Reflectivity investigations as a method for characterizing group III nitride films

A highly sensitive method for characterizing heteroepitaxial group III nitride films on various substrates is developed on the basis of reflectivity studies below and just above the fundamental absorption edge. By analyzing the envelopes of the reflectivity spectrum, the influence of a buffer layer, and/or a nonabrupt substrate/film interface is verified, the refractive index of the active layer can be calculated independently of both the active layer thickness and the interface properties, and finally, qualitative conclusions about the interface properties are deduced. On this basis a suitable model for data fitting is established which contains only a small number of adjusted parameters. Moreover, the correlation between the refractive index and the thickness of the active layer is removed. From the fit, the energy dispersion of the refractive index and the thickness for both the active layer and the interlayers are obtained. The ability and high accuracy of the method is demonstrated by applying it to ...