The photogalvanic effect in 2D van der Waals heterojunctions M2XT2/SiC via first-principles calculations

Abstract

This first-principles study systematically investigates the structural, electronic, and optoelectronic properties of M₂XT₂/SiC (M = Sc, Y; X = C; T = F, Cl, Br) van der Waals heterojunctions. The four examined systems (Sc₂CBr₂/SiC, Sc₂CCl₂/SiC, SiC/Y₂CF₂, and SiC/Y₂CCl₂) retain their monolayer band characteristics while forming stable heterojunctions with indirect bandgaps. The first three configurations clearly show that the VBM and CBM are confined in SiC and M₂XT₂, respectively, indicating a type-II band alignment. However, for SiC/Y₂CF₂, both the VBM and CBM are confined in Y₂CF₂, indicating a type-I band alignment. Notably, SiC/Y₂CCl₂ demonstrates exceptional electron mobility (6.99 × 10³ cm² V⁻¹ s⁻¹). Charge density difference analysis reveals electron transfer from SiC to MXene layers, facilitated by a built-in electric field that suppresses carrier recombination. All heterojunctions exhibit enhanced light absorption and reduced bandgaps compared to SiC, with SiC/Y₂CF₂ showing an optimal photoresponse at 3.2 eV photon energy and the highest extinction ratio. These findings highlight the potential of MXene/SiC heterojunctions for tailored optoelectronic applications.