ENHANCEMENT OF THERMOELECTRIC POWER FACTOR BY A SILICON SPACER IN MODULATION-DOPED Si-HMS-Si

Abstract

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.

Enhancement of thermoelectric power factor of MnSi1.7 films by Si addition and modulation doping

“…The size of the glass substrate was 25 × 25 × 1 mm 3 . The film thickness was monitored in situ by a quartz oscillator and measured by a cross‐sectional image of scanning electron microscope 24. All the films were deposited on glass substrates at 753 K, and then thermally annealed at 823 K for 40 min in high vacuum.…”

“…But the film thickness was reduced to 16 nm, and an Al‐doped polycrystalline silicon layer was grown on the MnSi 1.7 layer to realize the modulation doping, as shown in Fig. 1(b) 24. The number after the capital letters A and B represents the sputtering power of Si target.…”

“…Sample BL was made with similar parameters as those of the barrier layers of samples B0 and B40. Sample WL is a pure MnSi 1.7 film with a thickness of 16 nm 24. Of course, aluminum in the silicon layer can diffuse into the MnSi 1.7 layer, as evidenced by the Auger electron spectroscopy 24.…”

“…Sample WL is a pure MnSi 1.7 film with a thickness of 16 nm 24. Of course, aluminum in the silicon layer can diffuse into the MnSi 1.7 layer, as evidenced by the Auger electron spectroscopy 24. Since aluminum dissolves in silicon and MnSi 1.7 to very low extent, most of them must be located in the grain boundaries of the films 27, 28.…”

“…Thus a spatial separation of carriers from their parent impurities in the barrier layer is achieved, the carrier mobility is increased, and the electrical resistivity is reduced. Indeed, enhancement of power factor has been reported in quantum‐well structures 22–24, even in bulk nano‐composites 25, by using the concept of modulation doping.…”