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A key to the utilization of nitride-arsenides for long wavelength optoelectronic devices is obtaining low defect materials with long nonradiative lifetimes. Currently, these materials must be annealed to obtain device quality material. The likely defect responsible for the low luminescence efficiency is associated with excess nitrogen. Photoluminescence and capacitance–voltage measurements indicate the presence of a trap associated with excess nitrogen which decreases in concentration upon anneal. Our films are grown by elemental source molecular beam epitaxy and the background impurity concentration is low, thus we have investigated the role of crystalline defects. High resolution x-ray diffraction showed improved crystal quality after anneal. We observed that the lattice parameter does not decrease linearly with nitrogen concentration for levels of nitrogen above 2.9 mol % GaN. The fact that Vegard’s law is not observed, despite theoretical calculations that it should, indicates that nitrogen incorporates in locations other than the group V lattice sites. X-ray photoelectron spectroscopy revealed that nitrogen exists in two bonding configurations in not-annealed material: a Ga–N bond and another nitrogen complex in which N is less strongly bonded to gallium atoms. Annealing removes this second nitrogen complex. A combined nuclear reaction analysis and channeling technique showed that not annealed GaNAs contains a significant concentration of interstitial nitrogen that disappears upon anneal. We believe that this interstitial nitrogen is responsible for the deviation from Vegard’s law and the low luminescence efficiency of not annealed GaNAs and GaInNAs quantum wells.

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Capacitance–voltage measurements on metal-semiconductor contacts are used to examine depth-resolved electrical characteristics of GaAs/Ga(As, N)/GaAs heterostructures. The experimental depth profiles of the carrier concentration are compared with calculations based on self-consistent solutions of the Poisson equation. As-grown Ga(As, N) layers are p type, and hole concentrations of about 3×1016 cm−3 are observed for undoped Ga(As, N) layers with a GaN mole fraction of 3% and thicknesses below 80 nm. This hole concentration is stable during rapid thermal annealing. For a GaN mole fraction of about 3%, the valence band offset between GaAs and Ga(As, N) is found to be +(11±2) meV. The heterointerfaces are of type I. The dominant carrier depletion in as-grown heterostructures is due to donor-like defect levels, which are accumulated at the GaAs-on-Ga(As, N) interface. The amount of these interfacial defects rises remarkably in thicker Ga(As, N) layers, but can be completely removed by rapid thermal annealing after growth. By release spectroscopy, further hole traps with definite level energies are distinguished at the Ga(As, N)-on-GaAs interface, which are probably due to the specific GaAs growth conditions.

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