Composition dependence of the band gap energy of In(x)Ga(1-x)N layers on GaN(x < = 0.15) grown by metal-organic chemical vapor deposition

We report on the composition dependence of the band gap energy of strained hexagonal In(x),Ga(1-x)N layers on GaN with x<=0.15, grown by metal-organic chemical vapor deposition on sapphire substrates. The composition of the (InGa)N was determined by secondary ion mass spectroscopy. High-resolution X-ray diffraction measurements confirmed that the (InGa)N layers with typical thicknesses of 30 nm are pseudomorphically strained to the in-plane lattice parameter of the underlying GaN. Room-temperature photoreflection spectroscopy and spectroscopic ellipsometry were used to determine the (InGa)N band gap energy. The composition dependence of the band gap energy of the strained (InGa)N layers was found to be given by EG(x)=3.43-3.28x(x) (eV) for x<=0.15. When correcting for the strain induced shift of the fundamental energy gap, a bowing parameter of 3.2 eV was obtained for the composition dependence of the gap energy of unstrained (InGa)N.