Mass enhancement of two-dimensional electrons in thin-oxide Si-MOSFET's

TL;DR

This study investigates the effective mass of two-dimensional electrons in thin-oxide Si-MOSFETs, revealing significant mass enhancement influenced by electron interactions and gate charges, with implications for understanding electron behavior in semiconductor devices.

Contribution

It provides a quantitative analysis of effective mass enhancement in thin-oxide Si-MOSFETs and highlights the role of electron-electron interactions and gate charges in this phenomenon.

Findings

Effective mass is enhanced even when oxide thickness is below electron-electron separation.

Mass enhancement can be described by a specific linear relation involving oxide thickness.

The effective g-factor in thin-oxide samples is approximately 3.0.

Abstract

We wish to report in this paper a study of the effective mass (m^*) in thin-oxide Si-metal-oxide-semiconductor field-effect-transistors, using the temperature dependence of the Shubnikov-de Haas (SdH) effect and following the methodology developed by J.L. Smith and P.J. Stiles, Phys. Rev. Lett. {\bf 29}, 102 (1972). We find that in the thin oxide limit, when the oxide thickness $d_{ox}$ is smaller than the average two-dimensional electron-electron separation r, m^* is still enhanced and the enhancement can be described by $m^*/m_B = 0.815 + 0.23(r/d_{ox})$, where $m_B = 0.195 m_e$ is the bulk electron mass, $m_e$ the free electron mass. At $n_s = 6 \times 10^{11}/cm^2$, for example, $m^* \simeq 0.25 m_e$, an enhancement doubles that previously reported by Smith and Stiles. Our result shows that the interaction between electrons in the semiconductor and the neutralizing positive charges on the metallic gate electrode is important for mass enhancement. We also studied the magnetic-field orientation dependence of the SdH effect and deduced a value of $3.0 \pm 0.5$ for the effective $g$ factor in our thin oxide samples.