Field-effect mobility enhanced by tuning the Fermi level into the band gap of Bi2Se3

TL;DR

This study demonstrates that tuning the Fermi level into the band gap of calcium-doped Bi2Se3 nanodevices significantly enhances field-effect mobility, indicating suppressed backscattering in topological insulator surface states.

Contribution

It introduces a fabrication-free method to control Fermi level in Bi2Se3 nanodevices, leading to mobility enhancement by tuning into the band gap.

Findings

Mobility increased by over tenfold when Fermi level is in the band gap.

Bulk insulating state preserved in suspended nanodevices.

Fermi level tuning achieved via electron beam irradiation and electrostatic gating.

Abstract

By eliminating normal fabrication processes, we preserve the bulk insulating state of calcium-doped Bi2Se3 single crystals in suspended nanodevices, as indicated by the activated temperature dependence of the resistivity at low temperatures. We perform low-energy electron beam irradiation (<16 keV) and electrostatic gating to control the carrier density and therefore the Fermi level position in the nanodevices. In slightly p-doped Bi2-xCaxSe3 devices, continuous tuning of the Fermi level from the bulk valence band to the band-gap reveals dramatic enhancement (> a factor of 10) in the field-effect mobility, which suggests suppressed backscattering expected for the Dirac fermion surface states in the gap of topological insulators.