Effect of Oxygen Partial Pressure on Crystal Structure, Oxygen Vacancy, and Surface Morphology of Epitaxial SrTiO3 Thin Films Grown by Ion Beam Sputter Deposition

Gasidit Panomsuwan,Nagahiro Saito

doi:10.3390/oxygen1010007

Abstract

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates at 800 °C by an ion beam sputter deposition (IBSD). Oxygen partial pressure (PO2) was varied at 1.5 × 10−5, 1.5 × 10−4, and 1.5 × 10−3 Torr during the growth. The effects of PO2 on crystal structure, oxygen vacancy, and surface morphology of the STO films were investigated and are discussed to understand their correlation. It was found that PO2 played a significant role in influencing the crystal structure, oxygen vacancy, and surface morphology of the STO films. All STO films grew on the LAO substrates under a compressive strain along an in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). The crystalline quality of STO films was slightly improved at higher PO2. Oxygen vacancy was favorably created in the STO lattice grown at low PO2 due to a lack of oxygen during growth and became suppressed at high PO2. The existence of oxygen vacancy could result in a lattice expansion in both out-of-plane and in-plane directions due to the presence of Ti3+ instead of Ti4+ ions. The surface roughness of the STO films gradually decreased and was nearly close to that of the bare LAO substrate at high PO2, indicating a two-dimensional (2D) growth mode. The results presented in this work provide a correlation among crystal structure, oxygen vacancy, and surface morphology of the epitaxial STO films grown by IBSD, which form a useful guideline for further study.

Highlights

Epitaxial strontium titanate (SrTiO3, STO) thin films have drawn considerable attention as an essential component in various electronic devices, including capacitors [1], tunable phase shifters [2], sensors [3], non-volatile memory [4], memristors [5], and electromechanical actuators [6], owing to their high dielectric constant, low loss, large dielectric tunability, and tunable optical properties
The results presented in this work provide a correlation among crystal structure, oxygen vacancy, and surface morphology of the epitaxial STO films grown by ion beam sputter deposition (IBSD), which form a useful guideline for further study
Epitaxial STO films have been successfully grown on various types of substrates by a variety of methods, such as pulsed laser deposition (PLD) [7,8], molecular beam epitaxy (MBE) [9,10], metal-oxide chemical vapor deposition (MOCVD) [11,12], radio-frequency (RF) magnetron sputtering [13,14], and ion beam sputter deposition (IBSD) [15,16,17]

Summary

Introduction

Epitaxial strontium titanate (SrTiO3 , STO) thin films have drawn considerable attention as an essential component in various electronic devices, including capacitors [1], tunable phase shifters [2], sensors [3], non-volatile memory [4], memristors [5], and electromechanical actuators [6], owing to their high dielectric constant, low loss, large dielectric tunability, and tunable optical properties. Epitaxial STO films have been successfully grown on various types of substrates by a variety of methods, such as pulsed laser deposition (PLD) [7,8], molecular beam epitaxy (MBE) [9,10], metal-oxide chemical vapor deposition (MOCVD) [11,12], radio-frequency (RF) magnetron sputtering [13,14], and ion beam sputter deposition (IBSD) [15,16,17] All methods have their own advantages and disadvantages, so the selection of a growth method depends on which aspect is focused on. For the aspect of the manufacturing process, the IBSD is a viable alternative method to the conventional RF sputtering since it offers several

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Conclusion