Electrochemical Pore Etching in n- and p-Type Ge

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.