Electroless deposition of gold and platinum for metallization of the intrapore space in porous gallium nitride

The metallization of porous gallium nitride (PGaN) via electroless deposition of Au and Pt is presented. PGaN is generated via the Pt-assisted electroless etching of hydride vapor phase epitaxy GaN. Ultrathin Pt films are sputtered onto the GaN surface, and etching is carried out in a 1:2:2 solution of CH3OH:HF:H2O2. In the case of electrodeposition of Au, the reduction of a Au plating solution by formaldehyde results in the deposition of Au particles which tend to cluster and fill the nanopores. The high surface activity of Au towards PGaN biases Au deposition on PGaN toward cluster formation. For Pt, either Pt clusters or thin film coatings can be obtained by the careful selection of the deposition bath conditions. More importantly, in all cases the electroless deposition of metals on PGaN is extremely sensitive to the conditions of the surface and the plating bath. In particular there is a fine line between conditions which produce smooth coatings and those resulting in clustering. Moreover, the narrow size of the pores, on the order of 80 nm, raises issues of mass transport of the metal plating solution inside the pores, contributing to the production of clustered deposits. Overall the electroless deposition process is more controllable for the deposition of Pt than of Au.