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Impact of structural modifications on dielectric properties of epitaxial rare-earth oxides on silicon

结构修饰对硅外延稀土氧化物介电性能的影响

基本信息

批准号：
187475991
负责人：
Professor Dr. H. Jörg Osten
金额：
--
依托单位：
Institut für Materialien und Bauelemente der Elektronik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2011
资助国家：
德国
起止时间：
2010-12-31 至 2014-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/187475991?language=en
关键词：
Impact structural modifications dielectric properties

项目摘要

A very promising way to realize advanced future devices is using single-crystalline, closely lattice matched oxides, which will be deposited on the substrate of choice. Binary crystalline rare earth oxides have proved to be a very promising group of dielectrics for epitaxial growth. Under certain conditions, thin rare earth oxide layers epitaxially grown on Si exhibit dielectric constants that are much larger than the known bulk values. The reason for that enhancement effect is not fully understood yet. In the on-going project, we investigate the effect of lattice-mismatch induced strain on dielectric properties. We could show that tetragonal distortion of the cubic lattice is not sufficient to explain the enhancement in K. Therefore, we propose more severe strain induced structural phase deformations into a monoclinic phase. In the prosecution of that project, we will investigate this phase transition in more detail. First results show that Gd2O3 (under tensile stress) and Nd2O3 (under compressive stress) on Si exhibit nearly the same enhancement in the dielectric constant. By growing Nd2O3 on Ge and Si substrates, we will have a model system with identical amount of stress (the lattice mismatch is equal in both cases) but opposite sign (tensile on Ge but compressive on Si). Investigation of the K enhancement for layers with varying thicknesses for both cases should deliver a detailed picture of the stress dependence of this phase transition. Preliminary investigations reveal that Gd2O3 layer growth on Si at low temperatures leads to tetragonal distorted cubic lattices. The temperature was probably not sufficient for a structural phase transition. We expect to understand the dynamics of such a phase transition by growing and evaluating thin Gd2O3 at different temperatures. Complimentary, post-growth anneals of tetragonal distorted layers will be investigated. Our investigations revealed that N doping in epitaxial Gd2O3 thin films can be instrumental in improving their dielectric properties. Substantial reduction of the leakage current density and disappearance of hysteresis in capacitance-voltage characteristics observed in the Gd2O3:N layers indicate that nitrogen incorporation in Gd2O3 effectively eliminates the adverse effects of the oxygen vacancy induced defects in the oxide layer. However, one needs to consider that N incorporation can also dramatically influence the electrical properties of high-K oxides by changing their electronic structures. In order to optimize the electrical properties of the epi-rare earth oxides by means of N doping, it is therefore imperative to investigate the evolution of their electronic structure as a function of N concentration. As an extension to our work on N doped epitaxial Gd2O3 layers we need to investigate the effect of N incorporation on the electronic structure of Gd2O3:N layers which is essential to optimize their electrical properties.

实现先进未来器件的一种非常有希望的方式是使用单晶、紧密晶格匹配的氧化物，这种氧化物将沉积在选定的衬底上。二元晶态稀土氧化物是一类非常有前途的外延生长介质。在某些条件下，在硅上外延生长的薄稀土氧化层的介电常数远远大于已知的体积值。这种增强效应的原因尚不完全清楚。在正在进行的项目中，我们研究了晶格失配引起的应变对介电性能的影响。我们可以证明，立方晶格的四方形变不足以解释K的增强。因此，我们提出了更严重的应变诱导结构相变为单斜相。在该项目的实施过程中，我们将更详细地调查这一阶段转变。第一个结果表明，Gd2O3(在拉应力下)和Nd2O3(在压应力下)在Si上表现出几乎相同的介电常数增加。通过在Ge和Si衬底上生长Nd_2O_3，我们将得到一个应力大小相同(晶格失配在两种情况下都相等)但符号相反(在Ge上拉伸，在Si上压缩)的模型系统。对这两种情况下不同厚度的层的K增强的研究应该提供这种相变的应力依赖的详细图像。初步研究表明，低温下在硅上生长Gd_2O_3层导致了四方晶格的扭曲。温度可能不足以进行结构相变。我们期望通过在不同温度下生长和评估薄Gd2O_3来了解这种相变的动力学。我们将对四方扭曲层的生长后退火进行研究。我们的研究表明，外延Gd2O3薄膜中的N掺杂有助于改善其介电性能。在Gd2O3：N层中观察到的漏电流密度的显著降低和电容-电压特性的滞后消失表明，氮的加入有效地消除了氧化层中氧空位引起的缺陷的不利影响。然而，需要考虑的是，N掺杂也可以通过改变高K氧化物的电子结构来显著影响其电学性质。为了通过N掺杂优化表观稀土氧化物的电学性质，研究其电子结构随N掺杂浓度的变化是非常必要的。作为对N掺杂外延Gd_2O_3层工作的扩展，我们需要研究N掺杂对Gd_2O_3：N层电子结构的影响，这对于优化Gd_2O_3：N层的电学性质至关重要。