title: High Seebeck Coefficient of Porous Silicon: Study of the Porosity Dependence.
abstract: In-plane Seebeck coefficient of porous Si free-standing membranes of different porosities was accurately measured at room temperature. Quasi-steady-state differential Seebeck coefficient method was used for the measurements. A detailed description of our home-built setup is presented. The Seebeck coefficient was proved to increase with increasing porosity up to a maximum of ~1 mV/K for the ~50 % porosity membrane, which is more than a threefold increase compared to the starting highly doped bulk c-Si substrate. By further increasing porosity and after a maximum is reached, the Seebeck coefficient sharply decreases and stabilizes at ~600 μV/K. The possible mechanisms that determine this behaviour are discussed, supported by structural characterization and photoluminescence measurements. The decrease in nanostructure size and increase in carrier depletion with increasing porosity, together with the complex structure and morphology of porous Si, are at the origin of complex energy filtering and phonon drag effects. All the above contribute to the observed anomalous behaviour of thermopower as a function of porosity and will be discussed.
authors.affiliation: Institute of Nanoscience and Nanotechnology (INN), NCSR Demokritos, Terma Patriarchou Grigoriou and Neapoleos, Athens, 153 10, Greece.
authors.forename: Katerina
authors.initials: K
authors.lastname: Valalaki
authors.affiliation: IMEP-LAHC, Grenoble Institute of Technology - Minatec, Parvis Louis Neel 3, Grenoble, 38016, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Benech
authors.affiliation: Institute of Nanoscience and Nanotechnology (INN), NCSR Demokritos, Terma Patriarchou Grigoriou and Neapoleos, Athens, 153 10, Greece. a.nassiopoulou@inn.demokritos.gr.
authors.forename: Androula
authors.initials: A
authors.lastname: Galiouna Nassiopoulou
keywords: Low-dimensional semiconductors; Porous Si; Seebeck coefficient; Thermoelectrics