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.

Measurements of the Thermal Resistivity of InAlAs, InGaAs, and InAlAs/InGaAs Superlattices.

Thermal management efforts in nanoscale devices must consider both the thermal properties of the constituent materials and the interfaces connecting them. It is currently unclear whether alloy/alloy semiconductor superlattices such as InAlAs/InGaAs have lower thermal conductivities than their constituent alloys. We report measurements of the crossplane thermal resistivity of InAlAs/InGaAs superlattices at room temperature, showing that the superlattice resistivities are larger by a factor of 1.2-1.6 than that of the constituent bulk materials, depending on the strain state and composition. We show that the additional resistance present in these superlattices can be tuned by a factor of 2.5 by altering the lattice mismatch and thereby the phonon-mode mismatch at the interfaces, a principle that is commonly assumed for superlattices but has not been experimentally verified without adding new elements to the layers. We find that the additional resistance in superlattices does not increase significantly when the layer thickness is decreased from 4 to 2 nm. We also report measurements of 250-1000 nm thick films of undoped InGaAs and InAlAs lattice-matched to InP substrates, for there is no published thermal conductivity value for the latter, and we find it to be 2.24 ± 0.09 at 22 °C, which is ∼2.7 times smaller than the widely used estimates.

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.

Simple design of an edge-emitting diode laser for preventing spatial multimoding via thermal lensing.

The parameters of a diode-laser structure composed of a pair of built-in high-index regions for providing stable, single-spatial-mode operation to high cw powers are numerically found. A three-dimensional numerical code has been implemented that takes into account carrier diffusion in the quantum well and thermal lensing. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, higher-order optical modes on a "frozen background" are computed via the Arnoldi algorithm. Then, for a 6-µm-wide low-index core and 2-3-mm-long devices, stable single-mode operation up to multiwatt-level (2-3 W) cw output power is predicted.