Effect of screening on seebeck coefficient in bilayer graphene/AlGaAs electron gas

Abstract

The knowledge of Seebeck coefficient is a key factor in optimization of thermoelectric materials and finding right applications for it. A high sensitivity to structural change makes thermopower measurements an excellent technique for the study on the charge transport properties of a given material. The phonon-drag term dominates at low temperature in the Seebeck coefficient. This study examines the temperature-dependent screening effect on the phonon-drag-induced Seebeck coefficient ($S^g$) in a bilayer graphene (BLG)-AlGaAs/quasi-two-dimensional electron gas (q2DEG) system at the temperature below 50 K. The BLG layer interacts with both deformation potential acoustic phonons and stronger piezoelectric field acoustic phonons from AlGaAs/GaAs. We compare the electron–phonon interactions in BLG with and without screening by q2DEG. The screening effect reduces $S^g$, particularly at low temperatures, and shows a strong dependence on the carrier density in the BLG layer. The double-layer screening function increases $S^g$ with layer separation (d), paralleling the monolayer screening at large d. Additionally, varying the GaAs quantum well width reveals that $S^g$ increases with width less than 100 Å under double-layer screening but remains unchanged beyond this threshold, while monolayer screening decreases $S^g$ as the width increases. Both screening functions enhance $S^g$ when the BLG carrier density is lower than that of q2DEG, though the magnitude difference between them is minimal.