Josephson Field Effect Transistors with InAs on Insulator and High Permittivity Gate Dielectrics

Abstract

InAs on Insulator (InAsOI) has been recently demonstrated as a promising platform to develop hybrid semiconducting-superconducting Josephson Junctions (JJs) and Josephson field effect transistors (JoFETs). The InAsOI consists of an InAs epilayer grown onto a cryogenic-electrically insulating InAlAs metamorphic buffer, which allows the electrical decoupling of surface-exposed adjacent devices together with a high critical current density integration. The miniaturization of Si microchips has progressed significantly due to the integration of high permittivity (high-k) gate insulators, allowing an increased gate coupling with the transistor channel with consequent reduced gate operating voltages and leakages. As well as for Si-based FETs, integrating high-k gate insulators with JoFETs promises similar advantages in superconducting electronics. Here, we investigate the gate-tunable electrical properties of InAsOI-based JoFETs featuring different high-k gate insulators, namely, HfO₂ and Al₂O₃. We found that both the ungated and gate-tunable electrical properties of JoFETs are strongly dependent on the insulator chosen. With both dielectrics, the JoFETs can entirely suppress the switching current and increase the normal-state resistance by 10–20 times using negative gate voltages. The HfO₂-JoFETs exhibit improved gate-tunable electrical performance compared to those achieved with Al₂O₃-JoFETs, which is related to the higher permittivity of the insulator. Gate-dependent electrical properties of InAsOI-based JoFETs were evaluated in the temperature range from 50 mK to 1 K. As expected, the switching current monotonically decreases with the increase in temperature, while the normal-state resistance remains unchanged until 1 K. Moreover, under the influence of an out-of-plane magnetic field, JoFETs exhibited an unconventional Fraunhofer diffraction pattern, from which an edge-peaked supercurrent density distribution was calculated. The origin of such anomalies is identified in the physics of the JJ edges, either with an increased current density or with a more accurate consideration of nonuniform flux focusing on the superconducting leads.