Electrochemical pore etching in germanium

Nucleation and growth of electrochemically etched pores in Germanium (Ge) was investigated for n- and p-type Ge single crystals with {1 0 0}, {1 1 0}, and {1 1 1} orientations and doping concentrations of (1014–1018) cm−3. Various types of electrolytes, illumination conditions (front side, back side or none), and pre-treatments for optimizing nucleation were used. Several kinds of macropores could be obtained, mostly for the first time. In particular, pores could be obtained in p-type Ge samples. Pore geometries, morphologies, and growth peculiarities were found to be quite different from other semiconductors. Nucleation is generally difficult, the preferred growth direction is 〈1 0 0〉 or 〈1 1 1〉, stop planes are of {1 1 0} type, and there is always a strong electropolishing component compromising pore geometry and stability. Porous membranes have been produced showing electrocapillarity effects.