Group III-nitride based blue emitters

(AlGaIn)N-based heterostructures are of considerable current interest for the realization of short-wave length light-emitting semiconductor devices, covering the UV- to-blue spectral region. Recent advances in group Ill-nitride layer growth using MBE and, in particular, MOCVD allow the preparation of high-quality n- and p-type conducting GaN layers as well as GaN/(AlGa)N/(InGa)N hetero- and quantumstructures, in spite of the lack of lattice matched substrates. This progress in growth technology enabled the realization, and commercialization, of high-efficiency blue light emitting diodes and the demonstration of a diode laser emitting in the violet spectral range. Despite this tremendous technological progress, important questions regarding basic material properties and growth related issues remain yet to be answered. In the present paper we shall discuss the effect of GaN surface termination on layer quality and surface morphology, the mechanisms limiting the maximum obtainable hole concentration in GaN:Mg, and the effect of compositional inhomogeneity in low In-content (InGa)N on the photoluminescence, reflection, and dielectric function spectrum.