INITIATION AND FORMATION OF POROUS GAAS

The present work deals which localized dissolution processes (pit and port initiation and growth) of p- and n-type (100) GaAs. Pit and pore growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-hype ma terial, localized dissolution is only observed if a passivating film i s present on the surface, otherwise, e.g., in acidic solutions, the ma terial suffers from a uniform attack (electropolishing) which is indep endent of the anion present. In contrast, localized dissolution (pitti ng corrosion) and pore formation on n-type material can be triggered i ndependent of the presence of an oxide film. This is explained in term s of the different current limiting factor for the differently doped m aterials (oxide film in the ease of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by sc anning electron microscopy, energy dispersive x-ray analysis, and Auge r electron spectroscopy, and consists mainly of GaAs. From scratch exp eriments it is clear that the pit initiation process is strongly influ enced by surface defects. For n-type material, atomic force microscopy investigations show that light induced roughening of the order of sev eral hundred nanometers occurs under nonpassivating conditions. This n anometer-scale roughening however does not affect the pitting process.