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

Abstract

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.

Steep-slope transistors enabled with 2D quantum coupling stacks

“…Recently, negative quantum capacitance (NQC) induced by 2D electron gas (2DEG) has been proposed to achieve low SS [24][25][26][27][28][29][30]. NQC was observed in graphene at a strong magnetic field [25].…”

“…Negative electronic compressibility and quantum capacitance can be achieved even without the presence of a magnetic field, by tuning the Fermi energy near the Dirac point [27]. NQC was also observed in topological insulators [28][29][30]. The gate-channel stacks consisting of these quantum materials have strong electron-electron interaction which significantly enhances NQC and leads to small SS [31,32].…”