Abstract
Porous GaAs can be formed electrochemically (in a suitable electrolyte) by polarizing the material anodically to a critical potential value - the pore formation potential (PFP). Propagation of pores can be achieved on p-and n-type substrates of different orientations {(100) and (110)} and in different electrolytes (HCl, HF, and HBr). The threshold potential for pore formation (PFP) strongly depends on substrate doping, but only weakly depends on the type and concentration of the halogen anion present in the solution and the orientation of the material. For n-type samples (in the dark) the PFP can partially be explained by a breakdown of the Schottky barrier at the corresponding electrochemical potential. However, chemical factors in the breakdown process have to be considered, as well. The morphology of the resulting structure is greatly influenced by the type of anions and the substrate orientation. In HCl, a wide size distribution of porosity including very fine porosity is obtained, whereas in HBr and I-IF a coarser feature size is obtained. For all electrolytes, the attack occurred preferentially at randomly distributed locations. The most uniform attack was obtained In HCl solution. The morphology of the porous structure is consistent with an exposure of {111} crystallographic planes, which have a lower kinetic reactivity than other crystal planes.