Formation and characterization of columnar porous silicon carbide fabricated by photo-electrochemical etching

This thesis concentrates on the physical aspects of the columnar pore formation in the Si-face (0001), C-face (0001), and a-face (11 2 0) n-type 4H and 6H SiC using photoelectrochemical etching. The electrochemical etching of p-type 4H and 6H crystals is also illustrated.;In Si-face n-type 4H and 6H SiC, the columnar pores are about one mum in diameter. The formed porous layer is of high porosity and thus fragile. The formation of a hybrid partial columnar porous structure to improve the mechanical strength for possible biomedical applications is discussed in detail.;Nano-columnar pores are successfully fabricated in C-face n-type 4H and 6H SiC. The self-organized columnar pores have diameters of about 20+/-5 nm. The average interpore spacing from center to center is between 40-60 nm. The porous layer can be as thick as 200 mum. Systematic studies on the experimental control parameters, such as voltage, temperature, surface roughness, HF concentration, and doping concentration, have been performed and explained in detail. The charge transfer mechanisms are discussed extensively. The mechanisms that determine the observed pore diameter, interpore spacing, and columnar pore shape have been explored. The pore pattern formation simulation using a diffusion limited aggregation model and an impedance analysis using an equivalent circuit are discussed.;The 20 nm diameter nano-columnar pore formation has also been observed on the a-face n-type 6H SiC. The experimental observations are recorded and the voltage effects on the formed porous structure are discussed. The mechanism of the possible columnar pores formation in a-face SiC is discussed.;In the electrochemical etching of p-type 4H and 6H SiC, the electrochemical polishing, porosity dependence on the current density, porosity variation during the etching and doping effects on the porous formation are discussed. This work also contains useful information about how to electro-polish SiC and how to obtain low porosity p-type porous SiC.;The five appendices contain detailed information about: (1) my publication list, (2) the fabrication of porous SiC, (3) the fabrication of porous Al 2O3, (4) operation/maintenance of the mechanical polishing of SiC, and (5) operation/maintenance of the Varian 936-60 Leak Detector and the E-beam Evaporator.