Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California 92093, United States.
Nano Lett. 2013 Mar 13;13(3):1196-202. doi: 10.1021/nl304619u. Epub 2013 Feb 12.
We experimentally studied the thermoelectric power factor of hole gas in individual Ge-Si core-shell nanowires with Ge core diameters ranging from 11 to 25 nm. The Ge cores are dopant-free, but the Fermi level in the cores is pinned by surface and defect states in the epitaxial Si shell thereby doping the cores into the degenerate regime. This doping mechanism avoids the high concentration of dopants usually encountered in bulk thermoelectric materials and provides a unique opportunity to enhance the carrier mobility with suppressed ionized impurity scattering. Moreover, the carrier concentration in small diameter nanowires has also been effectively modulated by field effect, allowing one to probe the electrical conductivity and thermopower within a wide range of carrier concentrations, which is crucial to understand the thermoelectric transport behavior. We found that the thermopower of nanowires with Ge core diameters down to 11 nm still follows the behavior of bulk Ge. As a result, the power factor is found to be closely correlated with the carrier mobility, which is higher than that of bulk Ge in one of the core-shell nanowires studied here.
我们通过实验研究了直径为 11 至 25nm 的 Ge-Si 核壳纳米线中孔气的热电功率因子。这些 Ge 核是无掺杂的，但费米能级被外延 Si 壳中的表面和缺陷态钉扎，从而将核掺杂到简并区。这种掺杂机制避免了在体热电材料中通常遇到的高浓度掺杂剂，并提供了一个独特的机会，通过抑制离子杂质散射来提高载流子迁移率。此外，小直径纳米线中的载流子浓度也通过场效应得到了有效调节，从而可以在很宽的载流子浓度范围内探测电导率和热电势，这对于理解热电输运行为至关重要。我们发现，直径降至 11nm 的 Ge 核纳米线的热电势仍遵循体 Ge 的行为。因此，功率因子与载流子迁移率密切相关，在我们研究的核壳纳米线之一中，其迁移率高于体 Ge。
