We have improved fabrication processes of periodically inverted AlGaAs waveguides for highly efficient quasi-phase-matched wavelength conversion. In order to reduce propagation losses in waveguiding devices fabricated based on sublattice reversal epitaxy, we have introduced template planarization by chemical mechanical polishing and low-temperature regrowth technique. Corrugations at the core/ clad interface and the propagation loss at 1.55 mm has been reduced to 40 nm and 9 dB/cm, respectively. First-order quasi-phase-matched second-harmonic generation was demonstrated at 1.55 mm fundamental wavelength with a 1.47-mm-long device. Obtained internal conversion efficiency is 2.2%/W which is one order of magnitude lower than the theoretical value for an ideal lossless waveguide. A significant increase in the conversion efficiency is expected with a redesign of the device and further optimization of the fabrication processes. #

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We report very long intrinsic radiative recombination lifetime τrad in type II InAs quantum dots embedded in GaAs1−xSbx. The dependence of photoluminescence (PL) decay time τPL on both the Sb composition (x = 0–0.18) and excitation intensity (38–460 mW/cm2) was systematically investigated by time-resolved PL measurements with a time-correlated single-photon counting method. All PL decay curves exhibited non-exponential profiles, and τPL was strongly dependent on the excitation intensity. These properties were well explained by solving rate equations of carrier density with neglecting nonradiative process, in which τrad is inversely proportional to carrier density. The 18% Sb sample exhibited a τPL of over 100 ns under weak excitation, which is longer than twice the previously reported values. We evaluated the value of τrad in InAs/GaAs1−xSbx QDs relative to that in type I InAs/GaAs QDs based on an effective mass approximation and found that the observed extremely long τPL corresponds to τrad.

To realize highly efficient intermediate-band solar cells (IB-SCs), a long lifetime of photo-generated carriers in the IB is essential. We propose a new concept for this purpose based on IB absorbers using quantum-dots (QDs). By inserting potential walls between QDs and barriers that form a type II band alignment, electrons in the IB and holes in the valence band are farther separated compared to those in a conventional type II QD material, leading to significant reduction of radiative recombination. We designed a concrete structure using InAs QDs, GaAs 1Àx Sb x barriers, and GaAs walls to find the suitable GaAs wall thickness and Sb content being 2 nm and x ¼ 0.18, respectively, and demonstrated a lifetime of electrons excited to the IB as long as 220 ns. V C 2012 American Institute of Physics. [http://dx.

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