Abstract
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 SrTiO3-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 SrTiO3 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.
Highlights
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
Pulsed laser deposition (PLD) remains the most popular deposition technique for growing STO-based heterostructures, but during this complex deposition process, STO is exposed to all the aforementioned stimuli
We expect that the combination of in-situ methods such as Reflection high-energy electron diffraction (RHEED) and conductivity measurements during growth will give access to a territory where the initial growth conditions can be studied and controlled in detail, leading to new and improved properties of the interface
Summary
Amorphous LaAlO3, amorphous LaSr1/8Mn7/8O3 and crystalline γ-Al2O3 layers were grown by PLD at an oxygen pressure of 2 × 10−6 mbar at room temperature, consistent with previous studies[2,9,35]. The electrical resistance of the interfaces was measured during the deposition process by means of a sample carrier constructed and placed inside the PLD chamber. Measurements were performed using a 4-probe method in the Van der Pauw geometry, except for Fig. 4b where the consistency between Hall-bar and Van der Pauw samples were studied. The sheet resistance was extracted by linear fits to voltage biased I-V www.nature.com/scientificreports measurements with a maximum current of 50 nA and a repetition rate of 5 I/V traces per second. Hall-bar samples were prepared by UV-lithography, and PLD deposition was performed on the exposed and developed patterns[33]. The conductivity was found to be invariant to whether the pressure gauge was turned on or off[19] and whether the electron beam from the RHEED (20 kV, 1.55 A) irradiated the sample surface
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