At T = 1000 K and the lowest n = 10 16 cm -3 we studied the S are on the order of -1200 µV K -1 and decrease monotonically with n to around -50 µV K -1 at n = 10 22 cm -3 . On the other hand, the σ are negligible up to n ≈ 10 19 cm -3 and increase sharply at higher carrier concentrations. The increase in the conductivity dominates the PF S 2 σ up to n ∼ 10 21 -5 × 10 22 cm -3 cm -3 , while at larger n the decrease in S becomes dominant, which combine to form a maximum in the PF. We therefore conclude that carrier concentrations above ∼ 10 19 cm -3 are necessary to obtain a reasonable PF, but very high n are detrimental. On the other hand, the κ el increases with σ following the Wiedemann-Franz law: