Tunability of the Electronic Properties of Epitaxial Bi (111) Films Using Printable Ion-gel Gating

Elemental bismuth (Bi) semimetal thin films exhibit novel spin- and charge-transport properties that arise from their high mobility Rashba spin-split surface states. However, there has been limited progress on modulation of these properties through extrinsic control such as electric field-effect. Here, we report the tunability of the electronic properties of epitaxial Bi (111) films grown on GaAs by electron double-layer gating using a hexagonal boron nitride (hBN) based ion-gel. In contrast to conventional ionic liquids, solid-state hBN ion-gel allows facile patterning on the top of prepatterned Bi Hall bars by aerosol jet printing. Magneto-transport measurements demonstrate that the application of small gate voltages (ranging from +0.4V to -0.4V) through hBN ion-gel induces significant modulation in charge carrier density and mobility of Bi thin films, leading to a pronounced response in the Hall conductivity. By varying gate voltage, we can identify electron- or hole-dominated transport in Bi films of different thicknesses. For example, 10-nm-thick Bi film shows holes dominated Hall conductivity, whereas 30-nm-thick film shows the presence of both electron and hole pockets. Thus, our work highlights the potential of a novel hBN-based solid-state ion-gel gating as a versatile materials system to engineer the electronic properties of topological materials, paving the way for future applications in advanced electronic devices.