Two experiments divided by 33 years of booming semiconductor physics

Il Nuovo Cimento D - Two experiments are described, both of them virtually unpublished. One dates back to 1959, when Fumi was my teacher in Pavia, and concerns surface carrier mobility in...     

Realization of single and double axial InSb–GaSb heterostructure nanowires

Heteroepitaxial growth of III‐Sb nanowires allows for the formation of various interesting complex structures and enables the combination of their remarkable properties. In this Letter, we investigate the heteroepitaxial growth of Au‐seeded InSb and GaSb nanowires using metalorganic vapor phase epitaxy. We demonstrate successful single and double axial InSb–GaSb heterostructures in both directions. The formation properties of the grown nanowires including the compositional change of the particle and the interface sharpness are further discussed. In addition, the decomposition of InSb and GaSb segments and their side facet evolution are explained.

     

Growth and properties of InGaAs nanowires on silicon

Free‐standing ternary InGaAs nanowires (NW) are at the core of intense investigations due to their integration capabilities on silicon (Si) for next‐generation photovoltaics, integrated photonics, tunneling devices, and high‐performance gate all‐round III–V/Si NW transistors. In this review, recent progress on the growth, structural, optical and electrical properties of InGaAs NWs on Si substrate is highlighted. Particular focus is on a comparison between conventional catalyst‐assisted and catalyst‐free growth methods as well as self‐assembled versus site‐selectively grown NW arrays. It will be shown that catalyst‐free, high‐periodicity NW arrays with extremely high compositional uniformity are mandatory to allow un‐ambiguous structure–property correlation measurements. Here, interesting insights into the electronic/optical properties of wurtzite, zincblende and mixed crystal phases of InGaAs will be highlighted based on recent photoluminescence spectroscopy data. Finally, the InGaAs NW‐on‐Si system is also discussed in the realms of heterojunction properties, providing a promising system for steep‐slope tunneling field effect transistors in future low‐power post‐CMOS intergrated microelectronics and broad‐band photoabsorption and detec‐tion devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical study on lateral mode behavior of 660-nm InGaP/AlGaInP multiple-quantum-well laser diodes

Theoretical analysis for InGaP/AlGaInP laser diodes with different ridge waveguide structures is performed to investigate the lateral mode behavior using advanced device simulation. The internal physical mechanisms including temperature-induced changes in the refractive index profile, spatial hole burning effect, lateral carrier distribution, and gain profile variation with increasing input current are discussed by theoretical calculation to analyze the effects of different ridge structures on the lateral mode behavior of 660-nm AlGaInP laser diodes. The simulation results show that the use of narrow and shallow ridge geometry is the approach to obtaining single mode operation. Furthermore, it is found that the different values of the ridge height cause the lateral carrier distribution within the active region to be varied, which is also an important factor in determining the emergence of the first order lateral mode in addition to the geometry-dependent waveguide cutoff condition.     

衬底对化学气相沉积法制备氧化硅纳米线的影响

通过化学气相沉积法在不同衬底上制备了大量的氧化硅纳米线.选用衬底为Si片、带有约100nm厚SiO2氧化层Si片和石英片.利用场发射扫描电子显微镜(SEM)和透射电镜(TEM，配备有能谱仪)对样品的表面形貌、结构和成分进行研究.结果表明：这些纳米线都为非晶态，但在不同衬底上生长的纳米线形貌、尺寸和化学成分不同.讨论了各种衬底对不同特征氧化硅纳米线生长的影响. 关键词： 化学气相沉积 纳米线 纳米颗粒     

Influence of several factors on the growth of selenium nanowires induced by silver nanoparticles

This paper presents a study on the crystallization and growth mechanism of selenium nanowires induced by silver nanoparticles at ambient conditions with special reference to the effects of factors such as the shapes and size of silver nanoparticles, the induced reaction time, and the molar ratio of Ag⁰ to SeO₃²⁻ ions. The synthesis approach is conducted with no need of any stabilizers, and with no sonochemical process and/or templates. It is found that whether silver spherical particles or colloids can lead to the formation of nanowires with average diameter of 25 nm and lengths up to a few micrometers, and silver nanoplates lead to the formation of flat Se nanostructures. In particular, Au, Cu, Pt, and Pd particles cannot induce the growth of selenium nanowires in aqueous solution at room temperature. The results indicate that silver particles play a critical role in determining the growth of selenium nanowires. The lattice match between hexagonal-Se and orthorhombic- or trigonal-Ag₂Se particles is the major driving force in the growth of such nanostructures. The findings would be useful for design and construction of heterogeneous nanostructures with similar lattice parameter(s).     

Preparation of silver nanoparticles on zinc oxide nanowires by photocatalytic reduction for use in surface‐enhanced Raman scattering measurements

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurements, the high surface area of zinc oxide nanowires (ZnO NWs) was used. ZnO NWs on silicon substrates were prepared and used as substrates for further growth of silver nanoparticles (AgNPs). Ultraviolet (UV) irradiation was used to reduce silver ions to AgNPs on the ZnO wires. With proper growth conditions for both ZnO NWs and AgNPs, the substrates exhibit SERS enhancement factors greater than 10⁶. To understand the influences of the morphologies of the ZnO NWs on the growth of AgNPs, the growing time and temperature were varied. The concentration of silver nitrate and irradiation time of UV radiation were also varied. The resulting AgNPs were probed with para‐nitrothiophenol to quantify the SERS enhancements obtained from the varying conditions. The results indicate that ZnO NWs could be grown at temperatures higher than 490 °C and higher growth temperatures result in smaller diameter of the formed ZnO NWs. Also, the morphologies of ZnO NWs did not significantly alter the SERS signals. The concentration of silver nitrate affects the SERS signals significantly and the optimal concentration was found to be in the range of 10–20 mM. With irradiation times longer than 90 s, the resulting AgNPs showed similar SERS intensities. With optimized conditions, the AgNPs/ZnO substrates are highly suitable for SERS measurements with a typical enhancement factor of higher than 10⁶. Copyright © 2010 John Wiley & Sons, Ltd.     

Photochemical decoration of silver nanoparticles on ZnO nanowires as a three‐dimensional substrate for surface‐enhanced Raman scattering measurement

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurement, a three‐dimensional (3D) SERS substrate was prepared by the decoration of silver nanoparticles (AgNPs) on the side walls of ZnO nanowires. The prepared 3D SERS substrates provide the advantages of highly loaded density of AgNPs, with a large specific surface area to interact with analytes, and the ease for the analytes to access the surfaces of AgNPs. To prepare the substrates, ZnO nanowires were first grown on a glass plate by wet chemical method. By treating SnCl₂ on the surfaces of ZnO nanowires, Ag seeds could be formed on the side wall of the ZnO nanowires, which were further grown to a suitable size for SERS measurements via photochemical reduction. To optimize and understand the influences of the parameters used in preparation of the substrates, the reaction conditions were systematically adjusted and examined. Results indicated that AgNPs could be successfully decorated on the side wall of the ZnO nanowires only by the assistances of SnCl₂. The size and density of AgNPs were affected by both the concentration of silver nitrate and the irradiation time. With optimized condition, the prepared 3D substrates provided an enhancement factor approaching 7 orders of magnitude compared with conventional Raman intensity. Copyright © 2014 John Wiley & Sons, Ltd.     

Composition dependence on dispersion of Au/Cu bimetallic nanoparticles in nylon 11 thin films

Effect of composition on the dispersion of Au_xCu_1-x bimetallic nanoparticles into nylon 11 matrix has been investigated. TEM, EDX, and XPS depth profiling were used for characterizing the changes in the composition of the bimetallic particles and in the depth distribution of the particles in the nylon 11 layer caused by heat treatment in N₂ atmosphere. The island-like bimetallic particles were found to be formed on the nylon 11 surface before heat treatment. The results of XPS depth profiling revealed that, by the heat treatment, the Au_xCu_1-x bimetallic particles with x? 0.55 were not dispersed into the nylon 11 layer while those with x≥ 0.70 were homogeneously dispersed in the films, indicating the existence of critical composition for penetration of the bimetallic particles. By comparing the composition and structure of the bimetallic particles, the cause of these finding is discussed in terms of surface free energy of the particles. Received 29 November 2000     

Effect of temperature and silicon resistivity on the elaboration of silicon nanowires by electroless etching

The morphology of silicon nanowire (SiNW) layers formed by Ag-assisted electroless etching in HF/H₂O₂ solution was studied. Prior to the etching, the Ag nanoparticles were deposited on p-type Si(1 0 0) wafers by electroless metal deposition (EMD) in HF/AgNO₃ solution at room temperature. The effect of etching temperature and silicon resistivity on the formation process of nanowires was studied. The secondary ion mass spectra (SIMS) technique is used to study the penetration of silver in the etched layers. The morphology of etched layers was investigated by scanning electron microscope (SEM).     

Performance improvement for epitaxially grown SiGe on Si solar cell by optimizing the back surface field

This letter reports on the performance improvement of an epitaxially grown SiGe on Si solar cell by optimizing the back surface field (BSF). First, a Si_0.18Ge_0.82 on silicon (Si) solar cell was fabricated with a 0.25 μm BSF layer. A 25 mV open‐circuit voltage (V_OC) improvement was observed on this BSF solar cell compared with the reference solar cell without BSF layer. Then, a Si_0.18Ge_0.82 on Si solar cell with double BSF layers was designed and fabricated. The measured efficiency of this solar cell is 3.4% when filtered by a GaAs_0.79P_0.21 top cell. To the best of the authors' knowledge, the 3.4% efficiency reported here is the highest efficiency for SiGe on Si solar cells when filtered by a GaAs_0.79P_0.21 top cell. The previous best reported efficiency for high Ge composition SiGe on Si solar cell was only 1.7% when filtered by a GaAs_0.79P_0.21 top cell.     

Synthesis and microstructure of metal oxide thin films containing metal nanoparticles by liquid phase deposition (LPD) method

Au nanoparticles dispersed SiO₂-TiO₂ composite films have been prepared by a novel wet process, Liquid Phase Deposition (LPD) method. The composite films were characterized by XRD, XPS, TEM, ICP, SEM and UV-VIS absorption spectroscopy. The results showed that the SiO₂-TiO₂ composite films containing Au^III and Au^I ionic species were co-deposited from a mixed solution of ammonium silicofluoride, ammonium hexafluorotitanate, boric acid and tetrachloroauric acid. The heat treatment induced the reduction of Au ions and formation of Au nanoparticles in the film. TEM observation revealed that the Au nanoparticles with 5-10 nm in diameter were found to be dispersed uniformly in the SiO₂-TiO₂ matrix. The optical absorption band due to the surface plasmon resonance of dispersed Au particles were observed at the wavelength of 550 nm and shifted toward longer wavelength with increasing heat treatment temperature. Received 28 November 2000     

Investigation of electron delay in the base on noise performance in InGaP heterojunction bipolar transistors

The DC, RF and noise characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with different base layer widths and δ‐doped layer in the collector were investigated. Analysis of the RF and noise characteristics revealed that the high frequency noise of these HBTs is reduced due to cross‐correlation of shot noise sources and Coulomb blockade from accumulated charge. The measured noise performance is in a good agreement with the HICUM L2 compact model [M. Schroter, IEICE Trans. Electron. E88‐C , 1098 (2005)] when correlated shot noise sources with Fano factor for collector shot noise are included.

     

Comparison of the band alignment of strained and strain-compensated GaInNAs QWs on GaAs and InP substrates

We present a comparison of the band alignment of the Ga_1−xIn_xN_yAs_1−y active layers on GaAs and InP substrates in the case of conventionally strained and strain-compensated quantum wells. Our calculated results present that the band alignment of the tensile-strained Ga_1−xIn_xN_yAs_1−y quantum wells on InP substrates is better than than that of the compressively strained Ga_1−xIn_xN_yAs_1−y quantum wells on GaAs substrates and both substrates provide deeper conduction wells. Therefore, tensile-strained Ga_1−xIn_xN_yAs_1−y quantum wells with In concentrations of x0.53 on InP substrates can be used safely from the band alignment point of view when TM polarisation is required. Our calculated results also confirm that strain compensation can be used to balance the strain in the well material and it improves especially the band alignment of dilute nitride Ga_1−xIn_xN_yAs_1−y active layers on GaAs substrates. Our calculations enlighten the intrinsic superiority of N-based lasers and offer the conventionally strained and strain-compensated Ga_1−xIn_xN_yAs_1−y laser system on GaAs and InP substrates as ideal candidates for high temperature operation.     

Effect of the shell on the transport properties of poly(glycerol) and Poly(ethylene imine) nanoparticles

Dendritic core–shell architectures containing poly (glycerol) and poly (ethylene imine) cores and poly(lactide) shell (PG-PLA and PEI-PLA respectively) were synthesized. Analogous of these core–shell architectures containing the same cores but poly (L-lactide) shell (PG-PLLA and PEI-PLLA, respectively) were also synthesized. In this work PG and PEI were used as macroinitiator for ring opening polymerization of the lactid and L-lactide monomers. Different molar ratios of monomer to end functional groups of PG ([LA]/[OH]) and PEI ([LA]/[NHn] (n = 1 or 2)) were used to prepare the core–shell architectures with different shell thickness. These core–shell architectures were able to encapsulate and transport the small guest molecules. Their transport capacity (TC) depended on the type and thickness of the shells. TC of core–shell architectures containing PLLA shell was higher than that for their analogs containing PLA shell. The diameter of core–shell architectures was between 20–80 nm. The rate of release of guest molecules from chloroform solution of nanocarriers to water phase was investigated and it depended on the type of the core, shell and solvent.     

Effect of chitosan and thiolated chitosan coating on the inhibition behaviour of PIBCA nanoparticles against intestinal metallopeptidases

Surface modified nanoparticles composed of poly(isobutylcyanoacrylate) (PIBCA) cores surrounded by a chitosan and thiolated chitosan gel layer were prepared and characterized in previous works. The presence of such biopolymers on the nanoparticle surface conferred those nanosystems interesting characteristics that might partially overcome the gastrointestinal enzymatic barrier, improving the oral administration of pharmacologically active peptides. In the present work, the antiprotease behaviour of this family of core–shell nanoparticles was in vitro tested against two model metallopeptidases present in the gastrointestinal tract (GIT): Carboxypeptidase A -CP A- (luminal protease) and Leucine Aminopeptidase M -LAP M- (membrane protease). As previous step, the zinc-binding capacity of these nanoparticles was evaluated. Interestingly, an improvement of both the zinc-binding capacity and the antiprotease effect of chitosan was observed when the biopolymers (chitosan and thiolated chitosan) were used as coating component of the core–shell nanoparticles, in comparison with their behaviour in solution, thanks to the different biopolymer chains rearrangement. The presence of amino, hydroxyl and thiol groups on the nanoparticle surface promoted zinc binding and hence the inhibition of the metallopeptidases analysed. On the contrary, the occurrence of a cross-linked structure in the gel layer surrounding the PIBCA cores of thiolated formulations, due to the formation of interchain and intrachain disulphide bonds, partially limited the inhibition of the proteases. The low accessibility of cations to the active groups of the cross-linked polymeric shell was postulated as a possible explanation of this behaviour. Results obtained in this work make this family of surface-modified nanocarriers promising candidates for the successfull administration of pharmacologically active peptides and proteins by the oral route.     

The effect of oxidation on the structure of nickel nanoparticles

The structural properties of nickel nanoparticles which are prepared by means of DC sputtering in argon and subsequently oxidized in ambient air are reported. Ex situ structural and chemical investigations utilizing (high resolution) transmission electron microscopy and electron energy loss spectroscopy reveal that the particles consist of a metallic core surrounded by an oxide shell. The lattice constant of the nickel core is found to increase significantly with decreasing particle size. This widening of the nickel lattice is attributed to an interfacial stress that originates from the lattice mismatch between nickel and nickel oxide. Received 21 December 2000     

An analysis of the effect of nitrogen and a screened (by free carriers) Coulomb field on the binding energy of hydrogenic shallow donors in GaInAsN

The effect of nitrogen concentration on the screening with free carriers and binding energy of hydrogenic shallow donors in GaInAsN alloys is investigated. The binding energy is calculated using a novel algebraic model which was proposed recently by Gönül et al. (2006) [16], in order to find an analytical solution to the screened Coulomb potential. The results show that the nitrogen concentration is a strong factor in producing a screening field of free carriers and in affecting the binding energy of hydrogenic shallow donors.     

Ab initio study of the diffusion mechanisms of gallium in a silicon matrix

We present the results of a study into the diffusion mechanisms of Ga defects in crystalline Si using ab initio techniques. Five stable neutral configurations for single and multi-atom defects are identified by density-functional theory (DFT) calculations within the local density approximation and using a localized basis set as implemented in the SIESTA package. Formation energy (E _F ) calculations on these stable structures show the most likely neutral single-atom defect to be the Ga substitutional, with an E _F of 0.7 eV in good agreement with previous work. Charge state studies show the Ga tetrahedral interstitial defect to be in a + 1 state for most doping conditions. They also indicate the possibility for a gallium substitutional-tetrahedral interstitial complex to act as a deactivating center for the Ga dopants except in n-doped regime, where the complex adopts a − 1 charge state. Migration pathway calculations using SIESTA coupled with the activation relaxation technique (ART nouveau) allow us to determine possible migration paths from the stable configurations found, under various charge states. In general, diffusion barriers decrease as the charge state becomes more negative, suggesting that the presence of Si self-interstitials can enhance diffusion through the kicking out of substitutional Si and by adding negative charge carriers to the system. An overall picture of a possible Ga diffusion and complex formation mechanism is presented based on these results.     

The effects of carrier degeneracy on transport properties of the double heterostructure injection laser

It is shown that carrier degeneracy plays an important role in determining the electrical properties of double heterostructure injection lasers. Correct statistical treatment of the charge cariers in the device leads to a generalised Einstein relation between the carrier transport coefficients. Such a relation (for both electrons and holes) is used in numerical solutions of semiconductor transport equations applicable to the laser. Experimentally observed I–V characteristics of the laser are explained in terms of carrier degeneracy effects.