Evidence for indirect band gap in BaSnO3 using angle-resolved photoemission spectroscopy

Abstract

Transparent BaSnO 3 thin films have been proposed as an alternative transparent conducting oxide (TCO). Although bulk synthesis and high-quality fabrication of epitaxial films are well established, there are still unsolved aspects about their electronic structure, such as the direct or indirect nature and the size of the band gap. We investigated the electronic structure of epitaxial BaSnO 3 thin films using in situ angle-resolved photoemission spectroscopy. We directly measured an indirect band gap of 3.7 eV, a value compatible with those of previous reports, but we also identified additional in-gap states at −1.6 eV below the conduction band minimum that we attribute to intrinsic defects, mainly oxygen vacancies.

A consistent picture of excitations in cubic BaSnO$_{3}$ revealed by combining theory and experiment

“…30. Overall, the measured values are also in agreement with most reported experimental values that are about ∼3.0 [31,33] and 3.5 eV [24,29,38] for the onset of the indirect and direct transitions, respectively. Note that both values are not fundamental band gaps as the spectra include excitonic effects.…”

“…While the latter stems from strong direct transitions, we assign the former to originate from indirect transitions. This characteristic is inline with recent experimental observations from optical absorption [30], as well as with angle-resolved photoemission spectroscopy [38]. This finding is also supported by calculations on the independent-particle level [37].…”

“…However, effective masses, band gaps, and absorption edge are still controversial. While, the value of the fundamental gap is under debate, there is evidence of its indirect character, obtained by angle-resolved photoemission spectroscopy [38] and absorption measurements [30]. Measured values [4,[21][22][23][24][25][26][27][28][29][30][31][32][33] for the indirect fundamental gap vary between 2.85 and 3.3 eV, while for the direct counterpart between 3.1 and 4 eV, with a majority of the latter being around 3.5 eV.…”

Controlling surface carrier density by illumination in the transparent conductor La-doped BaSnO3

“…Previous LBSO studies have reported optical gaps between 2.85 and 4.02 eV, [21][22][23][24][25] indicating that the chemical potential in La 0.035 Ba 0.965 SnO 3 has been pushed upwards near the BSO conduction band minimum (CBM) consistent with electron doping and previous ARPES measurements. 26 All samples exhibit a metallic state crossing the Fermi level (E F ) near (k x ,k y ) ¼ (0,0), as shown in Fig. 1…”

In situ investigation of conducting interface formation in LaAlO3/SrTiO3 heterostructure

“…We prepared the high-quality epitaxial LAO films on defect-free 10-UC-thick STO buffer layer covered single crystal Nb-0.5wt%-doped STO (001) using pulsed laser deposition (PLD) [34][35][36] . Note that the conducting STO substrate was used to prevent the charging problem during the ARPES experiments.…”