Papers by Author: Helmut Föll

Abstract: In this work we present a theoretical model that explains the current and voltage oscillations at the Si electrode in HF media. A simulation computer program based on this model is implemented and results are shown. Oscillations of the current and (for the first time) the voltage obtained numerically fit perfectly with experiments. The model allows to obtain more information about the system in the form of maps (accompanied by histograms) of e.g.: oxide thickness distribution, SiO2/HF and Si/SiO2 interfaces morphology, or local voltage losses. Other characteristics of the oxide like capacitance or roughness can also be obtained.

Abstract: Little was known about porous Ge until recently; here some substantial progress in producing porous Ge will be reported, mostly for the first time. i) n-type Ge in aqueous solution: Pore geometries, morphologies and growth peculiarities were found to be quite different from other semiconductors, such as Si and III-V. Nucleation is generally difficult, the preferred growth direction is <100> (and <111>), major stop planes are of the {110} type, but others are also found. In addition, there is always a strong electropolishing component compromising pore geometry and stability. ii) n- and p-type Ge in organic solution: In DMSO solution, the growth direction is <111>, and the stopping planes are still mainly {110}; somewhat unexpected, because this has never been observed in Si, and because no pores have been found in other p-type semiconductors so far, with the exception of Si. Nucleation seems to be difficult too, and new domain-forming phenomena are observed. Smooth or rough pore walls can be obtained, dependent on the experimental conditions.