Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Koshka, Yaroslav

Committee Member

Mazzola, Michael S.

Committee Member

Winton, Raymond S.

Committee Member

Kim, Seong-Gon

Date of Degree

5-1-2010

Document Type

Dissertation - Open Access

Major

Electrical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Electrical and Computer Engineering

Abstract

A novel process for low-temperature (LT) epitaxial growth of silicon carbide (SiC) by replacing the growth precursor propane with chloro-methane was recently developed at Mississippi State University. However, only limited information was available about the defects and impurity incorporation in the various types of epitaxial layers produced by this new method like blanket epitaxial layers, selectively grown epitaxial mesas, and highly doped epitaxial layers, prior to their comprehensive characterization in this work. Molten potassium hydroxide (KOH) etching, mechanical polishing and a variety of other characterizing techniques were used to delineate and identify the defects both in the epilayer and substrates. Under optimum growth conditions, the concentration of defects in the epitaxial layers was found to be less than that in the substrate, which established the good quality of the LT growth process. Defect concentrations, on selectively grown epitaxial layers, strongly depended on the crystallographic orientation of the mesa sidewall. The addition of HCl to the growth process, aimed at increasing the growth rate, caused a significant concentration of triangular defects (TDs) to be formed in the epitaxial layers. The TDs were traced down to the substrate by a combination of repeated polishing and molten KOH etching steps. The TDs were found not to originate from any substrate defects. Their origin was traced to polycrystalline silicon islands which form on the surface during growth and subsequently get evaporated away, which had made it impossible to detect them and suspect their influence on the TD generation prior to this work. The TDs were found to include single or multiple stacking faults bound by partial dislocations and, in some cases, inclusions of other SiC polytypes. Gradual degradation of the epitaxial morphology was found in heavily aluminum doped p+ layers, with an increase in the level of doping, followed by much steeper degradation when approaching the solubility limit of Al in 4H-SiC. Precipitates were the dominating defect at the highest levels of doping and were observed beyond a doping of 3.5x1020 cm-3. A dislocation generation model for heavily doped epitaxial layers was developed accounting for the stress in the lattice caused by Al doping.

URI

https://hdl.handle.net/11668/17278

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