Experimental evidence of negative quantum capacitance in topological insulator for sub-60-mV/decade steep switching device

As a three-dimensional topological insulator (TI), bismuth telluride (Bi₂Te₃) has two-dimensional electron gas on its surface where negative quantum capacitance (NQC) can exist at a specific biasing condition. In order to experimentally confirm NQC in a TI, a metal-insulator-semiconductor (MIS) capacitor (i.e., metal-Bi₂Te₃-SiO₂-silicon) is fabricated. The capacitance-voltage measurement of the MIS capacitor at 300 K shows that as the depletion capacitance in silicon decreases, the total capacitance of the MIS capacitor, which consists of two capacitors connected in series (i.e., insulator capacitor and depletion capacitor), increases in the depletion region at a frequency of 50 kHz. The amplified capacitance indicates the existence of NQC on the surface of the TI, and it originates from the strongly correlated electron system. The NQC of the TI opens avenues for sub-60-mV/decade steep switching silicon devices.