von Soosten Merlin, Christensen Dennis V, Eom Chang-Beom, Jespersen Thomas S, Chen Yunzhong, Pryds Nini
Department of Energy Conversion and Storage, Technical University of Denmark, DTU Risø Campus, 4000, Roskilde, Denmark.
Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark.
Sci Rep. 2019 Nov 29;9(1):18005. doi: 10.1038/s41598-019-54463-w.
Heterostructures and crystal interfaces play a major role in state-of-the-art semiconductor devices and play a central role in the field of oxide electronics. In oxides the link between the microscopic properties of the interfaces and bulk properties of the resulting heterostructures challenge our fundamental understanding. Insights on the early growth stage of interfaces and its influence on resulting physical properties are scarce - typically the information is inferred from post growth characterization. Here, we report on real time measurements of the transport properties of SrTiO-based heterostructures at room temperature, while the heterostructure is forming. Surprisingly, we detect a conducting interface already at the initial growth stage, much earlier than the well-established critical thickness limit for observing conductivity ex-situ after sample growth. We investigate how the conductivity depends on various physical processes occurring during pulsed laser depositions, including light illumination, particle bombardment by the plasma plume, interactions with the atmosphere and oxygen migration from SrTiO to the thin films of varying compositions. We conclude that the conductivity in these room-temperature grown interfaces stem from oxygen vacancies with a concentration determined primarily by a balance between vacancy formation through particle bombardment and interfacial redox reaction and vacancy annihilation through oxidation. Using this approach, we propose a new design tool to control the electrical properties of interfaces in real time during their formation.
异质结构和晶体界面在先进半导体器件中起着重要作用，并且在氧化物电子学领域中处于核心地位。在氧化物中，界面的微观性质与所得异质结构的体性质之间的联系对我们的基本理解提出了挑战。关于界面早期生长阶段及其对所得物理性质影响的见解很少——通常这些信息是从生长后的表征中推断出来的。在这里，我们报告了在室温下SrTiO基异质结构形成过程中其输运性质的实时测量。令人惊讶的是，我们在初始生长阶段就检测到了一个导电界面，这比样品生长后非原位观察到导电性所确立的临界厚度极限要早得多。我们研究了电导率如何取决于脉冲激光沉积过程中发生的各种物理过程，包括光照、等离子体羽流的粒子轰击、与大气的相互作用以及氧从SrTiO向不同成分薄膜的迁移。我们得出结论，这些室温生长界面中的电导率源于氧空位，其浓度主要由粒子轰击和界面氧化还原反应导致的空位形成与氧化导致的空位湮灭之间的平衡决定。利用这种方法，我们提出了一种新的设计工具，用于在界面形成过程中实时控制其电学性质。
