Gain characteristics of 1.55-μm high-speed multiple-quantum-welllasers

We describe the important characteristics of high-speed p-doped compressively strained MQW lasers obtained from comprehensive below-threshold DC measurements. Results of gain and differential gain versus wavelength and carrier density are verified by above-threshold resonance measurements. Measurement-derived design curves of gain, differential gain, and linewidth enhancement factor allow device optimization for high speed and low chirp     

Spherical Particles of Zirconia-Titania of Hexagonal Structure from a Neutral Amine Route

Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Effect of p-doping on the temperature dependence of differentialgain in FP and DFB 1.3-μm InGaAsP-InP multiple-quantum-well lasers

The temperature dependence of differential gain dG/dn for 1.3-μm InGaAsP-InP FP and DFB lasers with two profiles of p-doping was obtained from RIN measurements within the temperature range of 25°C-65°C. Experiments showed that the change of the active region doping level from 3·10¹⁷ cm^-3 to 3·10¹⁸ cm^-3 leads to a 50% increase of the differential gain for FP lasers at 25°C. Heavily doped devices also exhibit more rapid reduction of the differential gain with increasing temperature. The effect of active region doping on the energy separation between the electron Fermi level and electronic states coupled into the laser mode explains the observations. The temperature dependence of differential gain for DFB devices strongly depends on the detuning of the lasing wavelength from the gain peak     

S-band low noise amplifier using 1μm InGaAs/InAlAs/InP pHEMT

正This paper discusses the design of a wideband low noise amplifier(LNA) in which specific architecture decisions were made in consideration of system-on-chip implementation for radio-astronomy applications.The LNA design is based on a novel ultra-low noise InGaAs/InAlAs/InP pHEMT.Linear and non-linear modelling of this pHEMT has been used to design an LNA operating from 2 to 4 GHz.A common-drain in cascade with a common source inductive degeneration,broadband LNA topology is proposed for wideband applications.The proposed configuration achieved a maximum gain of 27 dB and a noise figure of 0.3 dB with a good input and output return loss(S_(11)—10 dB,S_(22)—11 dB).This LNA exhibits an input 1-dB compression point of-18 dBm,a third order input intercept point of 0 dBm and consumes 85 mW of power from a 1.8 V supply.     

Highly conducting π-conjugated molecular junctions covalently bonded to gold electrodes

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au-C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ, resulting in formation of a direct covalent σ bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated π system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the π system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G(0) = 2e(2)/h). Junctions formed with methylene-terminated oligophenyls with two to four phenyl units show a 100-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling, as they exhibit an exponential dependence of conductance on oligomer length. In addition, density functional theory based calculations for the Au-xylylene-Au junction show near-resonant transmission, with a crossover to tunneling for the longer oligomers.     

Semiconductor‐Based Photoelectrochemical Water Splitting at the Limit of Very Wide Depletion Region

In semiconductor‐based photoelectrochemical (PEC) water splitting, carrier separation and delivery largely relies on the depletion region formed at the semiconductor/water interface. As a Schottky junction device, the trade‐off between photon collection and minority carrier delivery remains a persistent obstacle for maximizing the performance of a water splitting photoelectrode. Here, it is demonstrated that the PEC water splitting efficiency for an n‐SrTiO₃ (n‐STO) photoanode is improved very significantly despite its weak indirect band gap optical absorption (α < 10⁴ cm^?1), by widening the depletion region through engineering its doping density and profile. Graded doped n‐SrTiO₃ photoanodes are fabricated with their bulk heavily doped with oxygen vacancies but their surface lightly doped over a tunable depth of a few hundred nanometers, through a simple low temperature reoxidation technique. The graded doping profile widens the depletion region to over 500 nm, thus leading to very efficient charge carrier separation and high quantum efficiency (>70%) for the weak indirect transition. This simultaneous optimization of the light absorption, minority carrier (hole) delivery, and majority carrier (electron) transport by means of a graded doping architecture may be useful for other indirect band gap photocatalysts that suffer from a similar problem of weak optical absorption.