Conductive Network-Mediated Charge Transport and Phonon Dynamics in MSe/MTe (M = Ga, In) Superlattices for Enhanced Thermoelectric Performance

Superlattice (SL) engineering offers a rational pathway to high-performance thermoelectrics by integrating electronic structure tuning with phonon transport suppression. In this context, we explore the MSe/MTe (M = Ga, In) SL using first-principles calculations combined with the Boltzmann transport theory. The introduction of an MTe-based sublayer upon an MSe sublayer generates a conductive network that enhances carrier mobility and electrical conductivity, while simultaneously reshaping lattice dynamics. In GaSe/GaTe, phonon softening reduces acoustic group velocities, whereas InSe/InTe exhibits pronounced flat phonon branches and avoided crossings that open additional scattering channels. Moreover, the splitting and localization of mid-frequency optical modes within specific sublayers further disrupt phonon propagation and strengthen anharmonic interactions. These mechanisms collectively suppress lattice thermal conductivity to 1.6 W/mK for GaSe/GaTe and 1.0 W/mK for InSe/InTe at 300 K, which is almost half that of their bulk counterparts. On the electronic side, GaSe/GaTe benefits from band convergence that enhances the Seebeck coefficient, while InSe/InTe achieves superior conductivity and a maximum power factor of 1.94 × 10–3 W/mK2 at 700 K. The cooperative optimization of electronic and phonon transport yields outstanding thermoelectric performance with a figure of merit reaching ∼3.1 (p-type) and ∼2.7 (n-type) for InSe/InTe at 700 K, surpassing the Ga-based SL. These results establish SL engineering as a strategic pathway for achieving next-generation, high-efficiency, and environmentally benign thermoelectric materials.