The wide bandgap semiconductors Silicon carbide and gallium nitride have been studied by Raman scattering, photoluminescense, and infrared absorption. Raman scattering studies determined crystalline quality and polytype of bulk and thin film samples at room temperature to detected and/or identify impurity centers and structure related defects and their role on the electronic properties of the materiais. Infrared absorption spectroscpopy was used to measure the binding enrgy of donors and their concentration.