UNCONVENTIONAL STRUCTURED SEMICONDUCTORS AND THEIR APPLICATIONS IN OPTOELECTRONICS AND PHOTOVOLTAICS BY

ii “Unconventional structured semiconductors ” have novel structures that provide improved optical and electrical properties compared with the conventional crystalline semiconductors. Two kinds of semiconductors are discussed within this thesis: gallium nitride (GaN) and silicon (Si). A novel Pt-assisted electroless etching technique is used to produce porous GaN (PGaN), which is of particular interest for optoelectronics due to its large direct bandgap (3.4 eV). PGaN is also promising for use as a substrate for epitaxial growth and for chemical and biosensing. Several possible applications for PGaN have been explored. PGaN is able to be functionalized for use as a surface enhanced Raman spectroscopy (SERS) substrate by solution-based electroless deposition and vacuum evaporation of Au and Ag. SERS enhancement factors of up to 108 have been observed for Ag-coated porous GaN. Other efforts are focused on using the porous film as conductivity sensors. The improved optical properties observed in porous Ga