Near infrared to visible intersubband transitions in all-oxide quantum wells using BaSnO3

Quantum wells (QWs) are made up of a larger bandgap “barrier” material sandwiching the smaller bandgap “well” material. Recently, QW structures using metal oxides such as SrTiO₃ (STO)/LaAlO₃ have been reported. They boast a rather large conduction band offset of ~2.3eV but suffer from STOs large effective mass. On the other hand, BaSnO₃ has a small effective mass(m*_BSO =0.2m_e ) that allows for larger spacing of the QW energy levels. BaSnO₃ also, has very high mobility (150cm^2(Vs)^-1) and a wide bandgap (~3.1eV) making it a great candidate in applications calling for transparent conductive films. We will discuss MBE-grown Al₂O₃/BaSnO₃ quantum wells demonstrating a high level of confinement. However, growing Al₂O₃/BaSnO₃ multi-quantum structure in this materials system has proven to be challenging. We demonstrate that the problem can be resolved using MgO instead of Al₂O₃ as a “barrier” material and BaSnO₃ (BSO) as a “well” material. The metal oxide quantum wells allow intersubband transitions from visible to infrared range enabling many applications.