Pulsed-laser deposition of perovskite polar oxide films on SrTiO₃and study of interfacial transport properties

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Pulsed-laser deposition of perovskite polar oxide films on SrTiO₃and study of interfacial transport properties


Author: Li, Danfeng
Title: Pulsed-laser deposition of perovskite polar oxide films on SrTiO₃and study of interfacial transport properties
Degree: M.Phil.
Year: 2011
Subject: Hong Kong Polytechnic University -- Dissertations
Thin films
Pulsed laser deposition
Department: Dept. of Applied Physics
Pages: ix, 97 leaves : ill. (chiefly col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2425059
URI: http://theses.lib.polyu.edu.hk/handle/200/6066
Abstract: Recently, motivated by the discovery of a high-mobility (~10³ cm² V⁻¹ s⁻¹ at 4.2 K) quasi-two dimensional electron gas (q2-DEG) with high carrier density (10¹⁴ cm⁻²) at heterointerfaces combining two band insulators LaAlO₃ (LAO) and SrTiO₃(STO), numerous electronic properties at such interface have been deeply investigated, revealing superconducting and intriguing magneto-transport properties at low temperatures. These significant results show the potential for this oxide interface to be applied in nanoelectronics. However, there is still an ongoing debate concerning the origin of the conducting interface formed between LAO and STO. Since the fundamental mechanism of generating the q2-DEG at perovskite oxide interfaces has always been the main issue of this field, instead of investigating deeply into the physics behind LAO/STO interfaces, it would also be worthy to fabricate other heterointerfaces using another insulating perovskite, which has the same polar atomic planes as LAO, on top of STO. Based on this idea, another "polar" perovskite Dysprosium Scandate (DyScO₃, DSO) was chosen in this project, and the electronic transport properties of the DSO/STO polar heterointerface grown at different oxygen pressures were studied. This heterointerface not only holds some similarities to LAO/STO interface, such as metallic behavior, high mobility and high carrier density, but also presents some phenomena not usually been observed at the LAO/STO interface, such as metal-to-semiconductor (M-S) transition. The electric field effect to the formed electron gas has also been revealed, indicating pronounced modulation of electric doping level and quantum phase transition. This heterostructure promises the potential interest for understanding quasi-two-dimensional electron gases as well as its applications in all-oxide device, thus opens new route to complex oxide physics and ultimately for the design of devices in oxide electronics. In addition, it is generally believed that STO itself plays a vital role in generating q2-DEG at the LAO/STO heterointerfaces. In order to deeply understand the functions of STO and tackle the potential in applications through building LAO/STO conducting interfaces on artificial STO, the LAO/STO (artificial)/STO (single-crystal) structures were also studied. LAO/STO/STO structures were fabricated using pulsed-laser deposition by firstly growing an artificial STO layer on top of STO single crystal and followed by sequential growing of LAO on top. Structural, transport and dielectric measurements have been performed and the importance of STO in such conducting heterointerfaces has been demonstrated. The results show that with artificial STO layer grown at different temperatures the conductivity of LAO/STO heterointerfaces can be very different.

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