Ultraviolet-ozone treatment: an effective method for fine-tuning optical and electrical properties of suspended and substrate-supported MoS2

TL;DR

UV-O3 treatment effectively tunes the optical and electrical properties of MoS2, with substrate presence influencing the extent of property modifications, enabling controlled doping and property optimization for device applications.

Contribution

This study provides detailed insights into how UV-O3 treatment affects MoS2's properties, highlighting the substrate's role and identifying optimal treatment conditions for desired electronic and optical characteristics.

Findings

UV-O3 treatment quenches PL in substrate-supported MoS2 more than in suspended flakes.

4 minutes of UV-O3 optimally induces p-type doping while preserving PL.

Extended UV-O3 exposure (>6 min) reduces electron density and harms hole transport.

Abstract

Ultraviolet-ozone (UV-O3) treatment is a simple but effective technique for surface cleaning, surface sterilization, doping and oxidation, and is applicable to a wide range of materials. In this study, we investigated how UV-O3 treatment affects the optical and electrical properties of molybdenum disulfide (MoS2), with and without the presence of a dielectric substrate. We performed detailed photoluminescence (PL) measurements on 1-7 layers of MoS2 with up to 8 minutes of UV-O3 exposure. Density functional theory (DFT) calculations were carried out to provide insight into oxygen-MoS2 interaction mechanisms. Our results showed that the influence of UV-O3 treatment on PL depends on whether the substrate is present, as well as the number of layers. The PL intensity of the substrate-supported MoS2 decreased dramatically with the increase of UV-O3 treatment time and was fully quenched after 8 mins. However, the PL intensity of the suspended flakes was less affected. 4 minutes of UV-O3 exposure was found to be optimal to produce p-type MoS2, while maintaining above 80% of the PL intensity and the emission wavelength, compared to pristine flakes (intrinsically n-type). Our electrical measurements showed that UV-O3 treatment for more than 6 minutes not only caused a reduction in the electron density but also deteriorated the hole-dominated transport. It is revealed that the substrate plays a critical role in the manipulation of the electrical and optical properties of MoS2, which should be considered in future device fabrication and applications.