The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.

We present ab initio calculations of the electronic structure and the optical properties of In x Ga 1Àx N. They are completed by studies of the strain influence on the alloys. The results are critically discussed in the light of recent experiments. We find an energy gap of InN < 1 eV and a nonparabolic absorption edge. The strong variation of the alloy gap with the In molar fraction is described by a compositiondependent bowing parameter. The tendency of spinodal decomposition is suppressed by biaxial strain. Its extent depends on the realization of strain accommodation.

Hexagonal and cubic GaN layers are grown on (001) GaAs substrates by means of molecular beam epitaxy. First order Raman spectra are taken from these layers at various incident laser wavelengths and temperatures. The T2 transverse-optical (TO) and longitudinal-optical (LO) frequencies of cubic GaN are determined, as well as the A1 TO and LO, E1 TO, and E2 frequencies of hexagonal GaN. The T2 TO frequency of cubic GaN lies between the A1 and E1 TO frequencies of hexagonal GaN as one expects comparing the lattice dynamics of zincblende and wurtzite type crystals. The T2 TO frequency is close to the calculated value but disagrees with a recently reported experimental value. For the hexagonal layer, all frequencies are close to those previously measured. A broad Raman structure below the A1 LO peak is interpreted in terms of a disturbed long range order of the hexagonal layer.

First-principles total energy calculations, combined with a generalized quasichemical approach to disorder and compositional effects, are used to obtain the lattice parameter and the energy band gap of cubic AlxGayIn1−x−yN quaternary alloys. It is found that the lattice parameter a(x,y) fulfills a Vegard’s-like law; that is, it shows a linear dependence on the alloy contents x and y. The range of compositions for which the alloy is lattice-matched to GaN is obtained. The energy band gap Eg(x,y) of the quaternary alloy deviates from a planar behavior displaying a two-dimensional gap bowing in the x–y plane. Analytical expressions that fit the calculated a(x,y) and Eg(x,y) surfaces are derived in order to provide ready access to the lattice parameter and energy band gap of the alloy for the entire range of compositions. The results are compared with data for the wurtzite phase alloys.

High efficiency green, yellow, and amber emission from InGaN/GaN dot-in-a-wire heterostructures on Si (111) Appl. Phys. Lett. 96, 013106 (2010); 10.1063/1.3284660Exciton localization and quantum efficiency-A comparative cathodoluminescence study of (In,Ga)N/GaN and GaN/(Al,Ga)N quantum wells