Investigations of 1.55-μm GaInNAs/GaAs heterostructures by optical spectroscopy

Dilute nitride semiconductors are a topic of major current research interest owing to the novel physics induced by the incorporation of N in small percentages of composition. Related research has been further motivated by the favourable characteristics for device applications of the resultant materials, particularly represented by GaInNAs quaternary compounds as active materials in the 1.3-1.6 μm wavelength range. Whilst 1.3-μm GaInNAs/GaAs materials and devices are now reaching a level of maturity, the extension of these structures to around 1.55 μm is still in its infancy. The authors report optical studies of 1.55-μm GaInNAs/GaAs heterostructures of varying characteristics, all grown by molecular beam epitaxy. As the addition of N complicates the local structure and optical properties in this material system, the PL mechanisms are clarified by detailed PL excitation (PLE) spectra. Whereas all the measured samples exhibit strong PL at room temperature, the electronic structure is quite different between samples grown under different conditions. Some demonstrate clearly standard 2-D quantum well (QW) electronic states and some demonstrate evidence of phase-separated quantum-dot-like (QD) structures.