Screening effect on the phonon drag induced seebeck coefficient in bilayer graphene/quasi-two-dimensional electron gas structures

Abstract

In this work, we investigate the impacts of the temperature-dependent screening effect on the Seebeck coefficient originating from the phonon drag, namely phonon—drag thermopower S g , of a double layer system consisting of bilayer graphene (BLG) separated from a quasi-two-dimensional electron gas (q2DEG) by an air medium (hereafter referred to as BLG-q2DEG). For such a system, we can assume that the two-dimensional (2D) electrons in BLG only interact internally with acoustic phonons. We consider the effects of screening induced by the 2D electrons in q2DEG on the electron–phonon interactions in BLG by comparing with the results obtained when only using the monolayer screening function in BLG. The monolayer screening functions in BLG (q2DEG) do not depend on the distance d between the two layers, and the screening function of the double layer system approaches the respective monolayer screening functions for large d. When taking into account of the screening effect caused by charged carriers in both layers, S g of a BLG-q2DEG decreases compared to the case of only considering the monolayer screening effect, especially in the low-T regime. With different carrier densities in the two layers NsBLG≠NsGaAs, it has shown that S g strongly depends on BLG. Besides, when changing the width L of the q2DEG such as GaAs quantum well, the double layer screening function makes S g increase for small L and negligibly affects S g for large L. On the contrary, the monolayer screening functions make S g decrease for large L. The monolayer screening functions cause S g to increase for NsBLG<NsGaAs.