| The major work concentrates on the details of the physical aspects of electrochemical etching of 4H and 6H silicon carbide. The investigation of porous morphologies in n-type as well as in p-type crystals is conducted as a function of etching parameters. The photoassisted electrochemical etching of highly doped n-type 4H SiC under low voltage and/or low current conditions is analyzed in detail. The etching of four major crystallographic planes of hexagonal SiC is discussed: the Si-face or (0001), the C-face or (0001¯), the P-face or (11¯00), and the A-face or (12¯10). The resultant triangular pore morphology is considered. We explain the observed morphology using both crystallographic aspects and a model for the semiconductor/electrolyte interface based on the space charge approximation in a similar manner as in a Schottky semiconductor/metal barrier. The average volume porosity is estimated using a charge transfer calculation and compared to the results of an analysis of cross-sectional SEM images.; In p-type 6H SiC, the formation of the porous structure is obtained under no illumination is found to be dependent on the wafer polarity. We observe a branched type of morphology when the C-face is etched. The porous structure is uniform through the whole porous layer. The pore wall thickness is found to correlate with the etching current density. No porous layer formed when the etching is done on the Si-face of p-type SiC.; The anodization of n-type GaN heteroepitaxially grown samples is also studied. Preliminary results show some biaxial stress relief determined by blue shift of the near bandedge photoluminescence after the anodization.; The four appendices contain the results of the work on: (1) optical lifetime measurements in low doped epitaxial layers of 4H SiC, (2) the low temperature photoluminescence studies of 15MeV Erbium implanted 4H and 6H SiC, (3) and the study of the near bandedge cathodoluminescence of AlN. |
