Defect characterization of InAs/InGaAs quantum dot p-i-n photodetector grown on GaAs-on-V-grooved-Si substrate

The performance of semiconductor devices on silicon can be severely degraded by the presence of dislocations incurred during heteroepitaxial growth. Here, the physics of the defect mechanisms, characterization of epitaxial structures, and device properties of waveguide photodetectors (PDs) epitaxially grown on (001) Si are presented. A special GaAs-on-V-grooved-Si template was prepared by combining the aspect ratio trapping effects, superlattice cyclic, and strain-balancing layer stacks. A high quality of buffer structure was characterized by atomic force microscopy (AFM) and electron channeling contrast imaging (ECCI) results. An ultralow dark current density of 3.5 × 10–7A/cm2 at 300 K was measured under −1 V. That is 40× smaller than the best reported value of epitaxially grown InAs/GaAs quantum dot photodetector structure on GaP/Si substrate. Low frequency noise spectroscopy was used to characterize the generation and recombination related deep levels. A trap with an activation energy of 0.4 eV was identified, which is near the middle bandgap. With low frequency noise spectroscopy along with the current–voltage and capacitance–voltage characterizations, the recombination lifetime of 27 μs and trap density of 5.4 × 1012 cm–3 were estimated

1.3 μm submilliamp threshold quantum dot micro-lasers on Si

As a promising integration platform, silicon photonics need on-chip laser sources that dramatically improve capability, while trimming size and power dissipation in a cost-effective way for volume manufacturability. Currently, direct heteroepitaxial growth of III–V laser structures on Si using quantum dots as the active region is a vibrant field of research, with the potential to demonstrate low-cost, high-yield, long-lifetime, and high-temperature devices. Ongoing work is being conducted to reduce the power consumption, maximize the operating temperature, and switch from miscut Si substrates toward the so-called exact (001) Si substrates that are standard in microelectronics fabrication. Here, we demonstrate record-small electrically pumped micro-lasers epitaxially grown on industry standard (001) silicon substrates. Continuous-wave lasing up to 100°C was demonstrated at 1.3 μm communication wavelength. A submilliamp threshold of 0.6 mA was achieved for a micro-laser with a radius of 5 μm. The thresholds and footprints are orders of magnitude smaller than those previously reported lasers epitaxially grown on Si

Glycosylation Is Vital for Industrial Performance of Hyperactive Cellulases

In the terrestrial biosphere, biomass deconstruction is conducted by microbes employing a variety of complementary strategies, many of which remain to be discovered. Moreover, the biofuels industry seeks more efficient (and less costly) cellulase formulations upon which to launch the nascent sustainable bioenergy economy. The glycan decoration of fungal cellulases has been shown to protect these enzymes from protease action and to enhance binding to cellulose. We show here that thermal tolerant bacterial cellulases are glycosylated as well, although the types and extents of decoration differ from their Eukaryotic counterparts. Our major findings are that glycosylation of CelA is uniform across its three linker peptides and composed of mainly galactose disaccharides (which is unique) and that this glycosylation dramatically impacts the hydrolysis of insoluble substrates, proteolytic and thermal stability, and substrate binding and changes the dynamics of the enzyme. This study suggests that the glycosylation of CelA is crucial for its exceptionally high cellulolytic activity on biomass and provides the robustness needed for this enzyme to function in harsh environments including industrial settings

High-throughput chemogenetic drug screening reveals PKC-RhoA/PKN as a targetable signaling vulnerability in GNAQ-driven uveal melanoma

Uveal melanoma (UM) is the most prevalent cancer of the eye in adults, driven by activating mutation of GNAQ/GNA11; however, there are limited therapies against UM and metastatic UM (mUM). Here, we perform a high-throughput chemogenetic drug screen in GNAQ-mutant UM contrasted with BRAF-mutant cutaneous melanoma, defining the druggable landscape of these distinct melanoma subtypes. Across all compounds, darovasertib demonstrates the highest preferential activity against UM. Our investigation reveals that darovasertib potently inhibits PKC as well as PKN/PRK, an AGC kinase family that is part of the "dark kinome." We find that downstream of the Gαq-RhoA signaling axis, PKN converges with ROCK to control FAK, a mediator of non-canonical Gαq-driven signaling. Strikingly, darovasertib synergizes with FAK inhibitors to halt UM growth and promote cytotoxic cell death in vitro and in preclinical metastatic mouse models, thus exposing a signaling vulnerability that can be exploited as a multimodal precision therapy against mUM.</p

Glycosylation Is Vital for Industrial Performance of Hyperactive Cellulases

In the terrestrial biosphere, biomass deconstruction is conducted by microbes employing a variety of complementary strategies, many of which remain to be discovered. Moreover, the biofuels industry seeks more efficient (and less costly) cellulase formulations upon which to launch the nascent sustainable bioenergy economy. The glycan decoration of fungal cellulases has been shown to protect these enzymes from protease action and to enhance binding to cellulose. We show here that thermal tolerant bacterial cellulases are glycosylated as well, although the types and extents of decoration differ from their Eukaryotic counterparts. Our major findings are that glycosylation of CelA is uniform across its three linker peptides and composed of mainly galactose disaccharides (which is unique) and that this glycosylation dramatically impacts the hydrolysis of insoluble substrates, proteolytic and thermal stability, and substrate binding and changes the dynamics of the enzyme. This study suggests that the glycosylation of CelA is crucial for its exceptionally high cellulolytic activity on biomass and provides the robustness needed for this enzyme to function in harsh environments including industrial settings

Perspective: The future of quantum dot photonic integrated circuits

Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries

Carrier recombination properties of low-threshold 1.3 μm quantum dot lasers on silicon

On-chip lasers are a key component for the realization of silicon photonics. The performance of silicon-based quantum dot (QD) devices is approaching equivalent QDs on native substrates. To drive forward design optimization we investigated the temperature and pressure dependence of intrinsic and modulation p-doped 1.3 μm InAs dot-in-well (DWELL) laser diodes on on-axis silicon substrates for comparison with devices on GaAs substrates. The silicon-based devices demonstrated low room temperature (RT) threshold current densities ( Jth ) of 192 Acm −2 (538 Acm −2 ) intrinsic (p-doped). Intrinsic devices exhibited temperature stable operation from 170–200 K. Above this, Jth increased more rapidly due to increased non-radiative recombination. P-doping increased the temperature at which Jth(T) started to increase to 300 K with a temperature insensitive region close to RT, but with a higher Jth . A strong correlation was found between the temperature dependence of gain spectrum broadening and the radiative component of threshold Jrad(T) . At low temperature this is consistent with strong inhomogeneous broadening of the carrier distribution, which is more pronounced in the p-doped devices. At higher temperatures Jth increases due to homogeneous thermal broadening coupled with non-radiative recombination. Hydrostatic pressure investigations indicate that while defect-related recombination dominates, radiative and Auger recombination also contribute to Jth