Enhancement of the thermoelectric power factor of MnSi1.7 film by modulation doping of Al and Cu

It is well known that aluminum (Al) and copper (Cu) are acceptor impurities with shallow- and deep-energy levels in silicon (Si), respectively. The thermoelectric power factor of Al and Cu codoped Si film is larger than that of only Al-doped Si film. In this report, the Al and Cu codoped Si layer, Si: (Al + Cu), is used as a barrier layer, while a higher manganese silicide (HMS, MnSi1.7) layer is used as a well layer to enhance the power factor of MnSi1.7 film. It is found that the Al and Cu modulation doped MnSi1.7 film, Si: (Al + Cu)/MnSi1.7, has a power factor almost two times larger than that of only Al modulation doped MnSi1.7 film, Si: Al/MnSi1.7. It is also found that an undoped Si spacer layer between the Si: (Al + Cu) barrier layer and the MnSi1.7 well layer can enhance the power factor further. Finally, it is demonstrated that the MnSi1.7 film with double Si barrier layers, Si: (Al + Cu)/MnSi1.7/Si: (Al + Cu), has the highest power factor, 1423×10−6 W/m K2 at 783 K, which is very close to that of MnSi1.7 bulk material.