Interdiffusion has been investigated in molecular-beam epitaxially (MBE)-grown, highly strained In0.35Ga0.65As/GaAs multiple quantum well (MQW) structures. Thermal intermixing and impurity-free interdiffusion (IFID) was induced via rapid thermal annealing (RTA) at temperatures between 700 and 950 °C using GaAs proximity caps and electron-beam evaporated SiO2 cap layers, respectively. Both reduced photoluminescence (PL) linewidths and increased PL intensities were observed following interdiffusion-induced band-gap shifts ranging from 6 to 220 meV. PL microscopy (PLM) investigations were utilized to study the onset of strain relaxation due to dislocation generation. Two types of line defects were found in the proximity-cap annealed samples, depending on the annealing temperature and the number of QWs: misfit dislocations with the dislocation lines parallel to 〈110〉 directions and 〈100〉-oriented line defects. No dislocations were observed in the SiO2-cap annealed samples over the entire temperature range investigated here. Resonant Raman scattering measurements of the 1LO/2LO phonon intensity ratio were used for a semiquantitative assessment of the total defect densities, including point defects (PDs). Whereas increasing PD densities and the formation of line defects were observed in the proximity-capped samples as the annealing temperature was increased, no deterioration of the structural quality due to an increased PD density was observed in the case of the SiO2-cap annealed samples.

Growth of high-quality GaAs/AlAs Bragg mirrors on patterned InP-based quantum well mesa structuresMirror facets of broad area AlGaAs SQW 808 nm lasers with fast degradation of the output power have been investigated by photoluminescence microscopy ͑PLM͒, electroluminescence microscopy, and micro-photocurrent spectroscopy techniques. Over 2000 images of the photoluminescent light emitted from the facets of approximately 20 degraded laser bars have been made. Repeating patterns associated with the degradation have been noted and classified. Degraded lasers have dark lines on the mirror facet surface which are inclined from the epitaxial plane by 55°. Pairs of such lines often form V-shaped patterns. The orientation of the observed features suggest they are planar or line defects lying the the ͕111͖ crystallographic planes. The defects demonstrate a reduction in the lifetime of nonequilibrium electron-hole pairs and increased density of states in the forbidden gap of the active region of the laser structure, and are directly related to laser failure. Observations of the evolution in size and contrast of PLM patterns with ageing suggest the defects were initially created in the active region side of the laser structures during crystal growth or during the mounting procedure, and later propagate in the ͕111͖ planes, stimulated by the lasing action. We interpret the V formation to be a way to relax a compressive strain in the epitaxial plane. A dislocation on the ͕111͖ planes could actually translate the portion of the crystal bounded by the V upwards ͑away from the mounting of the crystal͒, in response to compressive strain.

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An ultra-compact, ultra-broadband vertical coupler for dense photonic integrated circuits is reported with a 1.07 � 0.62 μm 2 wavelength-scale footprint. This hybrid plasmonicphotonic coupler uses a unique two-plane plasmonic nanoantenna array on a siliconon-insulator waveguide. The in-and out-of-plane interference of the multipole moments and dual-feed nanoantennas results in efficient, unidirectional coupling. Finiteelement simulations show that, for a 0.8 μm diameter Gaussian beam, the maximum coupling efficiency (CE) is −3.4 dB across the telecommunication C-, L-and U-bands with a 3-dB bandwidth of 230 nm. The CE is > 9 dB higher than recently reported ultra-compact plasmonic couplers. The maximum directivity and polarisation extinction ratio across the C-to U-bands are 9.2 and 24.1 dB, respectively. Finally, as an out-coupler, it has a vertical directivity of >8.5 dB, enabling its use for vertical optical interconnects between two vertically separated circuits.

We study the influence of lateral carrier diffusion on the properties of In(0.35)Ga(0.65)As/GaAs multiple quantum well lasers by comparing theoretical and experimental results. A model including the carrier diffusion terms into the rate equations has been used to calculate the dc and small-signal lateral profiles for both unconfined and confined carriers in mesa waveguide devices. The theoretical results were compared with experimental results of the frequency dependence of the subthreshold electrical impedance and small-signal spontaneous emission, and with the measured threshold currents for lasers with different mesa widths. The comparison yielded an estimation for the nonradiative and radiative recombination coefficients, the ambipolar diffusion constant, and the external surface recombination velocity