Structure and optical band gaps of (Ba,Sr)SnO3 films grown by molecular beam epitaxy

Abstract

Epitaxial growth of (BaxSr1−x)SnO3 films with 0 ≤ x ≤ 1 using molecular beam epitaxy is reported. It is shown that SrSnO3 films can be grown coherently strained on closely lattice and symmetry matched PrScO3 substrates. The evolution of the optical band gap as a function of composition is determined by spectroscopic ellipsometry. The direct band gap monotonously decreases with x from to 4.46 eV (x = 0) to 3.36 eV (x = 1). A large Burnstein-Moss shift is observed with La-doping of BaSnO3 films. The shift corresponds approximately to the increase in Fermi level and is consistent with the low conduction band mass.

Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

“…On the other hand, the tensile strained SSO film grown on BLSO/NSTO with ΔV pc  = +1.7% has a direct gap of E g  = 4.31 ± 0.1 eV resulting in a significant band gap change of ΔE g  = 0.6 eV ± 0.2 eV and a band gap change per % unit cell volume change of −0.13 eV/%ΔV pc. Extrapolating ΔV pc to zero yields a direct band gap of 4.4 eV for the SSO film which is close to that reported for predominantly unstrained SSO thin films grown by MBE18. For the compressively (coherently) strained CSO film grown on NSTO the direct band gap is 4.91 ± 0.1 eV which is reduced to 4.64 ± 0.1 eV resulting in a gap change per % unit cell volume change of −0.12 eV/%ΔV pc which is close to the case of the SSO thin film.…”

“…2(a,e) reveal a NSTO ≈ a SSO for the in-plane lattice parameters. Thicker (78 nm) SSO films grown on NSTO were predominantly strain relaxed with a calculated18 unstrained film lattice parameter of 4.03(5) ± 0.05 Å which is close to that of bulk SSO and SSO thin films grown by molecular beam epitaxy (MBE)18. As demonstrated in Fig.…”

“…3. The predominantly relaxed BLSO film with a Hall carrier density of 2.9 × 10 20  cm −3 has a direct gap of 3.87 ± 0.1 eV, comparable to that of MBE grown BLSO films for similar carrier densities18.…”

“…Owing to the comparatively lower indirect band gap absorption expected in stannate thin films as discussed in ref. 18, only the direct band gap Tauc plots are presented in Fig. 3.…”

STEM beam channeling in BaSnO3/LaAlO3 perovskite bilayers and visualization of 2D misfit dislocation network

“…1. While these MDs have been observed in cross-sectional TEM and STEM images [14,[26][27][28], STEM-based plan-view characterization of these interfacial MD networks are lacking [18,19]. This study provides an initial step in STEM characterization of these MD networks.…”