Tuning of the Optoelectronic Properties for Transparent Oxide Semiconductor ASnO₃ by Modulating the Size of A-Ions

Recently, La-doped ASnO3 (A = Ba, Sr, and Ca) films have attracted increasing attention as an active channel of deep-ultraviolet transparent thin-film transistors, owing to their wide band gap and high electrical conductivity. However, the effect of A-site substitution on the optoelectronic properties of ASnO3 has not been clarified in a detailed systematic study. Here, we show that the optoelectronic properties of ASnO3 can be tuned systematically by changing the average size of the A-site ion. We heteroepitaxially fabricated ASnO3 films on (001) LaAlO3 substrates and measured their optical absorption spectra and electron transport properties. The lattice parameter almost linearly increased from 3.95 to 4.14 Å with increasing ionic radius of the A-site ion from 1.34 (Ca2+) to 1.61 Å (Ba2+), whereas the optical band gap gradually decreased from ∼4.6 to ∼3.6 eV with a small positive bowing. With increasing the lattice parameter, the electrical conductivity gradually increased from ∼100 to ∼103 S cm–1 because of gradual increases in both the carrier concentration and mobility. The present results are of significant importance for designing ASnO3-based transparent electronic devices.