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 por e dimensions and the structure of the porous layer depend on the dopin g density and the crystallographic orientation of the surface. The por e morphology of porous GaAs is essentially independent of the applied current. The pore front velocity is linearly proportional to the curre nt and the porous layer can be grown to any thickness. The primary por es in GaAs grow in the [111] a direction which is in contrast with sil icon where the pores grow in the [100] direction. The pore diameters i ncrease from 80 nm for highly doped GaAs to 400 nm for undoped GaAs. T he combination of electrochemical methods and structural analysis tech niques, including transmission electron microscopy and small angle neu tron scattering, leads to a better understanding of anisotropic etchin g of semiconductors. (C) 1997 Elsevier Science B.V.