Selective chemical etching for termination layer control of BaSnO3 and 2DEG formation at the LaInO3/BaSnO3 interface

An ex situ chemical etching method was developed to achieve a SnO2-terminated surface in BaSnO3 films. An SnO2-terminated surface is crucial for the formation of a (LaO)(+)/(SnO2)(0) interface structure to form the two-dimensional electron gas (2DEG) state at the LaInO3 (LIO)/BaSnO3 (BSO) interface. By employing a 9:1 mixture of acetone and water, the etching rate of the surface barium oxide (BaO) layer could be effectively controlled, taking advantage of the solubility of BaO in water. To determine the optimal etching conditions, we investigated the relationship between the etching time and the resulting 2DEG conductance. The optimum times for maximizing the conductance of the 2DEG state were found to be 90 s on SrTiO3 substrates and 40 s on MgO substrates, generating a higher conductance than the in situ SnO2 dusting method reported earlier. The surface properties before and after the chemical etching were analyzed by angle reserved x-ray photoelectron spectroscopy.