Cost-effective transparent conductive oxide (TCO) material composed of cheap and abundant elements is highly desired in nowadays optoelectronics. Recently a wide-bandgap La-doped barium stannate (LBSO) n-type semiconductor has been discovered. LBSO single crystal conductive properties rival those of Sn-doped In2O3 (ITO)1. Additionally, BaSnO3 is of perovskite type lattice which allowing this material to be incorporated in various heterostructures as a lattice-matched electrode2. Although, achieving desirable thin film properties for optoelectronic applications is still challenging due to nonstoichiometry and various defects as well as substrate-films interaction – understanding of these factors is crucial for BSO applications. Therefore, in this work thin undoped BaSnO3 films have been deposited using pulsed injection metal organic chemical vapor deposition (PI-MOCVD) method allowing easier compositional control and simultaneous deposition on multiple substrates. In order to achieve low and high film/substrate lattice mismatch, pseudocubic LaAlO3, SrTiO3 and hexagonal Al2O3 substrates were selected respectively. Sn(thd)2 and Ba(thd)2 precursor solution with various ratios in dimethoxyethane was used for thin film deposition. Depositions were carried out in Ar:O2 (8:2 v/v) atmosphere. Layer composition was determined using ICP-MS and Energy Dispersive X-ray (EDX) spectroscopy techniques. Surface morphology and film structure were characterized using Scanning Electron Microscopy (SEM) and X-ray diffractometry. Optical properties were investigated using variable angle spectroscopic ellipsometry and UV-Vis spectrophotometry in transmission mode.
Thin BSO films deposited on (100) LaAlO3, (100) SrTiO3 substrates were highly epitaxial. While polycrystalline films were obtained on Sapphire C substrate. It was determined that a surplus amount of Ba(thd)2 is required to produce stoichiometric films. Interestingly, slight deviation form stoichiometric ratio resulted in significant structural and optical changes while a cubic symmetry was maintained. Also, no additional phases were detected even with a drastic increase of Ba/Sn ratio. Strong lattice parameter correlation with the Ba/Sn ratio in the films suggests a defect-forming mechanism related to oxygen, barium atom vacancies and (BaO)2 Ruddlesden-Popper crystallographic shear faults.