Effects of vacuum annealing on the electron mobility of epitaxial La-doped BaSnO3 films

Hai Jun Cho,Mian Wei,Hiromichi Ohta,Takaki Onozato,Anup Sanchela

doi:10.1063/1.5054154

Abstract

Wide bandgap (Eg ∼ 3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (∼320 cm2 V−1 s−1) with a high carrier concentration (∼1020 cm−3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we report that the mobility suppression in LBSO films can be lifted by a simple vacuum annealing process. The oxygen vacancies generated from vacuum annealing reduced the thermal stability of LBSO films on MgO substrates, which increased their carrier concentrations and lateral grain sizes at elevated temperatures. As a result, the carrier mobilities were greatly improved, which does not occur after heat treatment in air. We report a factorial design experiment for the vacuum annealing of LBSO films on MgO substrates and discuss the implications of the results. Our findings expand our current knowledge on the point defect formation in epitaxial LBSO films and show that vacuum annealing is a powerful tool for enhancing the mobility values of LBSO films.

Highlights

Scitation.org/journal/apm forming gas at 950 ◦C, which further improved the μ up to 122 cm2 V−1 s−1.18 According to these studies, oxygen vacancies can neutralize the negative charges at threading dislocations19–21 and induce lateral grain growth at elevated temperatures
We found that La-dopants increased the oxygen vacancy vs. lattice oxygen (VO/lattice oxygen peak (LO)) ratio in as-deposited La-doped BaSnO3 (LBSO) films and affected the vacuum annealing effect
According to the thickness dependence, the carrier concentration enhancement was greatly reduced with increasing thickness [Fig. 2(c)] the oxygen vacancy generated from vacuum annealing would have been similar as the La3+ doping levels were the same unless the chemical potential of oxygen depends on the lattice strain

Summary

Introduction

Scitation.org/journal/apm forming gas at 950 ◦C, which further improved the μ up to 122 cm2 V−1 s−1.18 According to these studies, oxygen vacancies can neutralize the negative charges at threading dislocations19–21 and induce lateral grain growth at elevated temperatures. We found that La-dopants increased the oxygen vacancy vs lattice oxygen (VO/LO) ratio in as-deposited LBSO films and affected the vacuum annealing effect.

Results

Conclusion