Point Defects Limited Carrier Mobility in Janus MoSSe monolayer

TL;DR

This work addresses how point defects limit carrier mobility in Janus MoSSe by combining first-principles electron–defect and electron–phonon scattering within a Boltzmann transport framework. It introduces the saturation defect concentration $C_{ m sat}$ to quantify defect tolerance and reveals a defect hierarchy where chalcogen vacancies, especially $V_{ m Se}$, severely degrade mobility, while isovalent substitutions are comparatively benign; oxygen substitutions are particularly detrimental. The methodology, using the PERTURBO framework with explicit e–d matrix elements, yields defect- and temperature-dependent mobilities, offering concrete synthesis targets to maximize mobility and suggesting high sensitivity to trace oxygen could enable chemical sensing. These insights provide materials-specific design rules for MoSSe-based transistors, sensors, and energy devices.

Abstract

Point defects, often formed during the growth of Janus MoSSe, act as built-in scatterers and affect carrier transport in electronic devices based on Janus MoSSe. In this study, we employ first-principles calculations to investigate the impact of common defects, such as sulfur vacancies, selenium vacancies, and chalcogen substitutions, on electron transport, and compare their influence with that of mobility limited by phonons. Here, we define the saturation defect concentration ($C_{\mathrm{sat}}$) as the highest defect density that still allows the total mobility to remain within 90\% of the phonon-limited value, providing a direct measure of how many defects a device can tolerate. Based on $C_{\mathrm{sat}}$, we find a clear ranking of defect impact: selenium substituting for sulfur is relatively tolerant, with $C_{\mathrm{sat}}\approx2.07\times10^{-4}$, while selenium vacancies are the most sensitive, with $C_{\mathrm{sat}}\approx3.65\times10^{-5}$. Our $C_{\mathrm{sat}}$ benchmarks and defect hierarchy provide quantitative, materials-specific design rules that can guide the fabrication of high-mobility field-effect transistors, electronic devices, and sensors based on Janus MoSSe.

Figures (6)

• Figure 1: Atomic structures of defect configurations in a Janus MoSSe monolayer. (a) Top view of the pristine $4 \times 4\times 1$ structure, with a representative defect position highlighted by a red sphere and dashed circle, (b) Se vacancy, (c) S vacancy, (d) S/O/Te atom substituting at the Se vacancy site, and (e) Se/O/Te atom substituting at the S vacancy site.
• Figure 2: Orbital‐projected band structure of the MoSSe monolayer along the high‐symmetry path. Circle areas scale with the projection weight onto Mo (blue), Se (red), and S (yellow) orbitals.
• Figure 3: Electron mobilities in defected MoSSe as functions of carrier concentration at 300 K. Calculations include phonon‐limited mobility (solid line) and combined defect‐ and phonon‐limited mobility (dashed line).
• Figure 4: Combined defect and phonon-limited electron mobility in defected MoSSe as a function of defect concentration $C_d$. The phonon-limited mobility is $\mu_{\text{e-ph}} = 59.34$ cm$^{2}$V$^{-1}$s$^{-1}$ at a carrier concentration of $1.2 \times 10^{13}$ cm$^{-2}$.
• Figure 5: (a)-(b) Electron mobility in defected MoSSe as a function of temperature at a carrier concentration of $1.0 \times 10^{13}$ cm$^{-2}$, including the phonon-limited mobility (solid line) and the combined defect- and phonon-limited mobility (dashed line).