Improvement of electron mobility in La:BaSnO3 thin films by insertion of an atomically flat insulating (Sr,Ba)SnO3 buffer layer

Junichi Shiogai,Atsushi Tsukazaki,Kazuki Nishihara,Kazuhisa Sato

doi:10.1063/1.4953808

Junichi Shiogai, Atsushi Tsukazaki + Show 2 more

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https://doi.org/10.1063/1.4953808

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Abstract

One perovskite oxide, ASnO3 (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO3 substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO3 / (Sr,Ba)SnO3 for buffering this large lattice mismatch between La:BaSnO3 and SrTiO3 substrate. The insertion of 200-nm-thick BaSnO3 on (Sr,Ba)SnO3 bilayer buffer structures reduces the number of dislocations and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO3 buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO3 shows that the highest obtained value of mobility is 78 cm2V−1s−1 because of its fewer dislocations. High electron mobility films based on perovskite BaSnO3 can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

Highlights

Exploration of transparent conductive films (TCFs) possessing high electrical conductivity and a wide band gap higher than 3 eV, has been studied intensively for numerous fundamental applications such as electrodes for optical devices and interconnections of flat panel displays, solar cells, and light-emitting diodes.[1,2] The criteria for TCFs generally include resistivity of less than 10−3Ωcm and transparency higher than 80% in the visible light region
The electron mobility of films grown on SrTiO3 substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch
This study investigates the effect of insertion of bilayer BaSnO3 / (Sr,Ba)SnO3 for buffering this large lattice mismatch between La-doped BaSnO3 (La):BaSnO3 and SrTiO3 substrate

Summary

INTRODUCTION

Exploration of transparent conductive films (TCFs) possessing high electrical conductivity and a wide band gap higher than 3 eV, has been studied intensively for numerous fundamental applications such as electrodes for optical devices and interconnections of flat panel displays, solar cells, and light-emitting diodes.[1,2] The criteria for TCFs generally include resistivity of less than 10−3Ωcm and transparency higher than 80% in the visible light region. A degree of success has been achieved with transparent conductive oxide (TCO) films.[2] TCOs with high charge carrier density have been demonstrated for Sn:In2O3 (ITO),[3] ZnO,[4] SnO2,5 TiO2,6 and their compounds.[7] Among them, the ITO is an exemplary TCO with long stability: it has already been applied for practical use with 10−4 Ω cm. For actual application of perovskite stannates as a transparent semiconductor, many attempts have been undertaken to increase the mobility of La-doped BaSnO3 films by tuning the stoichiometry of Ba/Sn and oxygen and by minimizing the unintentional impurity concentration in films using oxide molecular beam epitaxy.[15] Optimization of growth conditions for the films on SrTiO3 substrates[16] and selecting proper substrates such as PrScO3, SmScO3, BaSnO3, and TbScO315,17–20 have been investigated to reduce the number of threading dislocations. The effect of buffer layer has been validated properly for ferroelectrics,[22] semiconductors,[23,24,25] and cuprate superconducting films.[26]

EXPERIMENTAL PROCEDURE

RESULTS AND DISCUSSIONS

CONCLUSION