A 0.2-W Heterostructure Barrier Varactor Frequency Tripler at 113 GHz

We present a high-power InAlAs/InGaAs/InP heterostructure barrier varactor (HBV) frequency tripler. The HBV device topology was designed for efficient thermal dissipation and high efficiency. To verify simulations, the device was flip-chip soldered onto embedding microstrip circuitry on an aluminum nitride substrate. This hybrid circuit was then mounted in a waveguide block without any movable tuners. From the resulting RF measurements, the maximum output power was 195 mW at 113 GHz, with a conversion efficiency of 15%. The measured 3-dB bandwidth was 1.5%     

Performance characteristics of buried heterostructure VCSELs usingsemi-insulating GaInP:Fe regrowth

We have fabricated GaAs-AlGaAs buried heterostructure vertical cavity surface emitting lasers, emitting at 850 mm, using semi-insulating GaInP:Fe regrowth and investigated their static properties. Lasers of different size (10-21 μm) have threshold currents in the range 2.8-7.0 mA, and produce a maximum output power of 1.7-6.0 mW at room temperature. The variation of threshold current with device size shows that the leakage current at the regrowth interface accounts for a significant part of the injection current. In spite of this, a differential quantum efficiency in the range 20%-30% is obtained which indicates that the regrowth interface is smooth and does not introduce any significant scattering loss. Studies of the transverse mode properties suggest that the GaInP provides weak guiding, resulting in single mode operation up to an output power of 0.7 mW and a beam divergence of only 60 for lasers as large as 10 μm     

Single fundamental-mode output power exceeding 6 mW from VCSELs with a shallow surface relief

A single fundamental-mode output power of 6.5 mW was achieved from an 850-nm vertical-cavity surface-emitting laser (VCSEL) with a shallow surface relief, the highest single-mode power ever reported using this technique. The VCSELs were fabricated from epitaxial material grown to yield an antiphase reflection from the topmost layer. A circular surface relief, acting as a mode discriminator, was etched in the center to reduce the mirror loss for the fundamental mode. This "inverted" surface-relief technique offers relaxed etch depth control and, therefore, improves reproducibility and yield.     

Correction to: On a variant of Pillai’s problem with transcendental numbers

Acta Mathematica Hungarica -     

Monolithic integration of continuous-relief diffractive structures with vertical-cavity surface-emitting lasers

In this work, we have studied the transfer of diffractive optical elements (DOEs), originally made in resist, into GaAs for monolithic integration with vertical-cavity surface-emitting lasers (VCSELs). The DOEs are blazed gratings and Fresnel lenses, and have been fabricated on the back surface of bottom emitting VCSELs using electron-beam lithography or replication by hot embossing in resist followed by a quick-dry etch step. Diffraction efficiency was measured to be 81% in the first order of diffraction for the blazed grating.     

Thermal constraints for heterostructure barrier varactors

Current research on heterostructure barrier varactors (HBVs) devotes much effort to the generation of very high power levels in the millimeter wave region. One way of increasing the power handling capacity of HBVs is to stack several barriers epitaxially. However, the small device dimensions lead to very high temperatures in the active layers, deteriorating the performance. We have derived analytical expressions and combined those with finite element simulations, and used the results to predict the maximum effective number of barriers for HBVs. The thermal model is also used to compare the peak temperature and power handling capacity of GaAs and InP-based HBVs. It is argued that InP-based devices may be inappropriate for high-power applications due to the poor thermal conductivity of the InGaAs modulation layers.     

Optimization of the UTC-PD Epitaxy for Photomixing at 340 GHz

We present a method to optimize the epitaxial layer structure of an InGaAs/InP uni-traveling-carrier photo-diode (UTC-PD) for continuous THz-wave generation. The design approach used is general in that it can be applied for any target frequency while this study focuses on 340 GHz. The photodiode epitaxy is modeled and optimized using a TCAD software implementing the hydrodynamic semiconductor equations. This physical device model was found to be in good agreement with reported experimental results. It is shown that the UTC-PD can generate ~1 mW at 340 GHz by choosing the optimum absorption layer and collection layer thicknesses.     

Optimization of the UTC-PD Epitaxy for Photomixing at 340?GHz

We present a method to optimize the epitaxial layer structure of an InGaAs/InP uni-traveling-carrier photo-diode (UTC-PD) for continuous THz-wave generation. The design approach used is general in that it can be applied for any target frequency while this study focuses on 340 GHz. The photodiode epitaxy is modeled and optimized using a TCAD software implementing the hydrodynamic semiconductor equations. This physical device model was found to be in good agreement with reported experimental results. It is shown that the UTC-PD can generate ~1 mW at 340 GHz by choosing the optimum absorption layer and collection layer thicknesses.     

Study of antimicrobial properties of cotton medical textiles treated with citric acid and dried/cured by microwaves

The purpose of this study was to examine antibacterial and antifungal activity of antibacterial finish based on Citric acid on cotton medical textiles. The ability to effectively reduce the number of gram-negative, gram-positive bacteria and yeast was evaluated, specifically comparing the antibacterial activity after two different drying/curing methods. Citric acid (CA) and diethyl–tetradecyl–[3–(trimethoxysilyl)-propyl] ammonium chloride (Quat) were used for hygiene and disinfection purposes of medical textiles in this study. It was applied by pad-dry process and its fixation to cellulose hydroxyls was enhanced either by high curing temperatures or microwaves (MW). Determination of antibacterial activity of finished products was performed according to ISO 20743:2007 standard before the washing and after the 10 washing cycles. Antibacterial activity was tested against gram-negative bacteria, Escherichia coli, gram-positive-Staphylococcus aureus and yeast, Candida albicans. Obtained results are confirming the possibility of eco-friendly CA application, for the purpose of antimicrobial finishing of cotton medical textiles. Prevention of nosocomial infections with the Citric acid is possible using both curing methods (convection and microwave) and furthermore, the treatment is durable up to 10 washing cycles. Citric acid, as one of the suitable active substances is crosslinked to the cellulose hydroxyls by the formation of ester linkages. Its antimicrobial effectiveness against the chosen microorganisms proved to be the best against S. aureus. Applied finish bath has additional crease proof effectiveness providing sufficient both antimicrobial and crease proof effectiveness, so as the durability against 10 washing cycles.