Structure and band gap energy of CaSnO3 epitaxial films on LaAlO3 substrate

In this paper we report the epitaxial CaSnO3(CSO) thin films grown on LaAlO3(001) single crystal substrates with thickness ranged from 34 nm to 268 nm by pulsed laser deposition. The microstructures of the films were investigated by high-resolution X-ray diffraction, including conventional θ-2θ linear scans and reciprocal space mappings (RSMs). The thickness dependent strain states and lattice distortion of CSO films were characterized by the in-plane and out-of-plane lattice parameters that were extracted from the symmetry and asymmetry RSMs. The optical properties of CSO films were investigated by measuring the optical transmittances. The band gaps increase gradually from 4.95 eV to 5.38 eV with the film thickness decreasing, which was attributed mainly to the quantum-size effect. The band structure was also investigated theoretically using density-functional theory. The results show that CSO is an indirect band gap semiconductor with the band gap of 3.0 eV. Such a transparent wide band gap semiconductor should be of high interest in epitaxial heterojunction and optical device application.