人: Professor Dr. Thomas Frauenheim
• 金额: --
• 依托单位: Bremen Center for Computational Materials Science (BCCMS)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/394149042?language=en
• 关键词: Defect; calculations; Ga; based; semiconductors

The functionality of semiconductors is closely connected to their point defects, which control the electronic and optical behavior of the material. The emphasis of defect physics has shifted in recent years from micro- to optoelectronics and photovoltaics, i.e., from the traditional elemental and binary semiconductors, with relatively narrow gap, to wide band gap materials of more complicated structures. Electronic structure calculations in these materials have revealed that local and semi-local approximations to density functional theory (DFT) cannot be trusted: partly because the bigger error in the width of the band gap but also because of the artificial delocalization of defect states (which, make the defect level shallower and preclude the reproduction of small polaron states). While first-principles total energy calculations beyond (semi)local DFT cannot yet be carried out for supercells, we have shown that the HSE06 screened hybrid functional yields very accurate results for defects in C, Si, SiC, Ge and TiO2. We have suggested that the success is connected to the fact that HSE06 in these materials provides the total energy as an appropriate piece-wise linear function of the occupation numbers, because of error compensation between semi-local and Hartree-Fock exchange.Gallium based semiconductors have immense technological importance: besides the GaN LEDs, Ga2O3 has also great potential for application as UV-transparent electrode and se-miconductor for power MOSFETs, and Ga-based chalcopyrites (CuGaS2, CuGaSe2) are considered in photovoltaics. HSE06 underestimates the band gap of these materials and we have recently shown that simple tuning of the mixing parameter to correct that (as usual in the literature), does not lead to correct defect levels. Tuning the mixing and the screening parameters, to reproduce the gap and to fulfill the generalized Koopman theorem, has allowed us to achieve the correct piece-wise linear behavior of the total energy as a function of the occupation numbers and, consequently, the accurate description of defect states. Of course, this procedure leads to material specific parameters. The aim of this project is twofold: on the one hand we would like to investigate the trends in the optimal parameters across the Ga-based semiconductors mentioned above (but also for CuInS2 and CuInSe2), in order to establish general rules for finding a screened hybrid for a class of materials and, on the other, perform accurate calculations to identify important defect centers in these materials.

半导体的功能与其点缺陷密切相关，点缺陷控制着材料的电子和光学行为。近年来，缺陷物理学的重点已经从微电子学转移到光电子学和光电子学，即，从具有相对窄的带隙的传统元素和二元半导体到具有更复杂结构的宽带隙材料。这些材料的电子结构计算表明，密度泛函理论（DFT）的局部和半局部近似是不可信的：部分原因是带隙宽度的误差较大，但也因为缺陷态的人为离域（使缺陷能级变浅，并阻止小极化子态的再生）。虽然第一原理总能量计算超出（半）本地DFT还不能进行超晶胞，我们已经表明，HSE 06筛选的混合功能产生非常准确的结果，在C，Si，SiC，Ge和TiO 2的缺陷。我们认为，这一成功与以下事实有关：由于半局域和Hartree-Fock交换之间的误差补偿，这些材料中的HSE 06提供的总能量是占据数的适当分段线性函数。镓基半导体具有巨大的技术重要性：Ga_2O_3除了用作GaN发光二极管外，还具有很大的应用潜力，可用作功率MOSFET的紫外透明电极和半导体（CuGaS 2，CuGaSe 2）被认为是在光化学。HSE 06低估了这些材料的带隙，我们最近已经证明，简单地调整混合参数来纠正（如文献中常见的那样），不会导致正确的缺陷能级。调整的混合和屏蔽参数，以重现差距和履行广义库普曼定理，使我们能够实现正确的分段线性行为的总能量作为占领数的函数，因此，准确描述的缺陷状态。当然，该过程导致材料特定的参数。该项目的目的是双重的：一方面，我们希望研究上述Ga基半导体（以及CuInS 2和CuInSe 2）的最佳参数趋势，以建立寻找一类材料的筛选混合物的一般规则，另一方面，进行精确计算以确定这些材料中的重要缺陷中心。