Critical role of terminating layer in formation of 2DEG state at the LaInO₃/BaSnO₃ interface

Based on the interface polarization model, the two-dimensional electron gas (2DEG) at LaInO₃(LIO)/BaSnO₃(BSO) interfaces is understood to originate from a polarization discontinuity at the interface and the conduction band offset between LIO and BSO.[1,2] In this scenario, the direction of polarization at the interface is determined by whether the first atomic LIO layer at the interface is LaO⁺ or InO2⁻. We investigate the role of the terminating layer at the LIO/BSO interface in creating the 2DEG. Based on conductance measurements of our in-situ grown LIO/BSO heterostructures, we report in this work that the 2DEG only forms when the BSO surface is terminated mainly with a SnO₂ layer. We controlled the terminating layer by additional SnO₂ deposition on the BSO surface. We show that the as-grown BSO surface has a mixed terminating layer of BaO and SnO₂ while the BSO surfaces prepared with additional SnO₂ deposition are terminated mainly with the SnO₂ layer. The terminating layer was confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS). Our finding is consistent with the interface polarization model for 2DEG formation at LIO/BSO interfaces, in which the direction of the interfacial polarization in LIO is determined by the terminating layer of the BSO surface.[3]

[1] U. Kim et al., APL Mater. 4, 071102 (2016)

[2] Y. M. Kim et al., Sci. rep. 9, 16202 (2019)

[3] S. Kim et al., Adv. Mater. Interfaces 2201781 (2022)