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Predictions of deep levels associated with N vacancies in AlxGa1−xN as functions of alloy composition x explain both (i) the dramatic change from naturally n‐type to semi‐insulating behavior (for x=xc≂0.5) in terms of a shallow‐deep transition for the vacancy’s T2 level, and (ii) the major photoluminescence feature in terms of recombination from the vacancy’s A1 deep level. Extrinisic photoluminescence data for Zn‐doped AlxGa1−xN are interpreted in terms of a transition from the conduction band to a T2‐symmetric deep level in the lower part of the gap. This level is associated with antisite Zn on a N site, ZnN.

A simple, analytical, semiempirical model is presented for the optical constants of AlxGa1−xAs including the index of refraction. The model is tailored to the energy range of 1.0–3.0 eV, the operating range for many AlxGa1−xAs‐based devices and incorporates the important electronic transitions in the solid which affect light propagation and absorption. The parameters of the model are simple functions of composition allowing for ready computation of any of the optical constants, n, k, α, e1, or e2, for any energy E (or wavelength λ) of light between 1.0 and 3.0 eV (400–1200 nm) and any composition x.

Based on the idea of a zincblende‐diamond structural phase transition, we predict that metastable, crystalline, substitutional alloys of (InP)1−xGe2x should exhibit significantly smaller fundamental band gaps than has been expected for random alloys of InP and Ge, and hence may be candidates for materials with gaps ≂10 μm.