Growth Challenges and Future Applications for High Mobility 2DEGs*

Two-dimensional electron gases in complex oxide interfaces offer great promise for high-speed electronics. BaSnO₃ (BSO) is well known for its high mobility due to an availability of unoccupied 5s bands in Sn. SrNbO₃ (SNO) is a 4d transition metal oxide serving as a good donor material in oxide interface. Synthesis is challenging, however, due to the metastable nature of the d¹ Nb⁴⁺ cation and the challenges of delivery of refractory Nb. To that end, SNO thin films were grown using hybrid MBE (hMBE) for the first time using a TDTBN precursor for Nb and an elemental Sr source on GdScO₃ and as prepared BaSnO₃ films on different substrates. Varying thicknesses of SrHfO₃ (SHO) capping layers were deposited using a precursor for Hf on top of SNO films to preserve the metastable surface. Grown films were transferred in vacuo for XPS to quantify elemental composition and Nb oxidation state. Ex situ studies by XANES illustrates the SHO capping plays vital role in preserving the Nb 4d¹ metastable charge state in atmospheric conditions. These studies help to understand the high-quality SNO film growth by hMBE approach and quantify the carrier concentration and mobility in SNO/BSO interface opening the door for promising alternatives for traditional semiconductor in high mobility devices.