Two sub-band conductivity of Si quantum well

TL;DR

This study investigates two sub-band transport in a silicon quantum well, revealing how sub-band spacing varies with electron density and how conductance features relate to wave function localization and interface disorder.

Contribution

It provides experimental insights into sub-band behavior and conductance features in silicon quantum wells, highlighting the effects of well potential symmetry and interface disorder.

Findings

Sub-band spacing varies from 2.3 to 0.3 meV with electron density.

Conductivity exhibits strong non-monotonic features.

Non-monotonic behavior linked to wave function delocalization and interface disorder.

Abstract

We report on two sub-band transport in double gate SiO$_2$-Si-SiO$_2$ quantum well with 14 nm thick Si layer at 270 mK. At symmetric well potential the experimental sub-band spacing changes monotonically from 2.3 to 0.3 meV when the total density is adjusted by gate voltages between $\sim 0.7\times 10^{16}$ $-3.0\times 10^{16}$ m$^{-2}$. The conductivity is mapped in large gate bias window and it shows strong non-monotonic features. At symmetric well potential and high density these features are addressed to sub-band wave function delocalization in the quantization direction and to different disorder of the top and bottom interfaces of the Si well. Close to bi-layer/second sub-band threshold the non-monotonic behavior is interpreted to arise from scattering from localized band tail electrons.