Nazir Safdar, Bernal Camille, Yang Kesong
Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States.
ACS Appl Mater Interfaces. 2015 Mar 11;7(9):5305-11. doi: 10.1021/am508662q. Epub 2015 Feb 25.
The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)(+1)/(TiO2)(0) interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d(1) orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett. 2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyz and dxz orbitals.
在极性/非极性的氧化镧铝/钛酸锶（LAO/STO）异质结构中形成的高迁移率二维电子气（2DEG）因其在纳米级固态器件中的潜在应用而备受关注。为了在器件设计中实现二维电子气的实际应用，需要诸如可调电荷载流子密度和迁移率等理想的物理特性。在这方面，基于极性钙钛矿的过渡金属氧化物可作为界面处的掺杂层，并有望显著调节基于STO的异质结构系统中二维电子气的电子特性。在此，我们使用自旋极化密度泛函理论计算，研究了LaTiO3（LTO）层对LAO/STO异质结构中n型（LaO）(+1)/(TiO2)(0)界面处二维电子气电子特性的掺杂效应。我们的结果表明，费米能级附近的轨道占据增强，其随LTO单胞数量增加，导致二维电子气的电荷载流子密度高于未掺杂系统。电荷载流子密度的增强归因于LTO掺杂单胞中Ti 3d(1)轨道引入的额外电子。这一结论与最近的实验结果一致（《应用物理快报》，2013年，第102卷，091601）。详细的电荷密度和态密度分析表明，LTO掺杂的异质结构系统中的二维电子气主要来自部分占据的dyz和dxz轨道。
