Properties of cubic (In,Ga)N grown by molecular beam epitaxy

We discuss the growth and characterization of thick (>100 nm) cubic (In,Ga)N/GaN heterostructures on GaAs. The interpretation of optical experiments, which is in the main focus of the paper, is found to be impeded by two phenomena. First of all, the emission from (In,Ga)N is known to originate from localized states lower in energy than the actual band gap. By combining reflectance and transmittance spectroscopy, the absorption coefficient can be determined and thus principally the band gap. However, the high density of localized states may result in a quasi-continuous density of states, such that a band edge in the conventional sense is neither measurable nor definable. Second, independent measurements for determining the composition of the (In,Ga)N layer yield an average composition while the compositional distribution, originating from the bulk immiscibility of (In,Ga)N, is difficult to obtain.