Thermoelectric Properties of a Semiconductor Quantum Dot Chain Connected to Metallic Electrodes

The thermoelectric properties of a semiconduct quantum dot chain (SQDC) connected to metallic electrodes are theoretically investigated in the Coulomb blockade regime. An extended Hubbard model is employed to simulate the SQDC system consisted of {\color{blue}N=2,3,4, and 5} quantum dots (QDs). The charge and heat currents are calculated in the framework of Keldysh Green's function technique. We obtained a closed-form Landauer expression for the transmission coefficient of the SQDC system with arbitrary number of QDs by using the method beyond mean-field theory. The electrical conductance ($G_e$), Seebeck coefficient (S), thermal conductance, and figure of merit (ZT) are numerically calculated and analyzed in the linear response regime. When thermal conductance is dominated by phonon carriers, the optimization of ZT is determined by the power factor ($pF=S^2G_e$). We find that the optimization of ZT value favors the following conditions:(1) QDs with low energy level fluctuations, (2) QD energy levels lie above the Fermi level of electrodes, (3) $Γ< t_c \ll U_0$, where $t_c$, $U_0$, and $Γ$ are electron interdot hopping strength, on-site electron Coulomb interaction, and tunneling rate, respectively, and (4) $Γ_L=Γ_R$ with $Γ_L+Γ_R$ kept constant, where $Γ_L (Γ_R)$ is the left (right) tunneling rate. It is predicted that high ZT values can be achieved by tailoring above conditions.

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