Low-temperature photoluminescence studies in epitaxially-grown GaAsN/InAs/GaAsN quantum-dot-in-well structures emitting at 1.31 μm

We report a single layer GaAsN/InAs/GaAsN quantum-dot-in-well (DWELL) structure with PL emission at 1.31μm important for applications in communication lasers. This extension has been achieved with a nitrogen composition of only 1.8% and QDs embedded within 1/6nm GaAsN which is higher compared to single layer QDs with GaAs and GaAsN capping layers as a result of confinement reduction on both sides of the QD energy levels. The structures remain as QDs till 800°C of annealing temperature alongwith a drastic enhancement in PL intensity as a result of annihilation of N-induced crystal defects which provide non-radiative recombination centers for carriers in the as-grown sample which is responsible for degraded luminescence. A typical highly asymmetric PL signature observed in dilute nitride structures is seen with a sharp cut-off at lower wavelengths and a large exponential tail at higher wavelengths in the as-grown and 650°C annealed samples. This is due to the presence of localized excitonic states extending into the bandgap close to the band edges. For higher annealing temperatures, this asymmetry disappears indicating an improvement in uniformity of nitrogen distribution and absence of localized states; which is also confirmed from a smaller blueshift in excitation intensity-dependent PL spectra of these samples. Well-resolved ground and first excited states in the PL spectrum of 700°C annealed sample indicates an improvement in QD confinement.