Acoustic phonon limited mobility in two-dimensional semiconductors: Deformation potential and piezoelectric scattering in monolayer MoS2 from first principles (1206.2003v2)

Abstract: We theoretically study the acoustic phonon limited mobility in n-doped two-dimensional MoS2 for temperatures T < 100 K and high carrier densities using the Boltzmann equation and first-principles calculations of the acoustic electron-phonon (el-ph) interaction. In combination with a continuum elastic model, analytic expressions and the coupling strengths for the deformation potential and piezoelectric interactions are established. We furthermore show that the deformation potential interaction has contributions from both normal and umklapp processes and that the latter contribution is only weakly affected by carrier screening. Consequently, the calculated mobilities show a transition from a high-temperature \mu T^{-1} behavior to a stronger \mu T^{-4} behavior in the low-temperature Bloch-Gruneisen regime characteristic of unscreened deformation potential scattering. Intrinsic mobilities in excess of 10^5 cm^2 V^{-1} s^{-1} are predicted at T < 10 K and high carrier densities (n > 10^{11} cm^{-2}). At 100 K, the mobility does not exceed ~7 x 10^3 cm2 V^{-1} s^{-1}. Our findings provide new and important understanding of the acoustic el-ph interaction and its screening by free carriers, and is of high relevance for the understanding of acoustic phonon limited mobilities in general.

• The paper employs first-principles calculations with Boltzmann transport theory to quantify the effects of deformation potential and piezoelectric scattering on electron mobility.
• It distinguishes between normal and umklapp scattering processes, showing distinct temperature dependencies (from T⁻¹ to T⁻⁴) in mobility behavior.
• The study highlights that optimizing scattering mechanisms can enable near-intrinsic mobility, guiding material design for improved 2D semiconductor devices.

Acoustic Phonon Limited Mobility in 2D Semiconductors: Insights from First-Principles Calculations on Monolayer MoS$_2$

This paper offers a comprehensive analysis of acoustic phonon limited mobility in two-dimensional (2D) semiconductors, focusing on monolayer MoS$_2$. The researchers employed first-principles calculations complemented by Boltzmann transport theory to discern how acoustic phonon interactions constrain electron mobility in $n$-doped MoS$_2$, especially at low temperatures and high carrier densities.

Key Findings and Methodology

The paper meticulously calculates the deformation potential (DP) and piezoelectric (PE) scattering mechanisms. These calculations are critical as they influence the electron-phonon (el-ph) interactions pivotal to determining the mobility limits in semiconductors. By incorporating a continuum elastic model with first-principles computations, the authors provide analytic formulations of these mechanisms, elucidating their contributions to overall mobility.

A notable result is the identification of normal and umklapp processes within deformation potential scattering, each contributing differently to mobility. The authors demonstrate that umklapp processes, less affected by carrier screening, significantly influence low-temperature mobility, transitioning from a $\mu \sim T^{-1}$ behavior at higher temperatures to $\mu \sim T^{-4}$ in the Bloch-Grüneisen regime.

Intrinsic mobility calculations predict values exceeding $10^5$ cm$^2$ V$^{-1}$ s$^{-1}$ at temperatures below 10 K for carrier densities $n \gtrsim 10^{11}$ cm$^{-2}$. However, at 100 K, mobility declines to about 7,000 cm$^2$ V$^{-1}$ s$^{-1}$—a reflection of the enhanced scattering effects at elevated temperatures.

Theoretical and Practical Implications

The distinctions made between screened and unscreened scattering offer crucial insights into the intrinsic properties of 2D semiconductors. The differential screening effect, particularly the robustness of umklapp processes against screening, suggests new avenues for engineering higher mobility materials by tuning lattice properties to suppress normal process scattering.

From an applied perspective, achieving near-intrinsic mobilities in technological applications relies on mitigating extrinsic scattering elements, such as impurities and substrate interactions—factors this paper highlights as potentially suppressible through advanced material processing techniques.

Future Directions

This research opens paths for further exploration into transition metal dichalcogenides (TMDs) and similar 2D materials. Given the analogous atomic and electronic structures, findings on MoS$_2$ could be extrapolated to other TMDs, expanding the scope of phonon interaction studies. Moreover, integrating these insights with advancements in materials engineering—such as electrolytic gating to achieve high carrier densities—could enhance the design principles for future 2D electronic and optoelectronic devices.

In conclusion, this paper has provided a detailed analysis of the factors limiting mobility in monolayer MoS$_2$, offering both fundamental insights and practical guidelines for optimizing 2D semiconductor materials.