Electrically injected 1.64µm emitting In0.65Ga0.35As 3-QW laser diodes grown on mismatched substrates by MOVPE.

We report the characteristics of the strained In0.65Ga0.35As triple quantum well (QW) diode lasers grown by metalorganic vapor phase epitaxy (MOVPE) on lattice-mismatched substrates such as GaAs or Si, by utilizing InP metamorphic buffer layers (MBLs) in conjunction with InAs nanostructure-based dislocation filters. As the lattice-mismatch between the substrate and InP MBL increases, higher threshold current densities and lower slope efficiencies were observed, together with higher temperature sensitivities for the threshold current and slope efficiency. Structural analysis performed by both high-resolution X-ray diffraction (HR-XRD) and transmission electron microscopy indicates graded and/or rougher QW interfaces within the active region grown on the mismatched substrate, which accounts for the observed devices characteristics.

Annealing-induced precipitate formation behavior in MOVPE-grown GaAs1-x Bi x explored by atom probe tomography and HAADF-STEM.

The effects of a 45 min anneal at 800 °C on the physical properties and microstructure of a five-period GaAs1-x Bi x /GaAs1-y Bi y superlattice with y ≠ x were studied using room-temperature photoluminesence spectroscopy, high-resolution x-ray diffraction, high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM), and atom probe tomography (APT). The anneal resulted in a substantial increase of the photoluminesence intensity over that observed in the as-deposited sample, indicating annihilation of non-radiative recombination centers and stability of the superlattice structure during the anneal. However, some precipitation of Bi from the GaAs1-x Bi x also occurred. The characteristics of phase separation that occurred within these precipitates were investigated in detail by APT and HAADF-STEM. They indicate that the precipitation reaction involves formation of embedded nano-scale liquid droplets that can accelerate local Bi dissolution from the GaAs1-x Bi x matrix by moving through it. Preservation of nanometer scale sharp Bi concentration gradients in the growth direction suggested that very little solid state diffusion of Bi occurred during the anneal. The observed gradient in precipitate number density with distance from the sample surface further supports hypotheses of an enabling role of Ga vacancies in the precipitation process.

AlxGa1-xAs nested waveguide heterostructures for continuously phase-matched terahertz difference frequency generation.

We previously demonstrated a nested pair of single mode (pump/THz) waveguides which produced guided far-infrared (1.3 THz) light with a record power-normalized conversion efficiency of 1.3x10(-7) W(-1) by way of continuous phase matched difference frequency generation (DFG) [Opt. Express 16, 13296 (2008)]. Using the same numerical simulation tools we used to design and model this LiNbO(3)-based device, we show that a lattice-matched AlGaAs heterostructure, with its significantly lower absorption losses, can produce guided far-infrared light (3.5 THz) with a power-normalized conversion efficiency of 1.3 x 10(-5) W(-1) - some 100 times larger than achieved with the LiNbO(3) structure.

Degradation of Hole Transport Materials via Exciton-Driven Cyclization.

Organic light-emitting diode (OLED) displays have been an active and intense area of research for well over a decade and have now reached commercial success for displays from cell phones to large format televisions. A more thorough understanding of the many different potential degradation modes which cause OLED device failure will be necessary to develop the next generation of OLED materials, improve device lifetime, and to ultimately improve the cost vs performance ratio. Each of the different organic layers in an OLED device can be susceptible to unique decomposition pathways, however stability toward excitons is critical for emissive layer (EML) materials as well as any layer near the recombination zone. This study will specifically focus on degradation modes within the hole transport layer (HTL) with the goal being to identify the general decomposition paths occurring in an operating device and use this information to design new derivatives which can block these pathways. Through post-mortem analyses of several aged OLED devices, an apparently common intramolecular cyclization pathway has been identified that was not previously reported for arylamine-containing HTL materials and that operates parallel to but faster than the previously described fragmentation pathways.

Experimental demonstration of 1535-1555-nm simultaneous optical wavelength interchange with a nonlinear photonic crystal.

We present results of what is to our knowledge the first experimental demonstration of simultaneous optical wavelength interchange by use of a two-dimensional second-order nonlinear photonic crystal. Fabrication and performance parameters of a 1535-1555-nm wavelength interchange nonlinear photonic crystal fabricated in lithium niobate are discussed.