Fabrication and characteristics of porous germanium films

Porous germanium films with good adhesion to the substrate were produced by annealing GeO 2 ceramic films in H 2 atmosphere. The reduction of GeO 2 started at the top of a film and resulted in a Ge layer with a highly porous surface. TEM and Raman measurements reveal small Ge crystallites at the top layer and a higher degree of crystallinity at the bottom part of the Ge film; visible photoluminescence was detected from the small crystallites. Porous Ge films exhibit high density of holes (10 20 cm −3 ) and a maximum of Hall mobility at ∼225 K. Their p-type conductivity is dominated by the defect scattering mechanism.