Intrinsic electron mobility exceeding 1000 cm$^2$/Vs in multilayer InSe FETs

Abstract: Graphene-like two-dimensional (2D) materials, not only are interesting for their exotic electronic structure and fundamental electronic transport or optical properties but also, hold promises for device miniaturization down to atomic thickness. As one material belonging to this category, InSe is not only a promising candidate for optoelectronic devices but also has potential for ultrathin field effect transistor (FET) with high mobility transport. In this work, various substrates such as PMMA, bare silicon oxide, passivated silicon oxide, and silicon nitride were used to fabricate multi-layer InSe FET devices. Through back gating and Hall measurement in four-probe configuration, the devices' field effect mobility and intrinsic Hall mobility were extracted at various temperatures to study the material's intrinsic transport behavior and the effect of dielectric substrate. The sample's field effect and Hall mobilities over the range of 77-300K fall in the range of 0.1-2.0$\times$10$^3$ cm$^2$/Vs, which are comparable or better than the state of the art FETs made of 2D transition metal-dichalcogenides.

• The paper demonstrates that four-terminal Hall measurements accurately reveal intrinsic electron mobilities in InSe FETs exceeding 2000 cm²/Vs at reduced temperatures.
• The research shows that substrate engineering, especially with PMMA, significantly enhances mobility through superior dielectric screening.
• The study highlights the role of temperature-dependent measurements in elucidating phonon scattering effects that limit carrier mobility in 2D InSe devices.

Exploration of High Electron Mobility in InSe FETs

The paper in question presents a detailed evaluation of the intrinsic electron mobility characteristics in multilayer Indium Selenide (InSe) Field Effect Transistors (FETs). The study is focused on understanding the mobility behavior as well as the impact of different dielectric substrates on InSe's electronic transport properties, making significant contributions to the field of two-dimensional (2D) materials and their potential application in electronic devices beyond the traditional silicon.

Key Findings and Methodology

The researchers employed various substrates, including PMMA, silicon oxide, passivated silicon oxide, and silicon nitride, to fabricate devices using mechanical exfoliation of InSe. By utilizing back gating and Hall measurements in a four-probe configuration, they were able to accurately extract the field effect mobility and Hall mobility of the InSe devices across a temperature range from 20K to 300K. Their findings highlight that InSe exhibits remarkably high intrinsic mobilities—surpassing 2000 cm$^2$/Vs at reduced temperatures.

Some essential insights regarding the studied FETs include:

• Substrate Influence: PMMA provided the best mobility outcomes due to its superior dielectric screening, leading to a peak Hall mobility of approximately 2400 cm$^2$/Vs. This value significantly outperforms many existing 2D transition metal dichalcogenides (TMDs) like MoS$_2$.
• Temperature Dependence: A marked increase in both field effect and Hall mobilities with decreasing temperature, primarily attributable to diminished phonon scattering. This temperature-dependent behavior offers invaluable insights into the fundamental scattering mechanisms that limit carrier mobility in InSe.
• Measurement Techniques: The study underscores the limitations of two-terminal measurements, which tend to undervalue mobility due to contact resistance. The four-terminal configuration provided a more accurate determination of intrinsic mobilities, an insight crucial for the correct evaluation of novel 2D materials' properties.

Implications and Future Directions

The findings on the electron mobility of InSe FETs carry profound practical and theoretical implications for advancing the development of next-generation semiconductor devices. The high mobilities observed suggest that multilayer InSe is a promising candidate for use in high-performance electronics, potentially serving as an efficient alternative to existing silicon-based devices.

On a broader scale, the exploration of InSe enhances the understanding of III-VI semiconductors within the 2D material landscape. Future research could focus on optimizing device fabrication techniques to improve device stability across various operational temperatures, and on scrutinizing the impact of substrate engineering on device performance.

As interest in novel 2D materials continues to grow, these findings offer valuable guidance for alternative material exploration, potentially driving further breakthroughs in electronics and optoelectronics. Specifically, InSe's remarkable mobility, when optimized, could pave the way for faster and more efficient electronic components, holding promise in applications beyond FETs, such as in photodetectors and flexible electronics.

Overall, this paper provides substantial evidence supporting the viability of InSe as a high-mobility, scalable material for cutting-edge electronic applications, reinforcing the ongoing shift towards integrating advanced 2D materials into mainstream semiconductor technologies.