Xu Chencheng, Bäumer Christoph, Heinen Ronja Anika, Hoffmann-Eifert Susanne, Gunkel Felix, Dittmann Regina
Peter Grünberg Institute 7, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
Institute of Materials in Electrical Engineering and Information Technology II, RWTH Aachen University, 52074 Aachen, Germany.
Sci Rep. 2016 Mar 24;6:22410. doi: 10.1038/srep22410.
The influence of non-equilibrium and equilibrium processes during growth of LaAlO3/SrTiO3 (LAO/STO) heterostructures is analyzed. We investigate the electronic properties of LAO/STO heterostructures obtained at constant growth conditions after annealing in different oxygen atmospheres within the typical growth window (1 × 10(-4) mbar -1 × 10(-2) mbar). The variation of annealing conditions is found to cause a similar change of electronic properties as observed for samples grown in different oxygen pressure. The results indicate that equilibrium defect formation is the dominant process for establishing the properties of the two-dimensional electron gas (2DEG), while growth dynamics play a minor role in the typical LAO/STO growth regime. Furthermore, the effects of non-equilibrium processes occurring during growth are investigated in detail by quenching just-grown LAO/STO heterostructures directly after growth. We show that during growth the sample is pushed into a non-equilibrium state. After growth, the sample then relaxes towards equilibrium, while the relaxation rate strongly depends on the ambient pressure. The observed relaxation behavior is mainly associated with a reoxidation of the STO bulk, while the 2DEG is formed immediately after the growth.
分析了LaAlO3/SrTiO3（LAO/STO）异质结构生长过程中非平衡和平衡过程的影响。我们研究了在典型生长窗口（1×10^(-4)毫巴 - 1×10^(-2)毫巴）内于不同氧气气氛中退火后，在恒定生长条件下获得的LAO/STO异质结构的电子特性。发现退火条件的变化会导致与在不同氧气压力下生长的样品所观察到的类似的电子特性变化。结果表明，平衡缺陷形成是建立二维电子气（2DEG）特性的主导过程，而生长动力学在典型的LAO/STO生长机制中起次要作用。此外，通过在生长后直接淬灭刚生长的LAO/STO异质结构，详细研究了生长过程中发生的非平衡过程的影响。我们表明，在生长过程中样品被推至非平衡状态。生长后，样品随后向平衡态弛豫，而弛豫速率强烈依赖于环境压力。观察到的弛豫行为主要与STO体的再氧化有关，而2DEG在生长后立即形成。
