Unusually large enhancement of thermopower in an electric field induced two-dimensional electron gas

TL;DR

This study demonstrates a significant enhancement of thermopower in an electric field induced two-dimensional electron gas on SrTiO3, surpassing bulk values and opening new avenues for thermoelectric materials.

Contribution

It reports the first observation of unusually large thermopower enhancement in an electric field induced 2DEG, using a novel gate insulator and precise carrier confinement.

Findings

Thermopower |S| increased from ~600 to ~950 μV/K at high carrier concentration.

Electric field induced 2DEG achieved carrier densities up to ~2E15 /cm^2.

Enhanced thermopower was approximately five times larger than bulk values.

Abstract

Two-dimensionally confined electrons showing unusually large thermopower (S) have attracted attention as a potential approach for developing high performance thermoelectric materials. However, enhanced S has never been observed in electric field induced two-dimensional electron gas (2DEG). Here we demonstrate electric field modulation of S for a field effect transistor (FET) fabricated on a SrTiO3 crystal using a water-infiltrated nanoporous glass as the gate insulator. An electric field application confined carrier electrons up to ~2E15 /cm^2 in an extremely thin (~2 nm) 2DEG. Unusually large enhancement of |S| was observed when the sheet carrier concentration exceeded 2.5E14 /cm^2, and it modulated from ~600 (~2E15 /cm^2) to ~950 {\mu}V/K (~8E14 /cm^2), which were approximately five times larger than those of the bulk, clearly demonstrating that an electric field induced 2DEG provides unusually large enhancement of |S|.