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首页> 外文期刊>Physical Review X >Origin of the Two-Dimensional Electron Gas at class='aps-inline-formula'>LaAlO3/SrTiO3 Interfaces: The Role of Oxygen Vacancies and Electroni
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Origin of the Two-Dimensional Electron Gas at class='aps-inline-formula'>LaAlO3/SrTiO3 Interfaces: The Role of Oxygen Vacancies and Electroni

机译：class =“ aps-inline-formula”> LaAlO 3 处的二维电子气的起源msub> / SrTiO 3 界面：氧空位和电子的作用

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The relative importance of atomic defects and electron transfer in explaining conductivity at the crystalline LaAlO3/SrTiO3 interface has been a topic of debate. Metallic interfaces with similar electronic properties produced by amorphous oxide overlayers on SrTiO3 [Y. Chen et al., Nano Lett. 11, 3774 (2011); S.?W. Lee et al., Nano Lett. 12, 4775 (2012)] have called in question the original polarization catastrophe model [N. Nakagawa et al., Nature Mater. 5, 204 (2006)]. We resolve the issue by a comprehensive comparison of (100)-oriented SrTiO3 substrates with crystalline and amorphous overlayers of LaAlO3 of different thicknesses prepared under different oxygen pressures. For both types of overlayers, there is a critical thickness for the appearance of conductivity, but its value is always 4?unit cells (around 1.6?nm) for the oxygen-annealed crystalline case, whereas in the amorphous case, the critical thickness could be varied in the range 0.5 to 6?nm according to the deposition conditions. Subsequent ion milling of the overlayer restores the insulating state for the oxygen-annealed crystalline heterostructures but not for the amorphous ones. Oxygen post-annealing removes the oxygen vacancies, and the interfaces become insulating in the amorphous case. However, the interfaces with a crystalline overlayer remain conducting with reduced carrier density. These results demonstrate that oxygen vacancies are the dominant source of mobile carriers when the LaAlO3 overlayer is amorphous, while both oxygen vacancies and polarization catastrophe contribute to the interface conductivity in unannealed crystalline LaAlO3/SrTiO3 heterostructures, and the polarization catastrophe alone accounts for the conductivity in oxygen-annealed crystalline LaAlO3/SrTiO3 heterostructures. Furthermore, we find that the crystallinity of the LaAlO3 layer is crucial for the polarization catastrophe mechanism in the case of crystalline LaAlO3 overlayers.
机译：在解释晶体LaAlO3 / SrTiO3界面的电导率时，原子缺陷和电子转移的相对重要性一直是争论的话题。由SrTiO3上的非晶氧化物覆盖层产生的具有类似电子特性的金属界面[Y. Chen等，Nano Lett。 11，3774（2011）; S.?W。 Lee等，Nano Lett。 [12，4775（2012）]曾质疑原始的极化灾难模型[N. Nakagawa等，Nature Mater。 5，204（2006）]。我们通过将（100）取向的SrTiO3衬底与在不同的氧气压力下制备的厚度不同的LaAlO3的晶体和非晶态覆盖层进行全面比较，解决了该问题。对于两种类型的叠层，导电性的外观都有一个临界厚度，但对于氧退火的结晶情况，其值始终为4？单位晶胞（约1.6？nm），而在非晶态情况下，临界厚度可以可以根据沉积条件在0.5-6nm范围内变化。随后的覆盖层的离子铣削恢复了氧退火的晶体异质结构的绝缘状态，但不恢复了非晶态的绝缘状态。氧气后退火去除了氧空位，在非晶态情况下界面变得绝缘。但是，具有晶体覆盖层的界面仍保持较低的载流子密度导电。这些结果表明，当LaAlO3覆盖层为无定形时，氧空位是移动载流子的主要来源，而氧空位和极化突变均对未退火的晶体LaAlO3 / SrTiO3异质结构中的界面电导有贡献，而极化空变仅占了氧退火的晶体LaAlO3 / SrTiO3异质结构。此外，我们发现在晶体LaAlO3叠层的情况下，LaAlO3层的结晶度对于极化突变机理至关重要。

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