F. Möller

Bio: F. Möller is an academic researcher from Technische Universität München. The author has contributed to research in topics: Porous silicon & Etching (microfabrication). The author has an hindex of 3, co-authored 3 publications receiving 432 citations.

Hopping transport on a fractal: ac conductivity of porous silicon.

Abstract: We have measured the frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz-100 kHz at different temperatures. The conductivity data exhibit a strong frequency dependence. When normalized to the dc conductivity, our data obey a universal scaling law, with a well-defined crossover, in which the real part of the conductivity sigma' changes from an sqrt(omega) dependence to being proportional to omega. We explain this in terms of activated hopping in a fractal network. The low-frequency regime is governed by the fractal properties of porous Si, whereas the high-frequency dispersion comes from a broad distribution of activation energies. Calculations using the effective-medium approximation for activated hopping on a percolating lattice give fair agreement with the data.

Nonlinear electrical transport in porous silicon.

Abstract: We present a study of the electrical transport in porous Si layers prepared by anodic etching of two different kinds of (100) p-type Si substrates. It is shown that by choosing a sufficiently thick layer, the problem of injection from the contacts can be eliminated. In this way we measure the intrinsic transport properties. The results suggest that a Poole-Frenkel type of mechanism accounts for the observed electric-field-enhanced conduction.

Band alignment and carrier injection at the porous‐silicon–crystalline‐silicon interface

Abstract: The current‐voltage characteristics and the photoresponse of metal‐porous Si–p‐type Si heterostructures have been studied. It is shown that the common interpretation of the current‐voltage characteristics, which assumes that the current is limited by the Schottky barrier at the metal‐porous Si interface, is wrong. An alternative explanation based on the electric‐field dependence of the porous Si conductivity is suggested. It is shown that the rectifying behavior originates from a depletion inside the c‐Si substrate at its interface to the porous Si.

Synergism in binary nanocrystal superlattices leads to enhanced p-type conductivity in self-assembled PbTe/Ag2Te thin films

Abstract: The ordered cocrystallization of nanoparticles into binary superlattices enables close contact of nanocrystals with distinct physical properties, providing a route to 'metamaterials' design. Here we present the first electronic measurements of multicomponent nanocrystal solids composed of PbTe and Ag(2)Te, demonstrating synergistic effects leading to enhanced p-type conductivity. First, syntheses of size-tuneable PbTe and Ag(2)Te nanocrystals are presented, along with deposition as thin-film nanocrystal solids, whose electronic transport properties are characterized. Next, assembly of PbTe and Ag(2)Te nanocrystals into AB binary nanocrystal superlattices is demonstrated. Furthermore, binary composites of varying PbTe-Ag(2)Te stoichiometry (1:1 and 5:1) are prepared and electronically characterized. These composites show strongly enhanced (conductance approximately 100-fold increased in 1:1 composites over the sum of individual conductances of single-component PbTe and Ag(2)Te films) p-type electronic conductivity. This observation, consistent with the role of Ag(2)Te as a p-type dopant in bulk PbTe, demonstrates that nanocrystals can behave as dopants in nanostructured assemblies.

Doubling Exponent Models for the Analysis of Porous Film Electrodes by Impedance. Relaxation of TiO2 Nanoporous in Aqueous Solution

Abstract: The paper is concerned with the small signal ac impedance of porous film electrodes in contact with solution. An overview is presented of the standard transmission line model with two transport channels and a crosswise element. The simplest configurations are discussed: a single resistance in one of the channels, and either an interfacial capacitor or a RC transfer circuit at the pore's wall. The resulting relaxation functions are classified in terms of two characteristic frequencies: one for coupled transport and interfacial polarization and another one for the interfacial reaction. Subsequently, these models are extended in order to describe porous electrodes where the interfacial polarization displays complex properties, i.e., frequency dispersion. The capacitive element is described by a constant-phase element (CPE), and it is shown that the fractionary exponent provides an additional and measurable degree of freedom in the parameter space of the relaxation function, whose determination can be explo...