The formation of porous GaAs in HF solutions

The electrochemical etching of n-type GaAs in HF solutions in the dark results in the formation of a porous layer. The pore density, the pore dimensions and the structure of the porous layer depend on the doping density and the crystallographic orientation of the surface. The pore morphology of porous GaAs is essentially independent of the applied current. The pore front velocity is linearly proportional to the current and the porous layer can be grown to any thickness. The primary pores in GaAs grow in the [111] a direction which is in contrast with silicon where the pores grow in the [100] direction. The pore diameters increase from 80 nm for highly doped GaAs to 400 nm for undoped GaAs. The combination of electrochemical methods and structural analysis techniques, including transmission electron microscopy and small angle neutron scattering, leads to a better understanding of anisotropic etching of semiconductors. (C) 1997 Elsevier Science B.V.