silicon and gallium-arsenide

Progress in personal computing has recently permitted small research programs to design and simulate application-specific integrated circuits (ASICs). Inexpensive fabrication of silicon chips can then be obtained using chip foundries, and quite complex circuits can be greatly reduced in size with an accompanying increase in certain performance characteristics. Within the past 5 years it has also become possible to design ASICs which can transmit and receive radio signals and which thus may be employed in applications in which wired connections for input and output of signals are not practicable. We are currently developing research-grade prototype ASICs for the monitoring of human vital signs. In this case one or more sensors placed on an ASIC provides a signal to be transmitted a distance of 2-3 meters to a receiver/display unit. The use of ASIC telesensors provides the possibility of wireless monitoring, including long-term monitoring, with inexpensive and unencumbering devices. Their self-contained nature permits a number of potential uses in future biomedical applications as new sensors are devised which are amenable to deployment on silicon.

Topics: Arsenicals; Body Temperature; Electronics, Medical; Equipment Design; Forecasting; Gallium; Humans; Miniaturization; Monitoring, Physiologic; Silicon; Transistors, Electronic

Polarization-dependent scattering anisotropy of cylindrical nanowires has numerous potential applications in, for example, nanoantennas, photothermal therapy, thermophotovoltaics, catalysis, sensing, optical filters and switches. In all these applications, temperature-dependent material properties play an important role and often adversely impact performance depending on the dominance of either radiative or dissipative damping. Here, we employ numerical modeling based on Mie scattering theory to investigate and compare the temperature and polarization-dependent optical anisotropy of metallic (gold, Au) nanowires with indirect (silicon, Si) and direct (gallium arsenide, GaAs) bandgap semiconducting nanowires. Results indicate that plasmonic scattering resonances in semiconductors, within the absorption band, deteriorate with an increase in temperature whereas those occurring away from the absorption band strengthen as a result of the increase in phononic contribution. Indirect-bandgap thin ([Formula: see text]) Si nanowires present low absorption efficiencies for both the transverse electric (TE, [Formula: see text]) and magnetic (TM, [Formula: see text]) modes, and high scattering efficiencies for the TM mode at shorter wavelengths making them suitable as highly efficient scatterers. Temperature-resilient higher-order anapole modes with their characteristic high absorption and low scattering efficiencies are also observed in the semiconductor nanowires ([Formula: see text] nm) for the TE polarization. Herein, the GaAs nanowires present [Formula: see text] times greater absorption efficiencies compared to the Si nanowires making them especially suitable for temperature-resilient applications such as scanning near-field optical microscopy (SNOM), localized heating, non-invasive sensing or detection that require strong localization of energy in the near field.

Topics: Gallium; Nanowires; Semiconductors; Silicon

In (para-)thyroid surgery iatrogenic parathyroid injury should be prevented. To aid the surgeons' eye, a camera system enabling parathyroid-specific image enhancement would be useful. Hyperspectral camera technology might work, provided that the spectral signature of parathyroid tissue offers enough specific features to be reliably and automatically distinguished from surrounding tissues. As a first step to investigate this, we examined the feasibility of wide band diffuse reflectance spectroscopy (DRS) for automated spectroscopic tissue classification, using silicon (Si) and indium-gallium-arsenide (InGaAs) sensors.. DRS (350-1830 nm) was performed during (para-)thyroid resections. From the acquired spectra 36 features at predefined wavelengths were extracted. The best features for classification of parathyroid from adipose or thyroid were assessed by binary logistic regression for Si- and InGaAs-sensor ranges. Classification performance was evaluated by leave-one-out cross-validation.. In 19 patients 299 spectra were recorded (62 tissue sites: thyroid = 23, parathyroid = 21, adipose = 18). Classification accuracy of parathyroid-adipose was, respectively, 79% (Si), 82% (InGaAs) and 97% (Si/InGaAs combined). Parathyroid-thyroid classification accuracies were 80% (Si), 75% (InGaAs), 82% (Si/InGaAs combined).. Si and InGaAs sensors are fairly accurate for automated spectroscopic classification of parathyroid, adipose and thyroid tissues. Combination of both sensor technologies improves accuracy. Follow-up research, aimed towards hyperspectral imaging seems justified. Copyright © 2016 John Wiley & Sons, Ltd.

Topics: Adipose Tissue; Adolescent; Adult; Aged; Arsenicals; Automation; Calibration; Electronic Data Processing; Equipment Design; Female; Gallium; Humans; Indium; Male; Middle Aged; Parathyroid Glands; Regression Analysis; Silicon; Spectrophotometry; Spectrum Analysis; Thyroid Gland; Young Adult

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G 0 = 4e (2)/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G 0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm(-1), fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G 0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm(-1), which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm(-1) and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies.

Topics: Arsenicals; Carbon; Gallium; Nanotechnology; Nanotubes, Carbon; Particle Size; Semiconductors; Silicon; Surface Properties; Transistors, Electronic

By applying a texturing process to silicon substrates, we demonstrate the possibility to integrate III-V nanowires on (100) oriented silicon substrates. Nanowires are found to grow perpendicular to the {111}-oriented facets of pyramids formed by KOH etching. Having control of the substrate orientation relative to the incoming fluxes enables not only the growth of nanowires on selected facets of the pyramids but also studying the influence of the fluxes on the nanowire nucleation and growth. Making use of these findings, we show that nanowires with different dimensions can be grown on the same sample and, additionally, it is even possible to integrate nanowires of different semiconductor materials, for example, GaAs and InAs, on the very same sample.

Topics: Adsorption; Arsenicals; Crystallization; Gallium; Indium; Materials Testing; Nanocomposites; Nanowires; Particle Size; Silicon; Surface Properties; Systems Integration

In colorectal surgery, detecting ureters and mesenteric arteries is of utmost importance to prevent iatrogenic injury and to facilitate intraoperative decision making. A tool enabling ureter- and artery-specific image enhancement within (and possibly through) surrounding adipose tissue would facilitate this need, especially during laparoscopy. To evaluate the potential of hyperspectral imaging in colorectal surgery, we explored spectral tissue signatures using single-spot diffuse reflectance spectroscopy (DRS). As hyperspectral cameras with silicon (Si) and indium gallium arsenide (InGaAs) sensor chips are becoming available, we investigated spectral distinctive features for both sensor ranges.. In vivo wide-band (wavelength range 350-1830 nm) DRS was performed during open colorectal surgery. From the recorded spectra, 36 features were extracted at predefined wavelengths: 18 gradients and 18 amplitude differences. For classification of respectively ureter and artery in relation to surrounding adipose tissue, the best distinctive feature was selected using binary logistic regression for Si- and InGaAs-sensor spectral ranges separately. Classification performance was evaluated by leave-one-out cross-validation.. In 10 consecutive patients, 253 spectra were recorded on 53 tissue sites (including colon, adipose tissue, muscle, artery, vein, ureter). Classification of ureter versus adipose tissue revealed accuracy of 100% for both Si range and InGaAs range. Classification of artery versus surrounding adipose tissue revealed accuracies of 95% (Si) and 89% (InGaAs).. Intraoperative DRS showed that Si and InGaAs sensors are equally suited for automated classification of ureter versus surrounding adipose tissue. Si sensors seem better suited for classifying artery versus mesenteric adipose tissue. Progress toward hyperspectral imaging within this field is promising.

Topics: Adipose Tissue; Aged; Aged, 80 and over; Arsenicals; Colorectal Surgery; Female; Gallium; Humans; Indium; Male; Mesenteric Arteries; Middle Aged; Silicon; Spectrum Analysis; Surgery, Computer-Assisted; Ureter

Strong surface and impurity scattering in III-V semiconductor-based nanowires (NW) degrade the performance of electronic devices, requiring refined concepts for controlling charge carrier conductivity. Here, we demonstrate remote Si delta (δ)-doping of radial GaAs-AlGaAs core-shell NWs that unambiguously exhibit a strongly confined electron gas with enhanced low-temperature field-effect mobilities up to 5 × 10(3) cm(2) V(-1) s(-1). The spatial separation between the high-mobility free electron gas at the NW core-shell interface and the Si dopants in the shell is directly verified by atom probe tomographic (APT) analysis, band-profile calculations, and transport characterization in advanced field-effect transistor (FET) geometries, demonstrating powerful control over the free electron gas density and conductivity. Multigated NW-FETs allow us to spatially resolve channel width- and crystal phase-dependent variations in electron gas density and mobility along single NW-FETs. Notably, dc output and transfer characteristics of these n-type depletion mode NW-FETs reveal excellent drain current saturation and record low subthreshold slopes of 70 mV/dec at on/off ratios >10(4)-10(5) at room temperature.

Topics: Aluminum; Arsenicals; Electrons; Gallium; Nanotechnology; Nanowires; Semiconductors; Silicon

Today's consumer electronics, such as cell phones, tablets and other portable electronic devices, are typically made of non-renewable, non-biodegradable, and sometimes potentially toxic (for example, gallium arsenide) materials. These consumer electronics are frequently upgraded or discarded, leading to serious environmental contamination. Thus, electronic systems consisting of renewable and biodegradable materials and minimal amount of potentially toxic materials are desirable. Here we report high-performance flexible microwave and digital electronics that consume the smallest amount of potentially toxic materials on biobased, biodegradable and flexible cellulose nanofibril papers. Furthermore, we demonstrate gallium arsenide microwave devices, the consumer wireless workhorse, in a transferrable thin-film form. Successful fabrication of key electrical components on the flexible cellulose nanofibril paper with comparable performance to their rigid counterparts and clear demonstration of fungal biodegradation of the cellulose-nanofibril-based electronics suggest that it is feasible to fabricate high-performance flexible electronics using ecofriendly materials.

Topics: Arsenicals; Biodegradation, Environmental; Cellulose; Gallium; Microwaves; Nanofibers; Paper; Phanerochaete; Silicon; Smartphone

We investigate theoretically the optomechanical interactions inside cavities created in two-dimensional infinite phoXonic crystals constituted by a square array of holes in silicon (Si) and gallium arsenide (GaAs) matrices. The cavity is simply obtained by removing one hole in the perfect crystal. Our calculations take into account two mechanisms that contribute to the optomechanical coupling, namely the bulk photoelastic effect and the deformations of the interfaces due to the acoustic strain. The coupling strength is estimated by two different methods, modulation of the photonic mode frequency during one period of the acoustic oscillations and calculation of the optomechanical coupling rate. We discuss the important roles of the symmetry and degeneracy of the modes to discriminate which ones are not able to interact efficiently. Calculations in Si and GaAs crystals at different optical wavelengths emphasize the dependence of the photoelastic contribution to the optomechanical interaction as a function of material and wavelength, especially owing to the significant variation of the photoelastic coefficients near the semiconductor band gap.

Topics: Arsenicals; Crystallization; Gallium; Mechanical Phenomena; Models, Chemical; Optical Phenomena; Silicon

Thanks to their unique morphology, nanowires have enabled integration of materials in a way that was not possible before with thin film technology. In turn, this opens new avenues for applications in the areas of energy harvesting, electronics, and optoelectronics. This is particularly true for axial heterostructures, while core-shell systems are limited by the appearance of strain-induced dislocations. Even more challenging is the detection and understanding of these defects. We combine geometrical phase analysis with finite element strain simulations to quantify and determine the origin of the lattice distortion in core-shell nanowire structures. Such combination provides a powerful insight in the origin and characteristics of edge dislocations in such systems and quantifies their impact with the strain field map. We apply the method to heterostructures presenting single and mixed crystalline phase. Mixing crystalline phases along a nanowire turns out to be beneficial for reducing strain in mismatched core-shell structures.

Topics: Arsenicals; Crystallization; Elasticity; Finite Element Analysis; Gallium; Nanowires; Semiconductors; Silicon

We report a new type of single InAs quantum dot (QD) embedded at the junction of gold-free branched GaAs/AlGaAs nanowire (NW) grown on silicon substrate. The photoluminescence intensity of such QD is ~20 times stronger than that from randomly distributed QD grown on the facet of straight NW. Sharp excitonic emission is observed at 4.2 K with a line width of 101 μeV and a vanishing two-photon emission probability of g(2)(0) = 0.031(2). This new nanostructure may open new ways for designing novel quantum optoelectronic devices.

Topics: Arsenicals; Equipment Design; Gallium; Indium; Nanostructures; Nanotechnology; Nanowires; Quantum Dots; Silicon

By employing various high-resolution metrology techniques we directly probe the material composition profile within GaAs-Al0.3Ga0.7As core-shell nanowires grown by molecular beam epitaxy on silicon. Micro Raman measurements performed along the entire (>10 μm) length of the [111]-oriented nanowires reveal excellent average compositional homogeneity of the nominally Al0.3Ga0.7As shell. In strong contrast, along the radial direction cross-sectional scanning transmission electron microscopy and associated chemical analysis reveal rich structure in the AlGaAs alloy composition due to interface segregation, nanofaceting, and local alloy fluctuations. Most strikingly, we observe a 6-fold Al-rich substructure along the corners of the hexagonal AlGaAs shell where the Al-content is up to x ~ 0.6, a factor of 2 larger than the body of the AlGaAs shell. This is associated with facet-dependent capillarity diffusion due to the nonplanarity of shell growth. A modulation of the Al-content is also found along the radial [110] growth directions of the AlGaAs shell. Besides the ~10(3)-fold enhancement of the photoluminescence yield due to inhibition of nonradiative surface recombination, the AlGaAs shell gives rise to a broadened band of sharp-line luminescence features extending ~150-30 meV below the band gap of Al0.3Ga0.7As. These features are attributed to deep level defects under influence of the observed local alloy fluctuations in the shell.

Topics: Alloys; Arsenicals; Crystallization; Gallium; Luminescence; Nanostructures; Nanowires; Particle Size; Silicon; Surface Properties

We combine the transient thermal grating and time-domain thermoreflectance techniques to characterize the anisotropic thermal conductivities of GaAs/AlAs superlattices from the same wafer. The transient grating technique is sensitive only to the in-plane thermal conductivity, while time-domain thermoreflectance is sensitive to the thermal conductivity in the cross-plane direction, making them a powerful combination to address the challenges associated with characterizing anisotropic heat conduction in thin films. We compare the experimental results from the GaAs/AlAs superlattices with first-principles calculations and previous measurements of Si/Ge SLs. The measured anisotropy is smaller than that of Si/Ge SLs, consistent with both the mass-mismatch picture of interface scattering and with the results of calculations from density-functional perturbation theory with interface mixing included.

Topics: Anisotropy; Arsenicals; Gallium; Hot Temperature; Molecular Weight; Nanostructures; Silicon; Thermal Conductivity

Monolithic integration of III-V optoelectronic devices with materials for various functionalities inexpensively is always desirable. Polysilicon (poly-Si) is an ideal platform because it is dopable and semiconducting, and can be deposited and patterned easily on a wide range of low cost substrates. However, the lack of crystalline coherency in poly-Si poses an immense challenge for high-quality epitaxial growth. In this work, we demonstrate, for the first time, direct growth of micrometer-sized InGaAs/GaAs nanopillars on polysilicon. Transmission electron microscopy shows that the micrometer-sized pillars are single-crystalline with pure wurzite-phase, far exceeding the substrate crystal grain size ~100 nm. The high quality growth is enabled by the unique tapering geometry at the base of the nanostructure, which reduces the effective InGaAs/Si contact area to <40 nm in diameter. The small footprint not only reduces stress due to lattice mismatch but also prevents the nanopillar from nucleating on multiple Si crystal grains. This relaxes the grain size requirement for poly-Si, potentially reducing the cost for poly-Si deposition. Lasing is achieved in the as-grown pillars under optical pumping, attesting their excellent crystalline and optical quality. These promising results open up a pathway for low-cost synergy of optoelectronics with other technologies such as CMOS integrated circuits, sensing, nanofluidics, thin film transistor display, photovoltaics, and so forth.

Topics: Arsenicals; Crystallization; Gallium; Indium; Lasers; Nanostructures; Optics and Photonics; Polymers; Silicon; Surface Properties

Free-standing semiconductor nanowires in combination with advanced gate-architectures hold an exceptional promise as miniaturized building blocks in future integrated circuits. However, semiconductor nanowires are often corrupted by an increased number of close-by surface states, which are detrimental with respect to their optical and electronic properties. This conceptual challenge hampers their potentials in high-speed electronics and therefore new concepts are needed in order to enhance carrier mobilities. We have introduced a novel type of core-shell nanowire heterostructures that incorporate modulation or remote doping and hence may lead to high-mobility electrons. We demonstrate the validity of such concepts using inelastic light scattering to study single modulation-doped GaAs/Al0.16Ga0.84As core-multishell nanowires grown on silicon. We conclude from a detailed experimental study and theoretical analysis of the observed spin and charge density fluctuations that one- and two-dimensional electron channels are formed in a GaAs coaxial quantum well spatially separated from the donor ions. A total carrier density of about 3 × 10(7) cm(-1) and an electron mobility in the order of 50,000 cm(2)/(V s) are estimated. Spatial mappings of individual GaAs/Al0.16Ga0.84As core-multishell nanowires show inhomogeneous properties along the wires probably related to structural defects. The first demonstration of such unambiguous 1D- and 2D-electron channels and the respective charge carrier properties in these advanced nanowire-based quantum heterostructures is the basis for various novel nanoelectronic and photonic devices.

Topics: Arsenicals; Crystallization; Electrons; Gallium; Nanotechnology; Nanowires; Quantum Dots; Semiconductors; Silicon

In this paper we present GaInAsSb photodiodes heterogeneously integrated on SOI by BCB adhesive bonding for operation in the short-wave infrared wavelength region. Photodiodes using evanescent coupling between the silicon waveguide and the III-V structure are presented, showing a room temperature responsivity of 1.4A/W at 2.3 µm. Photodiode structures using a diffraction grating to couple from the silicon waveguide layer to the integrated photodiode are reported, showing a responsivity of 0.4A/W at 2.2 µm.

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Infrared Rays; Light; Photometry; Refractometry; Scattering, Radiation; Semiconductors; Silicon; Surface Plasmon Resonance; Systems Integration

We report novel indium gallium arsenide (InGaAs) nanopillar lasers that are monolithically grown on (100)-silicon-based functional metal-oxide-semiconductor field effect transistors (MOSFETs) at low temperature (410 °C). The MOSFETs maintain their performance after the nanopillar growth, providing a direct demonstration of complementary metal-oxide-semiconudctor (CMOS) compatibility. Room-temperature operation of optically pumped lasers is also achieved. To our knowledge, this is the first time that monolithically integrated lasers and transistors have been shown to work on the same silicon chip, serving as a proof-of-concept that such integration can be extended to more complicated CMOS integrated circuits.

Topics: Arsenicals; Crystallization; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Lasers; Nanotechnology; Silicon; Transistors, Electronic

We report the first room-temperature continuous-wave operation of III-V quantum-dot laser diodes monolithically grown on a Si substrate. Long-wavelength InAs/GaAs quantum-dot structures were fabricated on Ge-on-Si substrates. Room-temperature lasing at a wavelength of 1.28 μm has been achieved with threshold current densities of 163 A/cm(2) and 64.3 A/cm(2) under continuous-wave and pulsed conditions for ridge-waveguide lasers with as cleaved facets, respectively. The value of 64.3 A/cm(2) represents the lowest room-temperature threshold current density for any kind of laser on Si to date.

Topics: Arsenicals; Crystallization; Electric Conductivity; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Lasers, Semiconductor; Materials Testing; Quantum Dots; Silicon

GaAs is grown by metal-organic vapor-phase epitaxy on a 55 nm round-hole patterned Si substrate with SiO(2) as a mask. The threading dislocations, which are stacked on the lowest energy facet plane, move along the SiO(2) walls, reducing the number of dislocations. The etching pit density of GaAs on the 55 nm round-hole patterned Si substrate is about 3.3 × 10(5) cm(-2). Compared with the full width at half maximum measurement from x-ray diffraction and photoluminescence spectra of GaAs on a planar Si(001) substrate, those of GaAs on the 55 nm round-hole patterned Si substrate are reduced by 39.6 and 31.4%, respectively. The improvement in material quality is verified by transmission electron microscopy, field-emission scanning electron microscopy, Hall measurements, Raman spectroscopy, photoluminescence, and x-ray diffraction studies.

Topics: Arsenicals; Crystallization; Gallium; Macromolecular Substances; Materials Testing; Molecular Conformation; Molecular Imprinting; Nanostructures; Nanotechnology; Particle Size; Porosity; Silicon; Silicon Dioxide; Surface Properties

Monolithic integration of III-V compound semiconductor devices with silicon CMOS integrated circuits has been hindered by large lattice mismatches and incompatible processing due to high III-V epitaxy temperatures. We report the first GaAs-based avalanche photodiodes (APDs) and light emitting diodes, directly grown on silicon at a very low, CMOS-compatible temperature and fabricated using conventional microfabrication techniques. The APDs exhibit an extraordinarily large multiplication factor at low voltage resulting from the unique needle shape and growth mode.

Topics: Arsenicals; Crystallization; Equipment Design; Equipment Failure Analysis; Gallium; Lighting; Nanostructures; Nanotechnology; Particle Size; Photometry; Semiconductors; Silicon; Systems Integration

We fabricated a novel lateral-current-injection-type distributed feedback (DFB) laser with amorphous-Si (a-Si) surface grating as a step to realize membrane lasers. This laser consists of a thin GaInAsP core layer grown on a semi-insulating InP substrate and a 30-nm-thick a-Si surface layer for DFB grating. Under a room-temperature continuous-wave condition, a low threshold current of 7.0 mA and high efficiency of 43% from the front facet were obtained for a 2.0-μm stripe width and 300-μm cavity length. A small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA.

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Feedback; Gallium; Indium; Lasers; Membranes, Artificial; Phosphines; Refractometry; Silicon

A GaAs-based surface-normal optical modulator using the free-carrier effect is demonstrated for the first time to our knowledge. The device exhibits ~43% modulation depth compared to 24% for a previously demonstrated Si-based device with twice the interaction length. Simulations predict ~1.8 times the speeds for GaAs-based devices compared to Si. Operation in conjunction with a supercontinuum source is used to characterize the wavelength response of the modulator. Potential for colorless operation makes the modulator a candidate for wavelength-division multiplexed networks with broadband light sources.

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Gallium; Lasers; Optical Devices; Silicon; Telecommunications

We report on single rolled-up microtubes integrated with silicon-on-insulator waveguides. Microtubes with diameters of ~7 μm, wall thicknesses of ~250 nm, and lengths greater than 100 μm are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from the handling GaAs substrate. The microtubes are then transferred from their host substrate to silicon-on-insulator waveguides by an optical fiber abrupt taper. The Q-factor of the waveguide coupled microtube is measured to be 1.5×10(5), the highest recorded for a semiconductor microtube cavity to date. The insertion loss and extinction ratio of the microtube are 1 dB and 34 dB respectively. By pumping the microtube with a 635 nm laser, the resonance wavelength is shifted by 0.7 nm. The integration of InGaAs/GaAs microtubes with silicon-on-insulator waveguides provides a simple, low loss, high extinction passive filter solution in the C+L band communication regime.

Topics: Arsenicals; Fiber Optic Technology; Gallium; Indium; Lasers; Quantum Dots; Semiconductors; Silicon; Telecommunications

We report on the one-dimensional (1D) heteroepitaxial growth of In(x)Ga(1-x)As (x = 0.2-1) nanowires (NWs) on silicon (Si) substrates over almost the entire composition range using metalorganic chemical vapor deposition (MOCVD) without catalysts or masks. The epitaxial growth takes place spontaneously producing uniform, nontapered, high aspect ratio NW arrays with a density exceeding 1 × 10(8)/cm(2). NW diameter (∼30-250 nm) is inversely proportional to the lattice mismatch between In(x)Ga(1-x)As and Si (∼4-11%), and can be further tuned by MOCVD growth condition. Remarkably, no dislocations have been found in all composition In(x)Ga(1-x)As NWs, even though massive stacking faults and twin planes are present. Indium rich NWs show more zinc-blende and Ga-rich NWs exhibit dominantly wurtzite polytype, as confirmed by scanning transmission electron microscopy (STEM) and photoluminescence spectra. Solar cells fabricated using an n-type In(0.3)Ga(0.7)As NW array on a p-type Si(111) substrate with a ∼ 2.2% area coverage, operates at an open circuit voltage, V(oc), and a short circuit current density, J(sc), of 0.37 V and 12.9 mA/cm(2), respectively. This work represents the first systematic report on direct 1D heteroepitaxy of ternary In(x)Ga(1-x)As NWs on silicon substrate in a wide composition/bandgap range that can be used for wafer-scale monolithic heterogeneous integration for high performance photovoltaics.

Topics: Arsenicals; Electromagnetic Fields; Gallium; Indium; Light; Materials Testing; Nanostructures; Particle Size; Silicon

InGaAs PIN photodetectors heterogeneously integrated on silicon-on-insulator waveguides are fabricated and characterized. Efficient evanescent coupling between silicon-on-insulator waveguides and InGaAs photodetectors is achieved. The fabricated photodetectors can work well without external bias and have a very low dark current of 10pA. The measured responsivity of a 40microm-long photodetector is 1.1A/W (excluding the coupling loss between the fiber and the SOI waveguide) at a wavelength of 1550nm and shows good linearity for an input power range of 40dB. Due to the large absorption coefficient of InGaAs and the efficient evanescent coupling, the fabricated photodetectors can cover the whole S, C and L communication bands.

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Light; Photometry; Refractometry; Semiconductors; Silicon; Systems Integration

We model and compare the thermal conductivity of rough semiconductor nanowires (NWs) of Si, Ge, and GaAs for thermoelectric devices. On the basis of full phonon dispersion relations, the effect of NW surface roughness on thermal conductivity is derived from perturbation theory and appears as an efficient way to scatter phonons in Si, Ge, and GaAs NWs with diameter D < 200 nm. For small diameters and large root-mean-square roughness Delta, thermal conductivity is limited by surface asperities and varies quadratically as (D/Delta)(2). At room temperature, our model previously agreed with experimental observations of thermal conductivity down to 2 W m(-1) K(-1) in rough 56 nm Si NWs with Delta = 3 nm. In comparison to Si, we predict here remarkably low thermal conductivity in Ge and GaAs NWs of 0.1 and 0.4 W m(-1) K(-1), respectively, at similar roughness and diameter.

Topics: Arsenicals; Computer Simulation; Gallium; Germanium; Models, Chemical; Nanotechnology; Nanowires; Semiconductors; Silicon; Surface Properties; Temperature; Thermal Conductivity

We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.

Topics: Aluminum; Arsenicals; Crystallization; Equipment Design; Equipment Failure Analysis; Gallium; Lighting; Materials Testing; Nanostructures; Nanotechnology; Particle Size; Semiconductors; Silicon

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate by metal-organic chemical vapor deposition and layer-transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380-nm-thick Au-Ge-Ni alloy layer. This broad-area Fabry-Perot laser exhibits InAs quantum dot ground state lasing at 1.31 microm at room temperature with a threshold current density of 600 A/cm(2).

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Lasers, Solid-State; Quantum Dots; Silicon

Au free GaAs nanowires with zinc blende structure, free of twin planes and with remarkable aspect ratios, have been grown on (111) Si substrates by molecular beam epitaxy. Nanowires with diameters down to 20 nm are obtained using a thin native oxide layer on the Si substrates. We discuss how the structural phase distribution along the wire length is controlled by the effective V/III ratio and temperature at the growth interface and explain how to obtain a pure twin plane free zinc blende structure.

Topics: Arsenicals; Catalysis; Crystallization; Gallium; Macromolecular Substances; Materials Testing; Molecular Conformation; Nanostructures; Particle Size; Phase Transition; Silicon; Surface Properties

A thin-film InGaAs/GaAs edge-emitting single-quantum-well laser has been integrated with a tapered multimode SU-8 waveguide onto an Si substrate. The SU-8 waveguide is passively aligned to the laser using mask-based photolithography, mimicking electrical interconnection in Si complementary metal-oxide semiconductor, and overlaps one facet of the thin-film laser for coupling power from the laser to the waveguide. Injected threshold current densities of 260A/cm(2) are measured with the reduced reflectivity of the embedded laser facet while improving single mode coupling efficiency, which is theoretically simulated to be 77%.

Topics: Arsenicals; Equipment Design; Gallium; Indium; Lasers; Light; Optics and Photonics; Semiconductors; Silicon; Silicon Dioxide

Micropatterned hydrogel stamps soaked in appropriate chemical etchants can imprint various types of micro- and nanoarchitectures into metals, conductive oxides, semiconductors, glasses, and crystals. Localized etching is mediated by a reaction-diffusion process initiated from the stamp microfeatures and gives lateral resolution down to approximately 300 nm. The method is well suited for the rapid prototyping of small-scale devices including multilevel microfluidic systems and curvilinear optical elements.

Topics: Arsenicals; Diffusion; Gallium; Hydrogels; Molecular Imprinting; Nanoparticles; Silicon; Tin Compounds; Zinc Oxide

Room temperature, continuous-wave lasing in a quantum dot photonic crystal nanocavity on a Si substrate has been demonstrated by optical pumping. The laser was an air-bridge structure of a two-dimensional photonic crystal GaAs slab with InAs quantum dots inside on a Si substrate fabricated through wafer bonding and layer transfer. This surface-emitting laser exhibited emission at 1.3 microm with a threshold absorbed power of 2 microW, the lowest out of any type of lasers on silicon.

Topics: Arsenicals; Computer-Aided Design; Equipment Design; Equipment Failure Analysis; Gallium; Indium; Lasers, Semiconductor; Nanotechnology; Quantum Dots; Reproducibility of Results; Sensitivity and Specificity; Silicon; Temperature

The monolithic integration of epitaxially-grown InGaAs/GaAs self-organized quantum dot lasers with hydrogenated amorphous silicon (a:Si-H) waveguides on silicon substrates is demonstrated. Hydrogenated amorphous silicon waveguides, formed by plasma-enhanced-chemical-vapor deposition (PECVD), exhibit a propagation loss of approximately 10 dB/cm at a wavelength of 1.05 microm. The laser-waveguide coupling, with coupling coefficient of 22%, is achieved through a 3.2 microm-width groove etched by focused-ion-beam (FIB) milling which creates high-quality etched GaAs facets.

Topics: Arsenicals; Equipment Design; Equipment Failure Analysis; Fiber Optic Technology; Gallium; Hydrogen; Indium; Lasers, Semiconductor; Quantum Dots; Silicon; Systems Integration

GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor-liquid-solid (VLS) growth in a solid source molecular beam epitaxy system. Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along <111> directions on both Si substrates for growth conditions investigated. The GaAs nanowires had a very uniform diameter along the growth direction. X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs<111> nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende. Current-voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy.

Topics: Arsenicals; Crystallography, X-Ray; Gallium; Microscopy, Electron, Scanning; Nanowires; Silicon

Topics: Arsenicals; Biocompatible Materials; Electrochemistry; Electrodes; Electrons; Gallium; Microscopy, Electron, Scanning; Nanowires; Plastics; Polyethylene Terephthalates; Silicon; Transistors, Electronic

Patterning of semiconductor surfaces is an area of intense interest, not only for technological applications, such as molecular electronics, sensing, cellular recognition, and others, but also for fundamental understanding of surface reactivity, general control over surface properties, and development of new surface reactivity. In this communication, we describe the use of self-assembling block copolymers to direct semiconductor surface chemistry in a spatially defined manner, on the nanoscale. The proof-of-principle class of reactions evaluated here is galvanic displacement, in which a metal ion, M+, is reduced to M0 by the semiconductor, including Si, Ge, InP, and GaAs. The block copolymer chosen has a polypyridine block which binds to the metal ions and brings them into close proximity with the surface, at which point they undergo reaction; the pattern of resulting surface chemistry, therefore, mirrors the nanoscale structure of the parent block copolymer. This chemistry has the added advantage of forming metal nanostructures that result in an alloy or intermetallic at the interface, leading to strongly bound metal nanoparticles that may have interesting electronic properties. This approach has been shown to be very general, functioning on a variety of semiconductor substrates for both silver and gold deposition, and is being extended to organic and inorganic reactions on a variety of conducting, semiconducting, and insulating substrates.

Topics: Arsenicals; Gallium; Germanium; Indium; Molecular Structure; Nanostructures; Phosphines; Polymers; Semiconductors; Silicon; Surface Properties

Topics: Arsenicals; Gallium; Gold; Indium; Ions; Metal Nanoparticles; Metals; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Nanostructures; Nanotechnology; Nitrogen; Phosphines; Semiconductors; Silicon; Surface Properties; Surface-Active Agents

The alloy GaN(x) As(1-x) (with x typically less than 0.05) is a novel semiconductor that has many interesting electronic properties because of the nitrogen-induced dramatic modifications of the conduction band structure of the host material (GaAs). Here we demonstrate the existence of an entirely new effect in the GaN(x) As(1-x) alloy system in which the Si donor in the substitututional Ga site (Si(Ga)) and the isovalent atom N in the As sublattice (N(As)) passivate each other's electronic activity. This mutual passivation occurs in Si-doped GaN(x) As(1-x) through the formation of nearest-neighbour Si(Ga) -N(As) pairs and is thermally stable up to 950 degrees C. Consequently, Si doping in GaN(x) As(1-x) under equilibrium conditions results in a highly resistive GaN(x) As(1-x) layer with the fundamental bandgap governed by a net 'active' N, roughly equal to the total N content minus the Si concentration. Such mutual passivation is expected to be a general phenomenon for electrically active dopants and localized state impurities that can form nearest-neighbour pairs.

Topics: Alloys; Arsenic; Arsenicals; Crystallization; Crystallography; Electric Impedance; Gallium; Materials Testing; Nitrogen; Semiconductors; Sensitivity and Specificity; Silicon; Temperature

The quality of GaAs layer on the Si substrate under different growth conditions with HWE technology was studied by Raman and PL spectra. The results show that the ratio of peak value to area for the TO peak at 265 cm-1 increased gradually with the improvement of the GaAs crystallinity quality for the GaAs layer at 300 K. The FWHM of Raman spectra of TO peak at 265 cm-1 is narrow, and the Raman shift is 2 cm-1. In the PL spectra, the FWHM at 900 nm is narrow. Then the results show GaAs layer is highly structural quality. But if we can not measure the PL peak at 900 nm, or the FWHM of Raman spectra of TO peak at 265 cm-1 is not narrow, the GaAs layer is not crystallinity. Therefore, we can estimate the layer quality by Raman and PL spectra.

Topics: Arsenicals; Gallium; Luminescence; Photochemistry; Quality Control; Scattering, Radiation; Silicon; Spectrometry, Fluorescence; Spectrum Analysis, Raman