Our recent work on rf-capacitor devices made out of layered hexagonal-boron nitride (hBN) and Bi2Se3 stacks was recently published in Physical Review Applied .
This work probes the rf-response of surface Dirac electrons in Bi2Se3 obtained by CVD-growth on hBN. It is the first investigation that addresses this issue, that is of capital importance to the future use of topological insulators in high-mobility transistors and GHz devices. One of key hurdles that scientists are confronted with in topological insulators is their native defects, that creates free mobiles electrons. Our device essentially operates as a gate-channel stack, where the gate is use to simultaneously deplete free charge carriers and probe the quantum capacitance of the system. The quantum capacitance is related to the electronic compressibility or the density of states of the system. We succeed in observing the Dirac point in Bi2Se3 via capacitance measurements performed at GHz frequencies. Although several obstacles remain to be overcome before topological materials can be implemented as transistors channels, our work achieves a two-fold result: (i) our devices employs a new combination of mechanical exfoliation and CVD growth to realize a hBN-Bi2Se3-hBN sandwich structure. (ii) we observe the Dirac response of surface states at GHz frequencies.
Bi2Se3/hBN stack embedded in RF waveguide.