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.

Capacitance spectroscopy is used to examine the compositional dependence of deep levels in Si-doped Ga(As,N) layers grown on GaAs. We find two predominant electron traps at about 0.80 and 1.1 eV above the valence band edge EV, which do not depend on composition. For N contents above 0.1% N, the concentration of the acceptor-like gap level at EV+1.1 eV strongly increases and leads to a distinct reduction of the donor doping efficiency in Ga(As,N) layers. Based on theoretical prediction, this electron trap is tentatively associated with a split interstitial defect containing a nitrogen and an arsenic atom on the same As lattice site [(AsN)As]. The trap at EV+0.80 eV likely corresponds to nitrogen dimers, i.e., two N atoms on a single As site [(NN)As]. When approaching the critical layer thickness, this electron trap is increasingly generated during growth. The dimer defect can be removed by rapid thermal annealing at 720 °C after growth, in contrast to the stable bulk level at EV+1.1 eV. By the formation of both N-related defects, the tensile strain in Ga(As,N) is reduced.

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.

Deep-level defects in p-type GaAs/Ga(As,N)/GaAs heterostructures grown by molecular beam epitaxy are investigated by deep-level transient Fourier spectroscopy. Depth-resolved distributions of hole traps are measured in as-grown and annealed heterojunctions in order to identify the defects, which lead to the degradation of the Ga(As,N) properties. Four defects are recognized in the heterostructures studied. Two dominant hole traps are found in Ga(As,N) at energies of about 0.35 and 0.45 eV above the valence band edge. These midgap levels originate from copper- and iron-related defects, the formation of which is connected with operation of the nitrogen plasma cell during Ga(As,N) growth. Both traps, which are removed by annealing, are discussed as the possible nonradiative centers that deteriorate the optical properties. Two other hole traps of intrinsic origin are related to the GaAs growth conditions close to the Ga(As,N)-on-GaAs interface, where the GaAs growth is affected by the nitrogen plasma despite a closed shutter. As far as electronic levels in the lower half of the band gap are concerned, the Ga(As,N) layers and GaAs-on-Ga(As,N) interfaces become practically defect free after rapid thermal annealing.

Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al 0.2 Ga 0.8 N / GaN interface and the rapid thermal annealing effect Deep levels in the upper half of the band gap of strained Ga͑As,N͒ with a GaN mole fraction of 3% are examined by deep-level transient Fourier spectroscopy on GaAs/Ga͑As,N͒/GaAs heterojunctions grown by molecular-beam epitaxy. In as-grown structures, we find a dominant electron trap at 0.25 eV below the conduction bandedge with a concentration above 10 17 cm Ϫ3 . Its capture cross section of about 10 Ϫ17 cm 2 for electrons is too small for an efficient nonradiative recombination center in Ga͑As,N͒. According to theoretical predictions, this level is most likely connected with a nitrogen-split interstitial defect (N-N) As . The giant concentration of this trap can be strongly reduced by rapid thermal annealing.