The most interesting features of nitrides (GaN, AlN, InN, BN) and related alloys (InGaN and GaAsN) are presented considering their electronic, structural, optical and chemical properties. Ab-initio calculations of the band structure and total energy are performed by the linear muffin-tin orbital method (LMTO) method.
Studies of the energy band structures of nitrides, the pressure-induced phase transitions and lattice vibrations at high pressure indicate the role of specific features of the nitrogen atom and the role of the Ga-3d and In-4d semicore states.
The energy levels of native defects (vacancies and antisites) and impurities (C, Zn, Mg, O, Be), their formation energies and the effects of pressure on these properties are calculated. For the cation vacancies, which are the most stable native defects in n-type material, we compare their behavior in the nitrides and in GaAs, finding substantial differences in the pressure dependence of the defect level positions and formation energies. Comparing the substitutional impurities GaN:Mg and GaN:Be, we find differences in their high pressure behavior, in agreement with the high pressure measurements of the light emission performed on GaN:Be and GaN:Mg samples.
Observed pecularities of InGaN and GaAsN band structures are explained in terms of ab-initio calculations:
1. unusually strong decrease of the InGaN bandgap and its pressure coefficient when indium is incorporated is related to the dramatic change of the valence band shape caused by strong hybridization of In(p,d) and Ga(p,d) wave functions.
2. The introduction of small amounts of nitrogen modifies strongly the conduction bands in GaAsN. The lowest conduction band exhibits strong non-parabolicity, and the fundamental gap, E_g, decreases with x. The Γ, L and X states mix and form new low-energy states. Pressure affects the electronic properties of GaAsN, and it influences the electron effective masses and their dependence on x.

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1. Indium segregation in Al_1-xIn_xN investigated by photoluminescence under hydrostatic pressure
2. In-segregation induced anomalous behavior of band gap and its pressure coefficient in InAlN and InGaN. Theory and Experiment