Date of Award

Summer 8-23-2010

Degree Type


Degree Name

Master of Science (MS)


Physics and Astronomy

First Advisor

Dr. Nikolaus Dietz

Second Advisor

Dr. Unil A. G. Perera

Third Advisor

Dr. Unil A. G. Perera

Fourth Advisor

Dr. Vadym Apalkov


Optical absorption spectroscopy has been applied to study properties such as the fundamental absorption edge and defect absorption centers of group III-nitride compound semiconductor epilayers. The investigation in this thesis focused on analyzing the band gap of indium-rich In1-xGaxN epilayers, which where grown by the high-pressure chemical vapor deposition (HPCVD) technique. Our results - together with literature data for gallium-rich In1-xGaxN alloys indicate that the shift of the fundamental band gap of In1-xGaxN with composition x can be described with a bowing parameter of b = 2.2eV. Temperature dependent transmission measurements show that the band gap variation with temperature follows a S-shape behavior for small gallium concentration and shifts towards a Varshni type behavior for a higher gallium concentrations. The S-shape behavior is attributed to nanoscale compositional fluctuations/clustering in the ternary alloy system. The thicknesses of the measured In1-xGaxN epilayers have been analyzed through multilayer stack model calculations of the transmission spectra. The free electron concentration in the In1-xGaxN epilayers has been obtained from simulations of infrared reflectance spectra.