La-doped BaSnO₃ (BLSO) is a wide bandgap semiconducting perovskite oxide with high electron mobility and excellent oxygen stability at room temperature [1]. In recent reports on the excellent carrier modulation of BLSO channel by field effect on perovskite SrTiO₃ (STO) [2] and non-perovskite MgO substrates [3], we found an optimized thickness for undoped BaSnO₃ (BSO) buffer layer to be around 150 nm. However, BSO shows persistent and large photoconductivity under the light with wavelength smaller than 400 nm.
To prevent the change of channel conductance by such photoconductivity of the BSO buffer layer, we fabricated an atomically-mixed Ba_xSr_1-xHfO₃ (BSHO) buffer layer. Both BaHfO₃ (BHO) and SrHfO₃ (SHO) have wider bandgaps than BSO (5.8 eV and 6.1 eV respectively) and show no measurable photoconductivity. Also, BHO is a high-k dielectric material with a dielectric constant of 38. We reduced BSHO lattice mismatch with BLSO by finding a suitable ratio of BHO to SHO. We will report on the field effect transistor performances with BSHO as a buffer layer on BLSO channel layer as well as a gate dielectric.

[1] H. J. Kim, U. Kim et al., Appl. Phys. Express 5, 061102 (2012).
[2] U. Kim et al., APL Mater. 4, 071102 (2016).
[3] Juyeon Shin et al., Appl. Phys. Lett. 109, 262102 (2016).