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Nitrogen incorporation in GaAsN epilayers grown by chemical beam epitaxy using a radio-frequency (rf) plasma source as nitrogen precursor was studied as a function of growth conditions. For higher growth temperatures (∼460°C), only higher rf power values yield significant incorporation of nitrogen. The nitrogen incorporation exhibits two behaviors with the growth rate: metal-organic-chemical-vapor-deposition and molecular-beam-epitaxy like behaviors at low and high growth rate, respectively. The highest nitrogen compositions are obtained at rates of about 1 μm/h. Despite a significant reduction of the N incorporation with increasing growth temperature, the optimization of the growth conditions allowed us to reach nitrogen concentrations up to 7.1% for samples fabricated at 460 °C. Films with higher nitrogen content exhibit low-temperature luminescence at energies higher than those predicted using the band-anticrossing model and an extrapolation of the literature data for smaller N composition.

The authors present preliminary data for a set of GaAsN∕GaAs multiquantum well (MQW) solar cells, grown by radio-frequency (rf) nitrogen plasma-assisted chemical beam epitaxy. The spectral response of this preliminary set of devices extends well below the GaAs band gap, while exhibiting remarkably high photoconversion strength that exceeds that of other MQW-based solar cells with comparable band gaps (1.0–1.2eV). This behavior is consistent with the enhancement of the electron effective mass in III-V dilute nitrides. Although the output current is similar to that of conventional GaInAsN solar cells, the output voltage is significantly higher when compared to that of bulk solar cells of similar wavelengths. The spectral response of as-grown devices is characterized by a deep valley around 1.37–1.4eV, that could be attributed to N contamination of the GaAs barriers. Rapid thermal annealing improves significantly the spectral response in the vicinity of this valley.

The interaction of a typical gas-source molecular-beam epitaxy (GSMBE) environment with a radio-frequency (RF) nitrogen plasma source is investigated. In particular, a real-time in situ analysis of the evolution of the emission spectrum of an RF nitrogen plasma source, under high partial pressures of hydrogen (∼10−5Torr), is presented. Hydrogen, emanating from the decomposition of hydride precursors in GSMBE, results in the appearance of a sharp emission peak at the region of 656nm in the plasma spectrum, suggesting the generation of atomic hydrogen species in the nitrogen plasma cavity. The intensity of this peak is used for a qualitative evaluation of this interaction and its evolution as a function of the RF nitrogen plasma source conditions is investigated.

Photoluminescence and absorption spectroscopy experiments were performed on as grown and thermally annealed GaAs1-xNx with nitrogen content in the range of 0.75–7.1%. At low temperature, the photoluminescence spectra exhibits two set of features: (i) a relatively broad peak at low energy and near to the vicinity of the predicted band gaps and (ii) a sharp excitonic feature at higher energy (about 100 meV for x>4%). Post growth thermal annealing processes systematically favor stronger excitonic emissions, and a notable intensity reduction of the deeper (defect related) luminescence. The low temperature binding energy of the higher energy excitonic peak is found to be consistent with the increase of the electronic effective masses. A careful examination of the data obtained in this work suggests that for higher nitrogen content (x>4%), the fundamental band gap of GaAsN is located at significantly higher energies than those commonly accepted for these alloys.