Robust topological surface states of Bi2Se3 thin films on amorphous SiO2/Si substrate and a large ambipolar gating effect

TL;DR

This study demonstrates that Bi2Se3 topological insulator thin films grown on amorphous SiO2/Si substrates retain robust surface states and exhibit significant gating effects, highlighting the importance of chemical compatibility over lattice matching for growth.

Contribution

It shows that topological surface states are robust on amorphous substrates and that chemical compatibility is more crucial than lattice matching for TI film growth.

Findings

Topological surface states observed on Bi2Se3 films on amorphous SiO2.

Films on amorphous substrates show superior transport properties despite in-plane randomness.

Large ambipolar gating effect achieved using doped-Si back gate.

Abstract

The recent emergence of topological insulators (TI) has spurred intensive efforts to grow TI thin films on various substrates. However, little is known about how robust the topological surface states (TSS) are against disorders and other detrimental effects originating from the substrates. Here, we report observation of a well-defined TSS on Bi2Se3 films grown on amorphous SiO2 (a-SiO2) substrates and a large gating effect on these films using the underneath doped-Si substrate as the back gate. The films on a-SiO2 were composed of c-axis ordered but random in-plane domains. However, despite the in-plane randomness induced by the amorphous substrate, the transport properties of these films were superior to those of similar films grown on single-crystalline Si(111) substrates, which are structurally better matched but chemically reactive with the films. This work sheds light on the importance of chemical compatibility, compared to lattice matching, for the growth of TI thin films, and also demonstrates that the technologically-important and gatable a-SiO2/Si substrate is a promising platform for TI films.