An intrinsic property of quaternary alloys A 1Ϫy B y C 1Ϫx D x (xϷ1 -3 %) with D being an isovalent trap is reported: a set of discrete band gaps occurs due to substitution of the isovalent trap D on sites with different nearest-neighbor environments. Exemplary, this phenomenon is demonstrated for ͑Ga,In͒͑N,As͒ by experiment and explained by tight-binding supercell calculations. The band gap of this nitrogen-poor alloy is blueshifted by simply moving the nitrogen isovalent traps from Ga-ligand rich sites to In-ligand rich sites, without changing the alloy composition.

GaN x As 1−x samples with x<3% grown by metalorganic vapor phase epitaxy were studied by low-temperature photoluminescence under hydrostatic pressure and photomodulated reflectance spectroscopy. The transformation from N acting as an isoelectronic impurity to N-induced band formation takes place at x≈0.2%. The N level does not shift with respect to the valence band edge of GaNxAs1−x. Concentration as well as hydrostatic-pressure dependence of the GaNxAs1−x bands can be described by a three band kp description of the conduction band state E− and E+ and the valence band at k=0. The model parameters for T<20 and T=300 K were determined by fitting the model to the experimental data. Modeling the linewidth of the E− transition by combining the kp model and ion statistics leads to the conclusion that the electron-hole pairs are strongly localized.

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Compressively strained Ga(NAsP) multi-quantum-well heterostructures with As concentration above 85% have been grown pseudomorphically on GaP substrates by metal organic vapor phase epitaxy. Detailed structural analysis applying high-resolution x-ray diffraction proves the high crystalline perfection of the samples. Optical spectroscopy appyling photoluminescence and excitation spectroscopy verify the direct-band-gap characteristic of this novel material system. The comparison of the experimental data with elemental calculations via the band anticrossing model demonstrates that the formation of direct band structure can be understood by the strong bowing of the band gap energy typical for diluted III-V nitrides.

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