Full energy spectra of interface state densities for n- and p-type MoS2 field-effect transistors

TL;DR

This study systematically characterizes the full energy spectra of interface state densities in n- and p-type MoS2 FETs, revealing the effects of different gate structures and the origins of interface degradation.

Contribution

It provides comprehensive energy spectra of interface states for MoS2 FETs, identifying strain and sulfur vacancies as key degradation factors, which is novel in the detailed analysis across various structures.

Findings

Significant reduction of Dit in n-MoS2 with h-BN heterostructure.

High Dit levels persist in p-MoS2 regardless of structure.

Strain and sulfur vacancies are primary causes of interface degradation.

Abstract

Two-dimensional (2D) layered materials are promising for replacing Si to overcome the scaling limit of recent ~5 nm-length metal-oxide-semiconductor field-effect transistors (MOSFETs). However, the insulator/2D channel interface severely degrades the performance of 2D-based MOSFETs, and the origin of the degradation remains largely unexplored. Here, we present the full energy spectra of the interface state densities (Dit) for both n- and p- MoS2 FETs, based on the comprehensive and systematic studies, i.e., thickness range from monolayer to bulk and various gate stack structures including 2D heterostructure with h-BN as well as typical high-k top-gate structure. For n-MoS2, Dit around the mid gap is drastically reduced to 5*10^11 cm-2eV-1 for the heterostructure FET with h-BN from 5*10^12 cm-2eV-1 for the high-k top-gate MoS2 FET. On the other hand, Dit remains high, ~10^13 cm-2eV-1, even for the heterostructure FET for p-MoS2. The systematic study elucidates that the strain induced externally through the substrate surface roughness and high-k deposition process is the origin for the interface degradation on the conduction band side, while sulfur-vacancy-induced defect-states dominate the interface degradation on the valance band side. The present understanding on the interface properties provides the key to further improving the performance of 2D FETs.