Formation and Characterization of Columnar Porous SiC Fabricated by Photo-electrochemical Etching
The major part of this work concentrates on the details of the physical aspects of the columnar pore formation in the Si-face (0001), the C-face (000-1), and the a-face (11-20) of n-type 4H and 6H SiC samples 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 ¦Ìm 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 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 nm. The interpore spacing from center to center is between 40-60 nm depending on the etching conditions. The porous layer can be as thick as 200 ¦Ìm. The porosity of the porous structure is about 0.1. Systematic studies on the experimental control parameters, such as voltage, reaction temperature, surface roughness, HF concentration, and doping concentration, have been performed and are explained in detail. The formation mechanisms are discussed extensively based on crystallographic aspects, diffusion limited aggregation, impedance spectroscopy, voltammetry, equivalent circuits, and semiconductor/electrolyte interface (similar to a Schottky semiconductor/metal interface) electrochemistry.
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.
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.
The five appendices contain information about: (1) my publication list, (2) technical notes about the fabrication of porous SiC, (3) technical notes about the fabrication of porous Al2O3, (4) operation procedures and technical notes about the mechanical polishing of SiC, and (5) operation procedures and technical notes about the Varian 936-60 Leak Detector and the E-beam Evaporator in our laboratory.
Advisor:R.P. Devaty; J. Levy; R.M. Feenstra; W.J. Choyke; Y.Y. Goldschmidt
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication:06/13/2008