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AlGaAs/GaAs/AlGaAs double-heterostructures having two-dimensional electron and hole channels at the respective interfaces are studied by measuring their photocurrent and photoluminescence characteristics. Under the weak photoexcitation, it is found that photo-generated electrons and holes are driven by a built-in electric field between the two channels and flow out mostly as a photocurrent to the respective electrodes, making the photoluminescence negligibly small. When the excitation reaches a certain level, some of photo-generated electrons and holes accumulate in each channel and weaken the built-in field, leading to an exponential increase in photoluminescence or the radiative recombination of electrons and holes. When the excitation gets strong, photo-generated carriers are lost mostly in the form of photoluminescence, resulting in the saturation of photocurrent. A theoretical model to explain these findings is presented. A possibility of using this type of study to clarify operating mechanisms of super-junction devices is suggested. [ABSTRACT FROM AUTHOR]

The linear (LPGE) and circular photogalvanic effects (CPGE), induced by interband (532 nm) and intersubband (1064 nm) excitation, have been investigated in a temperature range from 77 to 300K in GaAs/AlGaAs two-dimensional electron gas. The temperature dependences of the CPGE current induced by Rashba and Dresselhaus spin orbit coupling (SOC) under the interband and intersubband excitation are obtained, respectively. It is revealed that the CPGE and LPGE current induced by the intersubband excitation almost increases with increasing temperature, while that induced by interband excitation nearly decreases with increasing temperatures. These phenomena may be attributed to the different variation trends of photo-induced carrier density and SOC with increasing temperatures between interband and intersubband excitation. The evolutions of the ratio of the Rashba and Dresselhaus SOC (RD ratios) and the anisotropic ratio of linear photogalvanic tensors, corresponding to the interband and intersubband excitations, with temperatures are determined. The power dependence of CPGE and LPGE current induced by intersubband excitation is also investigated. It is found that for the power range from 0 to 275 mW, the CPGE current nearly increases linearly with increasing power, while the LPGE current shows a decreasing generation rate at higher power. This study also provides a method to manipulate the photogalvanic effects by temperatures and by using excitation light of different wavelengths. [ABSTRACT FROM AUTHOR]

We report photoluminescence (PL) characterization and model simulation of AlInAs/AlGaAs type-II quantum dots (QDs). A thorough and precise determination of the band parameters for QD and matrix materials is given, focusing on the effects of alloy composition and strain state on the electronic properties. Origins of experimentally observed PL emission peaks are identified through a comparison with the band lineup theoretically determined in this work. We interpret the QD emission as originating from indirect type-II transitions involving electrons in the barrier X valley and heavy holes with S and P symmetry. [ABSTRACT FROM AUTHOR]

A scheme of enhanced Goos-Hänchen (GH) shifts in reflected and transmitted light beams is exploited in a cavity, where an asymmetric double AlGaAs/GaAs quantum well structure with resonant tunneling to a common continuum is employed as the intracavity medium. With the help of Fano-type interference induced by resonant tunneling, the generated GH shifts that contain a negative lateral shift in reflected light beam and a positive lateral shift in transmitted light beam are found to be significantly enhanced. More interestingly, these GH shifts in reflected and transmitted light beams are modulated by means of a control beam and external bias voltage, in which maximum negative shift of 1.86mm and positive shift of 0.37mm are achievable. [ABSTRACT FROM AUTHOR]

Dynamic characteristics of low-voltage AlGaAs/GaAs heterostructure N-p-N phototransistors operating in the high-current mode have been studied. It was found that, above critical voltages, the turn-on process of a phototransistor consists of two phases separated in space and time. It is shown that the power of an optical-activation source affects the turn-on delay of the phototransistor and has no effect on the maximum current. An analysis of the spatial current dynamics in the plane of the collector p-n junction demonstrated that the first phase of the turn-on process is localized in the optical activation (optical window) region. In this case, the region of current localization during the first phase may be smaller than the optical-activation region. It was found that the whole current during the second phase is localized at the boundary between the optical window and the ohmic contact. The turn-on delay of the second phase is associated with the carrier transport in the base layer from the optical-activation region to the boundary with the ohmic collector contact. [ABSTRACT FROM AUTHOR]

Room temperature, single mode, pulsed emission from two-section coupled cavity InGaAs/AlGaAs/GaAs quantum cascade laser fabricated by focused ion beam processing is demonstrated and analyzed. The single mode emission is centered at 1059.4 cm–1 (9.44 µm). A side mode suppression ratio of 43 dB was achieved. The laser exhibits a peak output power of 15 mW per facet at room temperature. The stable, single mode emission is observed within temperature tuning range, exhibiting shift at rate of 0.59 nm/K. [ABSTRACT FROM AUTHOR]

It is shown theoretically that a GaAs/AlGaAs laser diode design using an asymmetric waveguide structure and a bulk active layer (AL), located close to the p‐cladding, can provide high output power in a single, broad transverse mode for short‐wavelength (<0.9 μm, matching the spectral range of high efficiency of silicon photodetectors) pulsed emission in the nanosecond pulse duration region, typically <<100 ns. The dependences of the laser performance on the thickness of the AL and the cavity length are analysed. It is shown that the relatively thick bulk AL allows the of short cavity lengths (<1 mm), for achieving high pulsed power while maintaining a relatively low series resistance and a narrow far field. [ABSTRACT FROM AUTHOR]

In order to characterize magnetic field (B) tunable THz plasmonic detectors, spectroscopy experiments were carried out at liquid helium temperatures and high magnetic fields on devices fabricated on a high electron mobility GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a meander shape) or ungated. Spectra of a photovoltage generated by THz radiation were obtained as a function of B at a fixed THz excitation from a THz laser or as a function of THz photon frequency at a fixed B with a Fourier spectrometer. In the first type of measurements, the wave vector of magnetoplasmons excited was defined by geometrical features of samples. It was also found that the magnetoplasmon spectrum depended on the gate geometry which gives an additional parameter to control plasma excitations in THz detectors. Fourier spectra showed a strong dependence of the magnetoplasmon resonance amplitude on the conduction-band electron filling factor which was explained within a model of the electron gas heating with THz radiation. The study allows to define both the advantages and limitations of plasmonic devices based on high-mobility GaAs/AlGaAs heterostructures for THz detection at low temperatures and high magnetic fields. [ABSTRACT FROM AUTHOR]

Photothermal deflection technique (PTD) is used to investigate the effects of thermal annealing time on nonradiative recombination parameters i.e. nonradiative lifetime of minority carriers, electronic diffusion coefficient, and surface and interface recombination velocity of AlGaAsSb/GaSb laser structure. The extraction of the electronic parameters are performed by PTD technique through extensive modeling by fitting the experimental photothermal signal to the corresponding theoretical ones. We have found that nonradiative recombination parameters have been enhanced by annealing time. These results are very promising for improvement of active layer used for vertical-cavity surface-emitting lasers (VCSELs). [ABSTRACT FROM AUTHOR]

This paper reports the experimental and theoretical assessments of the optical characteristics of recently introduced vertically coupled microdisk resonators made by the selective oxidation of AlGaAs multilayer structures. Experimental measurements show that the Q-factors are in the 103–104 range for diameters ranging from 75 to $300~\mu \text{m}$. To establish the origins of this limited performance, a coupled-mode-theory-based model of the single-access-waveguide-coupled resonator system was developed. It includes features which are specific to oxide-based vertically coupled resonators, namely, losses toward the slab waveguide lying under the resonator and a coupling region with an asymmetric and multilayer structure. Setting this simulation tool required the proposal and validation of a general criterion to select an appropriate set of decomposition permittivity profiles to be able to accurately model the characteristics of these more complex couplers using the coupled-mode-theory approach. This theoretical development is generic and can be now deployed to simulate any device which includes multiwaveguide couplers with arbitrary piece-wise-constant profile of the dielectric permittivity. Exploiting this particular development and experimental measurements of the disk sidewall roughness and of the coupling lengths, the calculated and experimental Q-factors are found to be in good agreement and allow establishing that the current performance is limited by the scattering losses and the slab leakage losses for small- and large-diameter devices, respectively. [ABSTRACT FROM AUTHOR]

THz (QCLs) are promising large output power semiconductor‐based THz sources with narrow bandwidths and wide operating frequency ranges. However, the operating temperature of THz QCLs is still limited by the design of its active region. Matyas et al. (2012) theoretically predicted that AlGaAs/GaAs THz QCLs with higher optical gain could be obtained by introducing a variable barrier height structure (Matyas et al., J. Appl. Phys. 2012, 111, 103106). Based on the proposed variable barrier QC structure, we fabricate AlGaAs/GaAs three‐well type THz QCLs with an additional very thin second extraction barrier and a low barrier height emission barrier. With this device, we obtain lasing operation at 3.7 THz at a maximum operating temperature of 145 K. [ABSTRACT FROM AUTHOR]

A semiconductor-laser design is proposed in which parasitic recombination in the waveguide region is suppressed by means of double asymmetric barriers adjacent to the active region. Double asymmetric barriers block the undesirable transport of one type of charge carrier while allowing the transport of the other type of carrier. The spacer in the double asymmetric barrier can serve to compensate the elastic strain introduced by the barrier layers as well as to control the energy spectrum of charge carriers and, thus, the transmission coefficient. By the example of a laser with AlGaAs waveguide layers, it is shown that the design with double asymmetric barriers makes it possible to suppress undesirable electron transport by a factor of 4 in comparison to the design using single asymmetric barriers. [ABSTRACT FROM AUTHOR]

This article presents a new method to reduce the dark current and increase the avalanche gain in InAs avalanche photodiode (APD) by adding Al 0.84 Ga 0.16 As blocking layer. This photodiode has displayed a high avalanche gain around 400 in 8 V bias voltage. Furthermore, a very low dark current and low excess noise factor between 0.1 and 1.9 in a temperature of 180 K to 300 K is observed. Finally, in comparison with other devices, a considerable increase of the gain along with decrease in dark current is observed. [ABSTRACT FROM AUTHOR]

The possibility of fabricating hybrid metamorphic heterostructures for vertical-cavity surfaceemitting lasers working in the 1300-nm spectral range is demonstrated. The metamorphic semiconductor part of the heterostructure with a GaAs/AlGaAs distributed Bragg reflector and an active region based on InAlGaAs/InGaAs quantum wells is grown by molecular-beam epitaxy on a GaAs (100) substrate. The top dielectric mirror with a SiO/TaO distributed Bragg reflector is formed by magnetron sputtering. The spectra of the room-temperature microphotoluminescence of these vertical-cavity surface-emitting laser heterostructures are studied under 532-nm excitation in the power range of 0-70 mW (with a focused-beam diameter of ~1 μm). The superlinear dependence of the photoluminescence intensity on the excitation power, narrowing of the photoluminescence peaks, and a change in the modal composition may be indications of lasing. The results obtained give evidence that the technology of the metamorphic growth of heterostructures on GaAs substrates can be used for the fabrication of vertical-cavity surface-emitting lasers working in the 1300- nm spectral range. [ABSTRACT FROM AUTHOR]

In this paper, a 1310 nm InAlGaAs/InP multiple quantum well ridge waveguide FP laser with a built-in wavelength detuned band-pass filter has been fabricated and investigated in experiments. When compared to the reference FP laser fabricated in the same wafer, it is observed that the root-mean-square spectral width can be approximately reduced to half; and moreover, significant improvements on the transmission performances in terms of the power penalty at given transmission distance and the longest transmission distance at given bit error rate, have been achieved for the proposed laser at the same fabrication cost. [ABSTRACT FROM AUTHOR]

In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the acute effect of photobiomodulation therapy (PBM) on arterial pressure in hypertensive and normotensive rats with application in an abdominal region. Normotensive (2K) and hypertensive (2K-1C) wistar rats were treated with PBM. Systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP) and heart rate (HR) were measured before, during and after PBM application. The nitric oxide (NO) serum concentration was measured before and after PBM application. Vascular reactivity study was performed in isolated thoracic aortas. Aluminum gallium arsenide (GaAlAs) diode laser was used, at 660 nm wavelength and 100 mW optical output. The PBM application induced a decrease of SAP in 2K-1C rats. In 2K rats, the PBM application had no effect on SAP, DAP and MAP. Moreover, the magnitude of hypotensive effect was higher in 2K-1C than in 2K rats. The PBM application induced a decrease of HR in 2K-1C and 2K, with higher effect in 2K-1C rats. In 2K-1C, the hypotensive effect induced by PBM was longer than that obtained in 2K rats. PBM application induced an elevation of NO concentration in serum from 2K-1C and 2K rats, with higher effect in 2K-1C. In isolated aortic rings PBM effect is dependent of NO release, and is not dependent of nitric oxide synthase (NOS) activation. Our results indicate that the abdominal acute application of PBM at 660 nm is able to induce a long lasting hypotensive effect in hypertensive rats and vasodilation by a NO dependent mechanism. [ABSTRACT FROM AUTHOR]

GaAs/AlGaAs laser structures with InGaAs quantum wells are grown by metal-organic chemical vapor deposition (MOCVD) on exact Si(001) substrates and substrates inclined by 4° to the [011] axis with a relaxed Ge buffer layer, emitting in the transparency region of bulk silicon (the wavelength is longer than 1100 nm at room temperature). The threshold power densities of stimulated emission, observed for the structures grown on exact and inclined substrates are 45 and 37 kW/cm, respectively. [ABSTRACT FROM AUTHOR]

The modulation of polarized radiation by GaAs/AlGaAs structures with tunnel-coupled double quantum wells in a strong lateral electric field is studied. The spectra of the variation in the refractive index under a lateral electric field in the vicinity of the intersubband resonance are experimentally investigated. [ABSTRACT FROM AUTHOR]

To seek the effect of activation and recesiation mechanism of AlGaAs photocathode, Cs, O co-adsorption on Al 0.5 Ga 0.5 As (001) β 2 (2 × 4) surface was performed based on first-principle density functional theory (DFT) and Cs/O activation and recesiation experiment of AlGaAs photocathode were carried out. The adsorption energies, band structure, and total density of states were calculated and analyzed. Calculation results show that all the adsorption models are stable adsorption structures. As the Cs coverage increases, the work function of model is decreasing, which indicates that after Cs/O alternate activation, when supplement with Cs that is recesiation, electrons more easily escape to the vacuum. Finally, the photocurrents during activation and recesiation process were recorded by multi-information measurement system. Cs only adsorption is helpful for obtaining effective photoemission for AlGaAs photocathode, Cs/O co-adsorption could further enhance the ability of photoemission and recesiation can make the decayed quantum efficiency recover. [ABSTRACT FROM AUTHOR]

The optical reflection from periodic structures based on a semiconductor AlGaAs matrix containing 2D arrays of plasmonic AsSb nanoinclusions is studied. The number of nanoinclusion layers is 12 or 24, and the nominal spatial periods are 100 or 110 nm, respectively. In the experimental spectra of the optical reflection coefficient at normal incidence, we observe resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm (1.64 or 1.60 eV), depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reach 22 and 31% for the systems of 12 and 24 AsSb-AlGaAs layers, while the volume fraction of the nanoinclusions is much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifts according to Wulff-Bragg's law. Numerical simulation of the optical reflection spectra is performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers. [ABSTRACT FROM AUTHOR]

A novel AlGaAs/GaAs triple quantum well (QW) photodetector at 5- \mu \textm wavelength has been proposed. The photodetector is designed with a double-resonance condition to achieve short tunneling time and large electron escape probability. The interface optical phonon modes and the phonon-assisted electron transition rates have been calculated. The electron escape probability is as high as 0.8 in the proposed photodetector, which is over two times higher than traditional phonon-assisted tunneling devices. Compared with QW infrared photodetectors, the noise current of the photodetector can be reduced dramatically ( > 10^13 times at 77 K and >4000 times at 300 K). In addition, the effects of delta doping on the absorption coefficients and scattering times of the triple QW photodetector are also investigated in detail. Delta doping at the middle of the well is much more desirable than uniform doping, in order to achieve large escape probability and high absorption coefficient. [ABSTRACT FROM PUBLISHER]

Both an Al 0.3 Ga 0.7 As heterojunction in the p -type emitter and a bandgap-graded layer in the n -type light absorbing base were employed in the GaAs-based solar cells. The simulation by AFORS-HET (Helmholtz-Zentrum Berlin) confirmed that the Al 0.3 Ga 0.7 As heterojunction enhanced the open-circuit voltage ( V oc ) by ~2%, and the n -type bandgap grading increased the fill factor by ~1%, respectively. The increased power conversion efficiency by ~3% supported the simulation results. An additional efficiency gain was obtained by the shape optimization of the band bending in the 80-nm compositional profile, increasing V oc up to 1.103 V. The cell with the anti-reflective coating exhibited high performance with a power conversion efficiency of 28.7% under 1 sun illumination, close to the world record of 28.8%. [ABSTRACT FROM AUTHOR]

We report on an experimental investigation of gamma radiation effects on the electronic and optical properties in carbon delta-doping GaAs/AlGaAs High Electron Mobility Transistors (HEMT) structures. Photoluminescence measurements are used to determine the electron-hole relaxation processes in the GaAs channel. For global information on the carriers dynamics in the structures examined, we studied their interactions with the crystal lattice, thermal activation states defects, the energy level activation. Gamma radiation has changed the electronic and optical properties in GaAs/AlGaAs structures, especially the carriers thermal activation. [ABSTRACT FROM AUTHOR]

Photovoltaic laser-power converters for a wavelength of λ = 809 nm are developed and fabricated on the basis of single-junction AlGaAs/GaAs structures grown by metal-organic vapor-phase epitaxy. The parameters of the photovoltaic structure constituted by an optical 'window' and a cladding layer are optimized by mathematical simulation. Photovoltaic converters with areas of S = 10.2 and 12.2 mm and 4 cm are fabricated and studied. For photocells with S = 10.2 mm, the monochromatic efficiency (η) was 60% at a current density of 5.9 A/cm. A photovoltaic module with a working voltage of 4 V (η = 56.3% at 0.34 A/cm) is assembled. [ABSTRACT FROM AUTHOR]

Ohmic contacts of power AlGaAs/GaAs-based photovoltaic converters were studied, and a technique for their fabrication was developed. Effect of the doping level of the contact layer on the free-carrier density and the contact resistivity was examined. A technique for fabrication of 2- to 4-μm-thick ohmic contacts with electrochemical deposition of gold layers was studied. The effect of deposition modes on the surface morphology of ohmic contacts and their solidity and conductivity was revealed. [ABSTRACT FROM AUTHOR]

Photovoltaic characteristics of more than 20 types of AlGaAs-based light-emitting diodes operating in the 830- to 970-nm wavelength range have been considered. It is established that AlxGa1 - xAs semiconductor structures employed in these devices can also be used for manufacturing photovoltaic converters of monochromatic radiation with quite high efficiency. [ABSTRACT FROM AUTHOR]

Context: Incipient carious lesions are characterized by subsurface dissolution due to more fluoride ions in the 50-100 microns of the tooth's outer surface. Aims: To determine an optimal power setting for 810 nm aluminum gallium arsenide laser for caries inhibition. Materials and Methods: Fifty-four caries-free extracted teeth were sectioned mesiodistally. The samples were divided into 18 groups for each power setting being evaluated. Each group had six samples. The laser used is 810 nm aluminum gallium arsenide laser with power setting from 0.1 watts to 5 watts. Laser fluorescence based device was used to evaluate the effect of irradiation. Statistical Analysis Used: Paired "t" test, one-way analysis of variance (ANOVA), Tukey's post hoc test, and the Pearson's correlation test. Results: The paired t-test showed that there is minimum divergence from the control for 3.5 watts. Tukey's post hoc test also showed statistically significantly results for 3.5 watts. The Pearson's correlation test showed that there was negative correlation between the watts and irradiation. Conclusions: The power setting that gave statistically significant results was 3.5 watts. [ABSTRACT FROM AUTHOR]

Growth of single crystalline AlGaAs nanostructures was carried out on highly lattice mismatched sapphire substrate by metal organic vapor phase epitaxy technique without using any external catalyst. In situ deposited Ga droplets were used as catalyst for the growth of AlGaAs nanostructures. The effects of growth temperature and V/III ratio were studied in detail. The growth of nanowires required a careful optimization of the growth conditions. The formation of well-faceted nanostructures and nanowires with hexagonal cross-section were found to be influenced by the growth parameters. The growth of nanostructures proceeds via VS growth mechanism after the consumption of initial Ga droplets depending on the growth conditions. [ABSTRACT FROM AUTHOR]

We demonstrate the growth and single-mode lasing operation of GaAs-AlGaAs core-multishell nanowires (NW) with radial single and multiple GaAs quantum wells (QWs) as active gain media. When subject to optical pumping lasing emission with distinct s-shaped input-output characteristics, line width narrowing and emission energies associated with the confined QWs are observed. Comparing the low temperature performance of QW NW laser structures having 7 coaxial QWs with a nominally identical structure having only a single QW shows that the threshold power density reduces several-fold, down to values as low as ~2.4 kW/cm² for the multiple QW NW laser. This confirms that the individual radial QWs are electronically weakly coupled and that epitaxial design can be used to optimize the gain characteristics of the devices. Temperature-dependent investigations show that lasing prevails up to 300 K, opening promising new avenues for efficient III-V semiconductor NW lasers with embedded low-dimensional gain media. [ABSTRACT FROM AUTHOR]

We studied the growth of InAs/InGaP quantum dot (QD) solar cells with near ideal bandgaps for intermediate band solar cells. Using a solid-source molecular beam epitaxy system, the evolution of InAs QDs grown on an InGaP buffer layer was examined as a function of InAs coverage and growth temperature. QDs were initiated with defective clusters for InAs deposition as small as 0.3 monolayer. The cross diffusion of In atoms and As–P exchange between InAs and the InGaP buffer layer could be responsible for the formation of coherent QDs and large defective clusters. An AlGaAs interlayer was inserted between InAs and the InGaP buffer layer to prevent the surface exchange reactions between InAs and InGaP. As a result, InAs QDs with a density of 1×10 11 cm −2 have been demonstrated with stronger photoluminescence emission compared to those with the GaAs interlayer. This growth technique was applied to fabricate InAs/InGaP QD solar cells. Post-growth annealing treatment was also investigated to improve the performance of QD solar cells. [ABSTRACT FROM AUTHOR]

We report experimental studies of conductance and magnetoconductance of GaAs/AlGaAs quantum well structures where both wells and barriers are doped by acceptor impurity Be. Temperature dependence of conductance demonstrate a non-monotonic behavior at temperatures around 100 K. At small temperatures (less than 10 K) where the conductivity has a quasi-metallic character which is apparently related to weak localization within the impurity band near the Fermi level) we observed strong negative magnetoresistance at moderate magnetic field which crossed over to positive magnetoresistance at very strong magnetic fields and was completely suppressed with an increase of temperature. We ascribe these unusual features to effects of temperature and magnetic field on a degree of disorder. The temperature dependent disorder is related to charge redistribution between different localized states with an increase of temperature. The magnetic field dependent disorder is also related by charge redistribution between different centers, however in this case an important role is played by the doubly occupied states of the upper Hubbard band, their occupation being sensitive to magnetic field due to on-site spin correlations. The detailed theoretical model is present. [ABSTRACT FROM AUTHOR]

The maximum operating temperature reported so far for THz-QCLs is 200K. With the well-known degradation mechanism of thermally activated LO-phonon scattering, one straightforward strategy to improve their temperature performances is the use of diagonal structures in which the upper-to-lower state scattering time is lengthened. However, the effectiveness of this method for achieving room temperature operation remains to be demonstrated. Here, we studied the temperature degradation of highly diagonal GaAs/Al0.15GaAs THz-QCLs. By analyzing their output power dependence on temperature, we identified the physical mechanism that limits their performance to be thermally activated leakage into the continuum, as evidenced by the large activation energy of ~80meV extracted from the Arrhenius plot. This observation is further supported by a careful analysis of current-voltage characteristics, especially in regions of high biases. In order to significantly improve the temperature performances of diagonal THz-QCLs, this leakage should be eliminated. [ABSTRACT FROM AUTHOR]

Diode lasers are widely used in dental laser treatment, but little is known about their thermal effects on different titanium implant surfaces. This is a key issue because already a 10 °C increase over the normal body temperature can induce bone injury and compromise osseo-integration. The present study aimed at evaluating the temperature changes and surface alterations experienced by different titanium surfaces upon irradiation with a λ = 808 nm diode laser with different settings and modalities. Titanium discs with surfaces mimicking different dental implant surfaces including TiUnite and anodized, machined surfaces were laser-irradiated in contact and non-contact mode, and with and without airflow cooling. Settings were 0.5-2.0 W for the continuous wave mode and 10-45 μJ, 20 kHz, 5-20 μs for the pulsed wave mode. The results show that the surface characteristics have a marked influence on temperature changes in response to irradiation. The TiUnite surface, corresponding to the osseous interface of dental implants, was the most susceptible to thermal rise, while the machined surfaces, corresponding to the implant collar, were less affected. In non-contact mode and upon continuous wave emission, the temperature rose above the 50 °C tissue damage threshold. Scanning electron microscopy investigation of surface alterations revealed that laser treatment in contact mode resulted in surface scratches even when no irradiation was performed. These findings indicate that the effects of diode laser irradiation on implant surfaces depend on physical features of the titanium coating and that in order to avoid thermal or physical damage to implant surface the irradiation treatment has to be carefully selected. [ABSTRACT FROM AUTHOR]

We investigate the plasmon mode coupling and depolarization shifts in AlGaAs/GaAs asymmetric step quantum wells (ASQWs) of the two-subband model with the Bohm-Pine's random-phase approximation with and without an applied electric field. By adjusting the well geometry parameters and material composition systematically, various characteristics of plasmons in ASQWs are found for different asymmetric cases. We find that (i) the intersubband plasmon has a large negative dispersion in long wavelength limit; (ii) the step width related depolarization shift depends on the number of subbands in the deep well; and (iii) the influence of electric field effect on depolarization shift and the coupling of the two plasmon modes is quite asymmetric with its minimum at +8 kV/cm by changing the electrical field and the ASQW structure parameters. The coupling and decoupling of the intersubband and intrasubband plasmon modes can be realized by adjusting the polarity and the strength of the external electric field and changing the ASQW structure parameters. [ABSTRACT FROM AUTHOR]

The next generation infrared (IR) detection and imaging technology calls for very large-scale IR sensitive chips with non-compromised performance. IR up-converters based on mature III-V semiconductors are thought to be quite promising candidates. However, the up-converters and the corresponding up-conversion systems so far substantially fall behind traditional IR detectors in terms of device performance due to the more serious trade-off between responsivity and dark current. In this article, a cascade infrared up-converter (CIUP) is proposed. By employing cascade carrier transport, IR responsivity can be enhanced while dark current remains in fairly low level. For the fabricated 4-μm InGaAs/AlGaAs CIUP under 3.3V at 78K, the up-conversion efficiency of the system is 2.1 mW/W under 2.1 μW mid-infrared input. Both the up-converter and the up-conversion system are under background-limited infrared performance regime below 120 K. Taking shot noise as the main source of system noise, the CIUP system displays a higher detectivity than previous semiconductor up-converters at similar wavelengths, and thus possesses greater potential for future large-scale IR detection and imaging applications. [ABSTRACT FROM AUTHOR]

We report observation of strong light-matter coupling in an AlGaAs microcavity (MC) with an embedded single parabolic quantum well. The parabolic potential is achieved by varying aluminum concentration along the growth direction providing equally spaced energy levels, as confirmed by Brewster angle reflectivity from a reference sample without MC. It acts as an active region of the structure which potentially allows cascaded emission of terahertz (THz) light. Spectrally and time resolved pump-probe spectroscopy reveals characteristic quantum beats whose frequencies range from 0.9 to 4.5 THz, corresponding to energy separation between relevant excitonic levels. The structure exhibits strong stimulated nonlinear emission with simultaneous transition to weak coupling regime. The present study highlights the potential of such devices for creating cascaded relaxation of bosons, which could be utilized for THz emission. [ABSTRACT FROM AUTHOR]

We investigate the effect of the recombination current of p–i–n junction solar-cells. We develop a simple evaluation method of the recombination and diffusion current component of the solar-cells based on the measured three characteristic values: short circuit current, open circuit voltage, and fill factor without the knowledge in the details of the device structure. The advantage of the developed technique is its simplicity and wide applicability to various p–i–n junction solar-cells. We apply the method to GaAs bulk and AlGaAs/GaAs superlattice solar-cells. Obtained parameters well reproduce the whole current-voltage characteristics. The diode current is almost dominated by the recombination current at the maximum-output voltage for both GaAs bulk and superlattice cells. The higher contribution of the recombination current in the superlattice solar-cell is due to the quality of the AlGaAs barriers and the AlGaAs/GaAs interfaces. This result indicates that the good crystalline quality is important to enhance the efficiency of the solar-cells. [ABSTRACT FROM AUTHOR]

Nanoscale device fabrication has enabled remarkable scientific advances. Yet a single broken electrode can render a complex device useless. The authors consider local electron-beam-induced deposition (EBID) of platinum as a method for restoring function to devices with damaged gate electrodes. The authors find that platinum deposits written with EBID at low acceleration voltage (350?V) remain conductive down to millikelvin temperatures, if they are annealed after deposition in the presence of oxygen. The authors apply this technique to a complex quantum dot device based on a GaAs/AlGaAs heterostructure. [ABSTRACT FROM AUTHOR]

In this reported work, both high peak current density and high peak-to-valley current ratio (PVCR) in AlAs/GaAs triple-barrier quantum-well intraband resonant tunnelling diodes (TBQW IRTDs) were accomplished. The valley current density (JV) of TBQW IRTDs can be degraded as the barrier thickness reaches 4 nm thickness. This result suggests narrow barrier thickness is due to the slight band bending effect in the conduction band of i-AlAs barrier layers. The peak current density (JP) of the TBQW IRTDs will be <2.43 KA/cm2 as the i-AlAs barriers thickness of the TBQW IRTD reaches 5 nm thickness. The optimal thickness of barrier layers should be selected at 4 nm thickness to obtain the highest PVCR value (about 4270), in which the sample with barrier layers of 4 nm thickness possesses the lowest valley current density. [ABSTRACT FROM AUTHOR]

The study explored titanium dioxide (TiO 2 ) prepared by liquid phase deposition (LPD) deposited on (NH 4 ) 2 S x -treated aluminum gallium arsenide (AlGaAs), including the surface roughness by using atomic force microscopy (AFM) measurements and electrical properties. The leakage current density of MOS capacitor is approximately 6.83 × 10 −7 A/cm 2 at zero electric field for the sample without any pretreatment. The interface trap density ( D it ) and the flat-band voltage shift (Δ V FB ) are 4.46 × 10 12 cm −2 eV −1 and 3.6 V, respectively. After the 10 min 5% (NH 4 ) 2 S x pretreatment, the leakage current density, D it , and Δ V FB can be improved to 1.04 × 10 −7 A/cm 2 at zero electric field, 2.28 × 10 12 cm −2 eV −1 , and 2 V, respectively. The paper also demonstrates the application to the AlGaAs/InGaAs metal-oxide-semiconductor pseudomorphic high-electron-mobility transistor (MOS-PHEMT) using LPD-TiO 2 after 10 min sulfide pretreatment. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated enhanced spontaneous and stimulated emission of GaAs/AlGaAs nanowire via the Purcell effect. By integrating the NW and SiO2-Au substrate, the hybridization of the dielectric modes in the NW with surface plasmons on the surface of Au formed hybrid plasmonic modes. Taking advantage of the nanolocalized electromagnetic field of hybrid plasmonic modes, the intensities of spontaneous and stimulated emission were enhanced via the Purcell effect by factors of four and ten, respectively. More importantly, the plasmonic lasing action was continuous-wave under the continuous-wave pump. [ABSTRACT FROM AUTHOR]

We report a passively mode-locked (ML) Tm:YAP laser pumped by an 790 nm AlGaAs diode. With a semiconductor saturable absorber mirror (SESAM) as mode-locker, stable ML pulses is generated with pulse width of 1.89 ps, repetition rate of 97 MHz, and central wavelength of 1938 nm. The highest ML output power of 710 mW was obtained, to the best of our knowledge, this is the highest output power of SESAM based, Tm ion doped crystalline ML lasers. [ABSTRACT FROM AUTHOR]

GaInSb multiple quantum wells (MQW) grown on GaAs using an AlGaSb interface misfit (IMF) metamorphic buffer layer technique exhibit superior infrared photoluminescence (PL) at room temperature compared with MQW grown directly on GaSb. PL emission was obtained in the range from 1.7 μm (4 K) to 1.9 μm (300 K) from Ga1-xInxSb samples containing five compressively strained QW with In content x~0.3. Structural and optical characterisation confirms that the AlGaSb IMF growth technique is promising for the development of photonic devices operating at extended wavelengths based on GaAs substrates. [ABSTRACT FROM AUTHOR]

Indoor photovoltaic energy harvesting is a promising candidate to power millimeter (mm)-scale systems. The theoretical efficiency and electrical performance of photovoltaics under typical indoor lighting conditions are analyzed. Commercial crystalline Si and fabricated GaAs and Al0.2Ga0.8As photovoltaic cells were experimentally measured under simulated AM 1.5 solar irradiation and indoor illumination conditions using a white phosphor light-emitting diode to study the effects of input spectra and illuminance on performance. The Al0.2Ga0.8As cells demonstrated the highest performance with a power conversion efficiency of 21%, with open-circuit voltages >0.65 V under low lighting conditions. The GaAs and Al0.2Ga0.8As cells each provide a power density of $\sim 100$ nW/mm ^{2} or more at 250 lx, sufficient for the perpetual operation of present-day low-power mm-scale wireless sensor nodes. [ABSTRACT FROM PUBLISHER]

The high power microwave (HPM) induced effects in AlGaAs/InGaAs pseudomorphic high electron mobility transistors (pHEMTs) are investigated by simulation and experiments. Simulated results suggest that the HPM damage mechanism is device burnout, which is caused by emerging current path and strong electric field intensity beneath the gate metal. Besides, analysis points out that the gate metal diffusion may be thermally activated, resulting in DC and RF performance degradation. Specifically, a positive shift will occur to the pinch-off voltage while accordingly the small-signal gain will decrease. The HPM injection experiments on the dual-stage pHEMT low noise amplifiers (LNAs) are carried out. Experimental results substantiate that deterioration happens both in the noise figure and in the small-signal gain, which is in agreement with the simulated results. Failure analysis indicates that the HPM induced failure of LNA is attributed to the failure of the first stage pHEMT. Finally, samples dissection analysis using the scanning electron microscopy (SEM) verifies the simulation analysis of the damage mechanism and the location susceptible to burnout. Meanwhile, the assumption of gate metal diffusion is validated by the observation of pits after removing the gate metal. The performance parameters deterioration can be utilized as the degradation (or damage) criteria, and the mechanisms analysis facilitates making reinforcing design. [ABSTRACT FROM AUTHOR]

The intra-pulse measurements of the beam steering in an AlGaAs/GaAs quantum cascade laser are presented in this paper. The experimental results are explained by a two-mode theoretical model. The near field of the laser radiation is calculated according to the effective index method and transposed to the far field numerically according to Huygens principle. The maximal observed value of deflection of the beam has been found to be $$17^{\circ }$$ . For supply currents in the range from 1.6 to 2.4 times the threshold the beam steering occurs only on one side of the resonator axis, and stays is the same for all current values. For higher supply current, it occurs alternately on both sides and exhibits a bistability. The time period of the beam direction change has been found to be about 40 ns for the lowest current and was decreasing with the current increase to about 20 ns. [ABSTRACT FROM AUTHOR]

In this work, AlGaAs/GaAs superlattices with layer composition imitating the active region of quantum cascade lasers emitting in the mid infrared spectral range were investigated. Using optical spectroscopy techniques (photoreflectance and photoluminescence) together with numerical calculations performed within the effective mass approximation, we studied the band structure of the formed conduction minibands including the modification of the wave functions with the external electric field. In addition, the applied growth rates of the GaAs/AlGaAs superlattices have been verified by investigating the Stokes shift between the emission and absorption spectra. Finally, it has been shown that testing the structure imitating the operational laser device might be performed (without the electric field applied) by photoluminescence measurements realized within the Fourier Transformed Infrared Spectroscopy based concept. [ABSTRACT FROM AUTHOR]