Au-gated SrTiO3 field-effect transistors with large electron concentration and current modulation

We report the fabrication of low-leakage rectifying Pt and Au Schottky diodes and Au-gated metal-semiconductor field effect transistors (MESFETs) on n-type SrTiO₃ thin films grown by hybrid molecular beam epitaxy. In agreement with previous studies, we find that compared to Pt, Au provides a higher Schottky barrier height with SrTiO₃. As a result of the large dielectric constant of SrTiO₃ and the large Schottky barrier height of Au, the Au-gated MESFETs are able to modulate ∼1.6 × 10¹⁴ cm^-2 electron density, the highest modulation yet achieved using metal gates in any material system. These MESFETs modulate current densities up to ∼68 mA/mm, ∼20× times larger than the best demonstrated SrTiO₃ MESFETs. We also discuss the roles of the interfacial layer, and the field-dependent dielectric constant of SrTiO₃ in increasing the pinch off voltage of the MESFET.