rf Quantum Capacitance of the Topological Insulator Bi 2 Se 3 in the Bulk Depleted Regime for Field-Effect Transistors

The massless surface states of topological insulators (TIs) are of great interest for tomorrow's electronics. However, excessive defect doping of bulk bands significantly hinders the studies that would enable applications of TIs, in particular as efficient channel materials for high-frequency transistors. The authors take an important step toward resolving this problem, by realizing a Bi${}_{2}$Se${}_{3}$-based capacitive device operating at radio frequencies. Judicious choice of growth technique, substrate, and gate dielectric allow the depletion of bulk carriers and quantitative measurement of the rf quantum capacitance of the topological surface states.