Inverse Janus design of two-dimensional Rashba semiconductors

The search for optimal Rashba semiconductors with large Rashba constants, strong electric field responses, and potential thermoelectric properties is pivotal for spin field-effect transistors (SFETs) and Rashba thermoelectric devices. Herein, we employ first-principles calculations to explore the intrinsic Rashba spin splitting in a series of two-dimensional (2D) XYZ(2) (X, Y = Si, Ge, Sn; X not equal Y; Z = P, As, Sb, Bi) monolayers via unnatural inverse Janus structural design. Instead of common Janus-type Rashba systems, the SiSnSb2 and GeSnSb2 monolayers within inverse Janus structures are first predicted as ideal Rashba systems with isolated spin-splitting bands near the Fermi level, and the Rashba constants alpha(R) are calculated as 0.94 and 1.27 eV A, respectively. More importantly, the Rashba effect in such SiSnSb2 and GeSnSb2 monolayers can be more efficiently modulated by the external electric field compared to the biaxial or uniaxial strain, especially with GeSnSb2 monolayer exhibiting a strong electric field response rate of 1.34 e angstrom(2), leading to a short channel length, L = 64 nm. Additionally, owing to the inapplicability of work function and potential energy in assessing built-in electric field (E-in) in inverse Janus SiSnSb2 and GeSnSb2 structures, we further propose an effective method to characterize E-in through a view of fundamental charge transfer to approximately quantize the alpha(R) and its variation under an external electric field. Our work not only proposes the GeSnSb2 monolayer acting as a promising multifunctional material for potential applications in SFETs and Rashba thermoelectric devices but also inspires future research to introduce Rashba spin splitting in 2D materials through inverse Janus design.

Automated summary

In this study, SiSnSb2 and GeSnSb2 monolayers with inverse Janus structures are predicted to have isolated spin-splitting bands near the Fermi level, and the Rashba effect in these monolayers can be more efficiently modulated by the external electric field.