Control of unpolarized emission in closely stacked InAs quantum dot structure

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.     

Antibacterial and antifungal properties of crude extracts and isolated compounds from Lychnophora markgravii

Abstract

Antimicrobial activity of dichloromethane and ethanol extracts and five compounds: pinostrobin (I), pinocembrin (II), tectochrysin (III), galangin 3-methyl ether (IV) and tiliroside (V) isolated from Lychnophora markgravii aerial parts against fifteen microorganisms was determined. The structures of these compounds were elucidated based on ESI-MS and NMR spectroscopic data. Both extracts showed antimicrobial activity against several tested microorganisms. Pinostrobin, tectochrysin and galangin 3-methyl ether showed the strongest antibacterial and antifungal effects.     

DLTS characterization of silicon nitride passivated AlGaN/GaN heterostructures

Passivating the ungated surface of AlGaN/GaN HEMTs with silicon nitride (SiN) is effective in improving the microwave output power performances of these devices. However, very little information is available about surface states in GaN-based HEMTs after SiN passivation. In this work we investigate AlGaN/GaN HEMTs structures having either metal–semiconductor or metal–SiN–semiconductor gate contacts. In short gate devices conductance DLTS measurements point out a hole-like peak that shows an anomalous behaviour and can be ascribed to surface states in the access regions of the device. In insulated gate HEMTs a band of levels is detected and ascribed to surface states, whose energy ranges from 0.14 to 0.43 eV. Capacitance–voltage measurements allow us to point out the existence of a second band of interface states deeper in energy than the former one. This band is responsible for slow transients observed in the characteristics of the insulated gate FAT-HEMT.     

Tuning of long-wavelength emission in InxGa1−xAs quantum dot structures

This work explores the conditions to obtain the extension of the PL emission beyond 1.3 μm in InGaAs quantum dot (QD) structures growth by MOCVD. We found that, by controlling the In incorporation in the barrier embedding the QDs, the wavelength emission can be continuously tuned from 1.25 μm up to 1.4 μm at room temperature. However, the increase in the overall strain of the structures limits the possibility to increase the maximum gain in the QD active device, where an optical density as high as possible is required. By exploring the kinetics of QD surface reconstruction during the GaAs overgrowth, we are able to obtain, for the first time, emission beyond 1.3 μm from InGaAs QDs grown on GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm and significant improvements in terms of line shape narrowing and room temperature efficiency are obtained. The temperature-dependent quenching of the emission efficiency is reduced down to a factor of 3, the best value ever reported for QD structures emitting at 1.3 μm.