First-Principles Investigation on the Thermoelectric Properties of Layered γ- and γ'-GaSe

Layered compounds have attracted considerable attention owing to their diverse chemical bonding and unique electronic structures. In this study, we give an in-depth study of the thermoelectric properties of γ- and γ'-GaSe by using first-principles calculations combined with Boltzmann transport theory. It is found that both phases are dynamically and thermally stable, as evidenced by their positive phonon frequencies and minimal structural fluctuations at a finite temperature. Interestingly, the valence top of each system is composed of heavy and light bands, which would reduce the significant difference between the in-plane and cross-plane electrical conductivity rooted in many layered systems. Besides, a lower lattice thermal conductivity is observed in γ'-GaSe, which can be attributed to its stronger antibonding states and larger bonding heterogeneity. Combining its favorable electronic transport characteristics, a maximum cross-plane ZT of 2.8 at 600 K can be realized for the p-type γ'-GaSe, revealing its promising potential for thermoelectric conversions.