
To illustrate how the different scattering mechanisms affect , in Fig. 6.2 we show when only electronphonon scattering is considered for the electronic system and only phononphonon scattering is considered for the phononic system. Results for type nanowires are shown in Fig. 6.2a, and results for type nanowires in Fig.6.2b. Further below, in Fig.6.3, we include the effect of boundary scattering for both systems. We consider nanowires of diameters from to in three different orientations, (blue lines), (red lines), and (green lines). We assume a carrier concentration of , which is close to the concentration where the maximum of the power factor is observed. in Fig. 6.2 shows a considerable orientation and diameter dependence. For type nanowires, the reaches values of in the best case (for the nanowires and diameters above ). In the worst case, is significantly lower at only , which is achieved for the lowest diameters, as well as for the nanowire in the entire diameter range. for these particular nanowires suffers from their large thermal conductivities as shown in Fig. 6.1 ( higher compared to the other orientations). type nanowires have lower values, below for most cases. A significant increase is observed in the cases of the and nanowires with decreasing diameter, which can be attributed to the improvement of their electrical conductivity [143] since the bandstructures of these nanowires undergo significant modifications with confinements and their hole effective mass is significantly reduced [144]. For both type, and type nanowires, the orientation provides the best performance. The reduction in the thermal conductivity due to phonon confinement, therefore, increases by an order of magnitude compared to the bulk value ( ).