Stacked layers of In(Ga)As on GaAs(001) self-assembled quantum rings (QR) for laser application have been studied. Several samples with three stacked QR layers have been grown by molecular beam epitaxy with GaAs spacers from 1.5 to 14 nm. The optical and structural properties have been characterized by photoluminescence spectroscopy and by atomic force microscopy, respectively. For GaAs spacers larger that 6 nm, the stacked QR layers present similar properties to single QR layers. A semiconductor laser structure with three stacked layers of QR separated 10 nm in the active region has been grown. This spacer ensures well-developed rings with optical emission like that of a single layer. Laser diodes have been processed with 1-2 mm cavity lengths. The stimulated emission is multimodal, centred at 930 nm (77 K), with a threshold current density per QR layer of 69 A cm −2. In this work, it is demonstrated that stacking rings is possible, and that a broad area laser with three QR layers can be fabricated successfully.

In this work, we experimentally demonstrate magnetic modulation of mid-infrared (mid-IR) plasmon resonances in microantenna and hole-array metamaterial platforms made of Ni81Fe19/Au multilayers. The responsible mechanism is the magnetorefractive effect linked to the giant magnetoresistance (GMR) present in this system. Ni81Fe19/Au multilayers experience a modification in the electrical resistivity upon the application of a small magnetic field. This directly translates into a change in the optical constants of the multilayer, making it possible to magnetically modulate the plasmon resonances. Because GMR acts on conduction electrons, the optical modulation occurs in the low energy, mid-IR range, even being possible to extend it to the THz range. Electrodynamical calculations confirm the experimental observations. This approach improves by up to 2 orders of magnitude previous attempts for mid-IR magnetic modulation, is potentially ultrafast due to the characteristic spintronics dynamics, and establishes a roadmap for spintronically controlled devices in the whole mid-IR to THz band.

Ultraviolet emission efficiency enhancement of a-plane AlGaN/GaN multiple-quantum-wells with increasing quantum well thickness Appl. Phys. Lett. 100, 261901 (2012) Photoexcited carrier dynamics in AlInN/GaN heterostructures Appl. Phys. Lett. 100, 242104 (2012) Photoluminescence recovery by in-situ exposure of plasma-damaged n-GaN to atomic hydrogen at room temperature AIP Advances 2, 022149 (2012) On conversion of luminescence into absorption and the van Roosbroeck-Shockley relation Appl. Phys. Lett. 100, 222103 (2012) Nature of optical transitions involving cation vacancies and complexes in AlN and AlGaN Appl. Phys. Lett. 100, 221107 (2012) Additional information on J. Appl. Phys. Dependence on the excitation power and temperature of the photoluminescence emission of GaAs quantum well laser structures using GaAs/AlAs superlattices in the waveguide is reported. The effects related to a quality reduction due to the presence of a thick ternary AlGaAs cladding layer in the bottom of the laser structure were elucidated by comparing to the photoluminescence of a similar waveguide structure, except for the AlGaAs bottom layer. The excitation power dependence shows the strong excitonic origin of the light emission in the temperature range 4-300 K in both structures. Carrier transport mechanisms through the superlattices is analyzed from the evolution of the photoluminescence of the quantum well and the superlattice confining layers; a structure dependent transparency temperature is defined, at which transport changes from tunneling assisted to extended minibands regime. The value of this parameter depends on the localized states in the superlattice minibands, caused by interface roughness.

Abstract:The spontaneous emission rate and Purcell factor of selfassembled quantum wires embedded in photonic crystal micro-cavities are measured at 80 K by using micro-photoluminescence, under transient and steady state excitation conditions. The Purcell factors fall in the range 1.1 -2 despite the theoretical prediction of ≈15.5 for the figure of merit. We explain this difference by introducing a polarization dependence on the cavity orientation, parallel or perpendicular with respect to the wire axis, plus spectral and spatial detuning factors for the emitters and the cavity modes, taking in account the finite size of the quantum wires. ©2012 Optical Society of America