The introduction of an un-doped silicon layer (spacer) enhances significantly the thermoelectric power factor in modulation-doped Si(Al)-MnSi 1.7 -Si(Al) sandwich structure. This un-doped silicon layer is inserted between the MnSi 1.7 (HMS) and Al-doped silicon layers. With a proper spacer thickness, the electrical resistivity decreases sharply and is weakly dependent on temperature from 300 K to 683 K. As a result, the thermoelectric power factor can reach 0.973 × 10 −3 W/m-K 2 at 683 K, which is about ten times larger than that of an ordinary MnSi 1.7 film without modulation doping.
We have explored the ion-modulated electronic transport properties of mixed ionic-electronic conductor (MIEC) composite nanostructures made of superionic conductor RbAg4I5 films and carbon nanotube (CNT) bundle spiderwebs. Our experimental and theoretical studies indicate that the formation of ion-electron bound states (IEBSs) leads to strong ion-electron interference effect and interesting electronic transport of CNT, such as nonlinear current-voltage (I–V) characteristics and novel temperature dependence of the current. With increasing temperature, the hybrid nanostructures show rich phases with different dependence of current on temperature, which is related to the structural phase transition of RbAg4I5 and the transition of dissociation of IEBSs. The ion-modulation of the electric conductivity in such MIEC composite nanostructures with great tunability has been used to design new ionic-electronic composite nano-devices with function like field effect transistor.
Phonon-drag effect usually occurs in single crystals at very low temperatures (10–200 K). Strong phonon-drag effect is observed in ultra-thin β- FeSi 2 films at around room temperature. The Seebeck coefficient of a 23 nm-thick β- FeSi 2 film can reach -1.375 mV/K at 343 K. However, the thermoelectric power factor of the film is still small, only 0.42×10-3 W/m-K2, due to its large electrical resistivity. When a 27 nm-thick MnSi 1.7 film with low electrical resistivity is grown on it, the thermoelectric power factor of the MnSi 1.7 film can reach 1.5×10-3 W/m-K2 at around room temperature. This value is larger than that of bulk MnSi 1.7 material in the same temperature range.
The influence of an AlO x oxide or Si interlayer on the thermoelectric power factor of the higher manganese silicide (HMS, MnSi y, y = 1.73–1.75) film deposited on quartz substrate is investigated. The HMS film and the interlayer are prepared on quartz substrate by magnetron sputtering of MnSi 2, Al , Si and Si : B (1 at.% B content) targets. It is found that the metallic phase MnSi is present in the semiconducting HMS film without an interlayer, resulting in a lower Seebeck coefficient, 0.160 mV/K, but not a lower electrical resistivity, 0.021 Ω ⋅cm at 683 K. The thermoelectric power factor is only 122 × 10-6 W/mK2 at 683 K. On the other hand, the metallic phase MnSi disappears and the Seebeck coefficient restores to its high value after using the AlO x oxide or Si interlayer. Besides, the electrical resistivity decreases by using the AlO x oxide or Si : B interlayer. The HMS film with an Si : B interlayer has the highest Seebeck coefficient, 0.247 mV/K, and the lowest electrical resistivity, 0.011 Ω ⋅cm, at 683 K. Thus, the thermoelectric power factor is enhanced and can reach 555 × 10-6 W/mK2 at 683 K.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.