Reduced auger recombination in mid-infrared semiconductor lasers

A quantum-design approach to reduce the Auger losses in two micron InGaSb type-I quantum well edge-emitting lasers is reported. Experimentally realized structures show a 3X reduction in the threshold, which results in 4.6 lower Auger current loss at room temperature. This is equivalent to a carrier lifetime improvement of 5.7 and represents about a 19-fold reduction in the equivalent “Auger coefficient.

Influence of microscopic many-body scattering on multi-wavelength VECSEL lasing

Non-equilibrium multi-wavelength operation of vertical external-cavity surface-emitting lasers (VECSELs) is investigated numerically using a coupled system of Maxwell semiconductor Bloch equations. The propagation of the electromagnetic field is modeled using Maxwell's equations, and the semiconductor Bloch equations simulate the optically active quantum wells. Microscopic many-body carrier-carrier and carrier-phonon scattering are treated at the level of second Born-Markov approximation, polarization dephasing with a characteristic rate, and carrier screening with the static Lindhard formula. At first, an initialization scheme is constructed to study multi-wavelength operation in a time-resolved VECSEL. Intracavity dual-wavelength THz stabilization is examined using longitudinal modes and an intracavity etalon. In the latter, anti-correlated noise is observed for THz generation and investigated.Air Force Office of Scientific Research [FA9550-17-1-0246]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Carrier dynamics in TMDCs for optical applications

Fully microscopic many-body models based on the Dirac-Bloch equations and quantum-Boltzmann type scattering equations are used to study the carrier dynamics in monolayer transition metal dichalcogenides (TMDCs) under conditions as typical for applications as lasers, diodes or saturable absorbers. The carrier-carrier scattering is shown to be happening on an ultra-fast few-femtosecond timescale for excitations high above the bandgap. Once the carriers have relaxed into quasi-equilibrium distributions near the bandgap, the scattering is slowed dramatically by phase-space filling and screening of the Coulomb interaction. Here, the scatterings and resulting dephasing of the optical polarizations happen on a 100fs timescale and lead to similar broadenings as found in conventional III-V semiconductor materials. Also like the case in III-V materials, the carrier phonon scattering times are found to be in the picosecond range. The scatterings are shown to allow for gain spectra as needed for good lasing operation. It is shown that the weak interaction between the two bands associated with the two different sub-lattices can potentially allow for simultaneous lasing at two different frequencies. Strong absorption and ultrafast carrier relaxation could allow for TMDCs to be used in saturable absorption applications.Air Force Office of Scientific Research [FA9550-17-1-0246]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Extension of the LDA-1/2 method to the material class of bismuth containing III-V semiconductors

The LDA-1/2 method is employed in density functional theory calculations for the electronic structure of III-V dilute bismide systems. For the representative example of Ga(SbBi) with Bi concentrations below $10 \%$, it is shown that this method works very efficiently, especially due to its reasonably low demand on computer memory. The resulting bandstructure and wavefunctions are used to compute the interaction matrix elements that serve as input to microscopic calculations of the optical properties and intrinsic losses relevant for optoelectronic applications of dilute bismides

The WT1-like transcription factor Klumpfuss maintains lineage commitment of enterocyte progenitors in the Drosophila intestine

In adult epithelial stem cell lineages, the precise differentiation of daughter cells is critical to maintain tissue homeostasis. Notch signaling controls the choice between absorptive and entero-endocrine cell differentiation in both the mammalian small intestine and the Drosophila midgut, yet how Notch promotes lineage restriction remains unclear. Here, we describe a role for the transcription factor Klumpfuss (Klu) in restricting the fate of enteroblasts (EBs) in the Drosophila intestine. Klu is induced in Notch-positive EBs and its activity restricts cell fate towards the enterocyte (EC) lineage. Transcriptomics and DamID profiling show that Klu suppresses enteroendocrine (EE) fate by repressing the action of the proneural gene Scute, which is essential for EE differentiation. Loss of Klu results in differentiation of EBs into EE cells. Our findings provide mechanistic insight into how lineage commitment in progenitor cell differentiation can be ensured downstream of initial specification cues

Molecular Dynamics Study of the Nematic-Isotropic Interface

We present large-scale molecular dynamics simulations of a nematic-isotropic interface in a system of repulsive ellipsoidal molecules, focusing in particular on the capillary wave fluctuations of the interfacial position. The interface anchors the nematic phase in a planar way, i.e., the director aligns parallel to the interface. Capillary waves in the direction parallel and perpendicular to the director are considered separately. We find that the spectrum is anisotropic, the amplitudes of capillary waves being larger in the direction perpendicular to the director. In the long wavelength limit, however, the spectrum becomes isotropic and compares well with the predictions of a simple capillary wave theory.Comment: to appear in Phys. Rev.