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Dilute-nitride GaAsNx epilayers were grown on GaAs (001) substrates at temperatures of ∼450 °C using a radio-frequency plasma-assisted molecular/chemical beam exitaxy system. The concentration of nitrogen incorporated into the films was varied in the range between 0.01 and 0.04. High-resolution electron microscopy was used to determine the cross-sectional morphology of the epilayers, and Z-contrast imaging showed that the incorporated nitrogen was primarily interstitial. {110}-oriented microcracks, which resulted in strain relaxation, were observed in the sample with the highest N concentration ([N] ∼ 3.7%). Additionally, Z-contrast imaging indicated the formation of a thin, high-N quantum-well-like layer associated with initial ignition of the N-plasma. Significant N contamination of the GaAs barrier layers was observed in all samples, and could severely affect the carrier extraction and transport properties in future targeted devices. Dilute-nitride quantum-well-based photovoltaic solar cells were fabricated having a band-gap energy of 1.19 eV, which was attributed to the dilute-nitride layer.

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The efficiency of existing In(Al)GaP/GaAs/Ge multijunction solar cell can be further increased by the introduction of a 4 th junction with a band-gap in the range of 1 eV in between GaAs and Ge junctions. Dilute nitride (Ga(In)AsN) multi quantum wells (MQWs) inserted into the intrinsic region of a p-i-n GaAs are good candidates for this purpose. In this work, modeling has been done to estimate the feasibility of this structure. The result shows that the MQW 1 eV subcells could produce photocurrents greater than 18 mA/cm -2 when operating in a tandem configuration behind a GaAs solar cell and thus can support 4junction solar cells with 1 sun AM0 conversion efficiencies in the 40% range.

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