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AlGaAs is promising absorber material for multi‐junction solar cells (MJSC) for its tunable bandgap to match various bandgap combination designs. However, the path to achieving high‐quality AlGaAs for solar cell application remains to be determined. In this study, we grow and characterize carbon‐doped p‐Al0.375Ga0.625As on exact and vicinal GaAs(0 0 1) substrates, using metal‐organic vapor phase epitaxy (MOVPE). Low‐temperature photoluminescence (PL) measurement is performed in the range from 6 K to 300 K. The Arrhenius plot of PL intensities reveals an increasing trend for non‐radiative recombination in conjunction with increasing miscut angle. The presence of atomic ordering that inversely correlates to the miscut angle is proposed to explain the PL linewidth and peak energy dependency on substrate orientation. The conflicting tendency of non‐radiative recombination and ordering with miscut angle are further validated using solar cell devices. A slightly vicinal substrate is recommended for AlGaAs solar cells according to our observation. [ABSTRACT FROM AUTHOR]

In GaAs-type materials, the primary mechanism for intra-valley scattering of low-energy electrons is their interaction with acoustic photons. These collisions are of the elastic and isotropic type, with their main effect being the nearly uniform scattering of the velocity vector of the electrons. Since the drift current in heterojunction bipolar transistors is proportional to the electric field, the contribution of the majority drift current cannot be neglected, as even a very small internal field produces a significant current when the number of carriers is very high. At the metallurgical heterojunction (x = 0), the total current is equal to the sum of the two thermionic emission components. The paper analyses the variation of the direct current of the Al0.3Ga0.7As/GaAs heterojunction, used as an emitter-base NP junction in heterojunction bipolar transistors, using the Python program. [ABSTRACT FROM AUTHOR]

The growth of thick (more than 50 μm) AlxGa1 –xAs gradient layers in the Al–Ga–As–Sn system has been modeled. Sn-doped AlxGa1 –xAs layers up to 85 μm thick were obtained by liquid-phase epitaxy. The obtained experimental profiles of the AlxGa1 –xAs composition gradient satisfy the used theoretical model for the cases of growth from a limited volume of a solution–melt. [ABSTRACT FROM AUTHOR]

Experimental methods are presented for determining the thermal resistance of vertical-cavity surfaceemitting lasers (VCSELs) and the lateral electrical conductivity of their p-type semiconductor layers. A VCSEL structure was manufactured from III-As compounds on a gallium arsenide substrate. Conductivity was determined using transmission line measurement (TLM). Electrical and thermal parameters were determined for various ambient temperatures. The results could be used for computer analysis of VCSELs. Keywords: TLM, thermal resistance, VCSEL, AlGaAs.

Photovoltaic multijunction power-converting III–V semiconductor devices generate electrical power from the optical energy of laser beams. They exhibit conversion efficiencies reaching values greater than 60% and 50% for the GaAs and the InP material systems, respectively. The applications of optical wireless power transmission and power-over-fiber greatly benefit from employing such laser power converters constructed with multiple subcells; each is designed with either thin GaAs or InGaAs absorber regions. This study elucidates how the application of electric fields on thin heterostructures can create specific current–voltage characteristics due to modifications of the absorption characteristics from Franz–Keldysh perturbations and the onset of quantum-confined Stark effects. Negative differential photocurrent behavior can be observed as the reverse bias voltage is increased, until the corresponding current-clamping subcell reaches its reverse breakdown condition. The reverse voltage breakdown characteristics of the subcells were also measured to depend on the thickness of the subcell and on the optical intensity. The onset of the reverse breakdown was found to be at ~2.0–2.5 V under illumination and the thinner subcells exhibited higher levels of reverse bias currents. These effects can produce distinctive current–voltage behavior under spectrally detuned operations affecting the thinner subcells' biases, but have no significant impact on the performance and maximum power point of multijunction power converters. [ABSTRACT FROM AUTHOR]

AlzGa1−zAs layers of various compositions were grown using metalorganic chemical vapor deposition on a GaAs substrate with a pattern of alternating SiO2 mask/window stripes, each 100 µm wide. Microphotoluminescence maps and thickness profiles of AlzGa1−zAs layers that demonstrated the distribution of the growth rate and z in the window were experimentally studied. It was shown that the layer growth rate and the AlAs mole fraction increased continuously from the center to the edge of the window. It was experimentally shown that for a fixed growth time of 10 min, as z increased from 0 to 0.3, the layer thickness difference between the center of the window and the edge increased from 700 Å to 1100 Å, and the maximum change in z between the center of the window and the edge reached Δz 0.016, respectively. Within the framework of the vapor -phase diffusion model, simulations of the spatial distribution of the layer thickness and z across the window were carried out. It was shown that the simulation results were in good agreement with the experimental results for the effective diffusion length D/k: Ga—85 µm, Al—50 µm. [ABSTRACT FROM AUTHOR]

Experimental methods are presented for determining the thermal resistance of vertical-cavity surfaceemitting lasers (VCSELs) and the lateral electrical conductivity of their p-type semiconductor layers. A VCSEL structure was manufactured from III-As compounds on a gallium arsenide substrate. Conductivity was determined using transmission line measurement (TLM). Electrical and thermal parameters were determined for various ambient temperatures. The results could be used for computer analysis of VCSELs. [ABSTRACT FROM AUTHOR]

This paper investigates the possibility of using a nanolaminate TiO2/Ag/TiO2 structure as a transparent conductive coating on GaAs solar cells. A novel result is that this structure forms an Ohmic contact to Al-rich AlGaAs, which is used as a "window" layer in GaAs-based solar cells. The TiO2/Ag/TiO2 structure is deposited by RF magnetron sputtering at room temperature. This nanolaminate coating has good optical and electrical properties: a high transmittance of 94% at 550 nm, a sheet resistance of 7 Ω/sq, and a figure of merit (FOM) of 105 × 10−3 Ω−1. These properties are the result of the presence of a discontinuous layer of Ag between two thin layers of TiO2. The morphology of a discontinuous layer of Ag nanogranules is confirmed by the observation of a cross-section of a sample with high-resolution transmission electron microscopy (HRTEM) and EDX analyses. Current–voltage diode characteristics of GaAs solar cells measured under standard test illumination at 1000 W/m2 are analyzed. The formation of an Ohmic contact is explained by the Fermi-level pinning effect caused by nanosized Ag particles in the nanolaminate TiO2/Ag/TiO2 structure. The obtained results demonstrate a new application of oxide−metal−oxide (OMO) coatings as Ohmic contacts to III-V compound semiconductors. [ABSTRACT FROM AUTHOR]

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices relies on surface gates which impose strong limitations on the maximum distance from the surface where the confining electrostatic potentials can be engineered. Surface gates also introduce strain fields which cause imperfections in the semiconductor crystal structure. Another way to create confining electrostatic potentials inside semiconductors is by means of light and photosensitive dopants. Light can be structured in the form of perfectly parallel sheets of high and low intensity which can penetrate deep into a semiconductor and, importantly, light does not deteriorate the quality of the semiconductor crystal. In this work, we employ these important properties of structured light to form metastable states of photo-sensitive impurities inside a GaAs/AlGaAs quantum well structure in order to create persistent periodic electrostatic potentials at large predetermined distances from the sample surface. The amplitude of the light-induced potential is controlled by gradually increasing the light fluence at the sample surface and simultaneously measuring the amplitude of Weiss commensurability oscillations in the magnetoresistivity. [ABSTRACT FROM AUTHOR]

The effect of active and passive power supply modes on the resistance of light-emitting diodes (LEDs) fabricated on the basis of a multilayer AlGaAs heterostructure to irradiation by gamma quanta has been studied. For the LEDs under study, regardless of the power regime during irradiation, three characteristic stages of radiation power reduction were distinguished; in this case, the second stage is characterized by a higher damage factor, and the third stage is characterized by the appearance of catastrophic failures. During irradiation of LED in the active power mode, two differently directed processes of change in the radiation power are observed. It is assumed that the first process is due to a decrease in the LED radiation power owing to the introduction of the corresponding radiation defects. The second process is due to the partial restoration of the radiation power owing to radiation, radiation-thermal, and/or electrically stimulated annealing of a part of the created defects. The observed restoration of the radiation power in the active power supply mode of the LED during irradiation significantly increases its resistance to irradiation with gamma quanta. [ABSTRACT FROM AUTHOR]

In the paper, comparative studies of near-IR photoluminescence (PL) in structures with GaAs/AlGaAs quantum wells possessing different selective doping profiles have been performed. The PL spectra recorded at 5 K for different intensities of interband optical pumping were analyzed and main channels of radiative recombination were determined. The dependences of the main PL line intensities on the pump level were obtained. The results of the studies performed suggest that n-GaAs/AlGaAs nanostructures with the compensating acceptor impurity located not in the n-GaAs quantum well, but in its barriers, are preferable for terahertz radiation generation.

AlzGa1−zAs layers of various compositions were grown using metalorganic chemical vapor deposition on a GaAs substrate with a pattern of alternating SiO2 mask/window stripes, each 100 µm wide. Microphotoluminescence maps and thickness profiles of AlzGa1−zAs layers that demonstrated the distribution of the growth rate and z in the window were experimentally studied. It was shown that the layer growth rate and the AlAs mole fraction increased continuously from the center to the edge of the window. It was experimentally shown that for a fixed growth time of 10 min, as z increased from 0 to 0.3, the layer thickness difference between the center of the window and the edge increased from 700 Å to 1100 Å, and the maximum change in z between the center of the window and the edge reached Δz 0.016, respectively. Within the framework of the vapor -phase diffusion model, simulations of the spatial distribution of the layer thickness and z across the window were carried out. It was shown that the simulation results were in good agreement with the experimental results for the effective diffusion length D/k: Ga—85 µm, Al—50 µm.

In this work, we report the results of the compositional analysis of an aluminum gallium arsenide (AlGaAs) sample using the calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique. The AlGaAs sample was doped with three various concentrations of gallium (Ga), arsenic (As), and aluminum (Al), as reported by the manufacturer, and the CF-LIBS technique was employed to identify the doping concentration. A pulsed Q-switched Nd: YAG laser capable of delivering 200 and 400 mJ energy at 532 and 1064 nm, respectively, was focused on the target sample for ablation, and the resulting emission spectra were captured using a LIBS 2000+ spectrometer covering the spectral range from 200 to 720 nm. The emission spectra of the AlGaAs sample yielded spectral lines of Ga, As, and Al. These lines were further used to calculate the plasma parameters, including electron temperature and electron number density. The Boltzmann plot method was used to calculate the electron temperature, and the average electron temperature was found to be 5744 ± 500 K. Furthermore, the electron number density was calculated from the Stark-broadened line profile method, and the average number density was calculated to be 6.5 × 1017 cm−3. It is further observed that the plasma parameters including electron temperature and electron number density have an increasing trend with laser irradiance and a decreasing trend along the plume length up to 2 mm. Finally, the elemental concentrations in terms of weight percentage using the CF-LIBS method were calculated to be Ga: 94%, Al: 4.77% and As: 1.23% for sample-1; Ga: 95.63%, Al: 1.15% and As: 3.22% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The certified concentrations were Ga: 95%, Al: 3% and As: 2% for sample-1; Ga: 96.05%, Al: 1% and As: 2.95% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The concentrations measured by CF-LIBS showed good agreement with the certified values reported by the manufacturer. These findings suggest that the CF-LIBS technique opens up an avenue for the industrial application of LIBS, where quantitative/qualitative analysis of the material is highly desirable. [ABSTRACT FROM AUTHOR]

A design study is presented for an efficient, compact and robust device to convert the frequency of single-photons from the near-infrared to the telecom C-band. The material platform aluminum gallium arsenide (AlGaAs)-on-insulator, with its relatively large second-order nonlinearity, is used to create highly confined optical modes. This platform can feasibly incorporate single-photon emitters such as indium arsenide (InAs) on gallium arsenide (GaAs), paving the way towards direct integration of single-photon sources and nonlinear waveguides on the same chip. In this design study, single-pass difference-frequency generation (DFG) producing C-band single-photons is enabled via form birefringent phase-matching between a 930 nm single-photon pump and continuous wave (CW) idler at 2,325 nm. In particular the idler and single-photons are combined with an on-chip directional coupler, and then tapered to a single waveguide where the three modes are phase-matched. The design is studied at a special case, showing high fabrication tolerances, and an internal conversion efficiency up to 41%. [ABSTRACT FROM AUTHOR]

This paper investigates the possibility of using a nanolaminate TiO2/Ag/TiO2 structure as a transparent conductive coating on GaAs solar cells. A novel result is that this structure forms an Ohmic contact to Al-rich AlGaAs, which is used as a “window” layer in GaAs-based solar cells. The TiO2/Ag/TiO2 structure is deposited by RF magnetron sputtering at room temperature. This nanolaminate coating has good optical and electrical properties: a high transmittance of 94% at 550 nm, a sheet resistance of 7 Ω/sq, and a figure of merit (FOM) of 105 × 10−3 Ω−1. These properties are the result of the presence of a discontinuous layer of Ag between two thin layers of TiO2. The morphology of a discontinuous layer of Ag nanogranules is confirmed by the observation of a cross-section of a sample with high-resolution transmission electron microscopy (HRTEM) and EDX analyses. Current–voltage diode characteristics of GaAs solar cells measured under standard test illumination at 1000 W/m2 are analyzed. The formation of an Ohmic contact is explained by the Fermi-level pinning effect caused by nanosized Ag particles in the nanolaminate TiO2/Ag/TiO2 structure. The obtained results demonstrate a new application of oxide−metal−oxide (OMO) coatings as Ohmic contacts to III-V compound semiconductors.

This study offers an in-depth examination of aluminum gallium arsenide (AlGaAs) as a high-performance and durable material for photoelectrochemical water splitting, a key method of cost-effective renewable hydrogen production. Purpose-designed pin-AlGaAs photocathodes are demonstrated to yield a remarkable photocurrent density of over 15 mA/cm 2 and an impressive onset potential of 1.11 V vs RHE. These results significantly outperform those achieved with other materials, marking a considerable advancement in the field. Moreover, this work addresses the long-standing issue of AlGaAs corrosion in an aqueous electrolyte. An innovative approach using a 60 nm TiO 2 protection layer is introduced, providing substantial corrosion resistance in acidic environments and thereby enhancing material durability. This research also provides valuable insights into the role of passivation layers on charge transfer. It was found that an n-GaAs passivation layer further enhances the onset potential, whereas an n-InGaP layer contributes to a decline in the overall performance. These findings pave the way for new applications of AlGaAs in solar water splitting technology, offering a promising pathway toward the development of efficient AlGaAs/Si tandem water splitting devices.

As semiconductor devices approach dimensions at the atomic scale, controlling the compositional grading across heterointerfaces becomes paramount. Particularly in nanowire axial heterostructures, which are promising for a broad spectrum of nanotechnology applications, the achievement of sharp heterointerfaces has been challenging owing to peculiarities of the commonly used vapor-liquid-solid growth mode. Here, the grading of Al across GaAs/Al x Ga 1- x As/GaAs heterostructures in self-catalyzed nanowires is studied, aiming at finding the limits of the interfacial sharpness for this technologically versatile material system. A pulsed growth mode ensures precise control of the growth mechanisms even at low temperatures, while a semiempirical thermodynamic model is derived to fit the experimental Al-content profiles and quantitatively describe the dependences of the interfacial sharpness on the growth temperature, the nanowire radius, and the Al content. Finally, symmetrical Al profiles with interfacial widths of 2-3 atomic planes, at the limit of the measurement accuracy, are obtained, outperforming even equivalent thin-film heterostructures. The proposed method enables the development of advanced heterostructure schemes for a more effective utilization of the nanowire platform; moreover, it is considered expandable to other material systems and nanostructure types.

The transient optical response of multiresonant all‐dielectric nanoantennas via a combination of broadband ultrafast reflectivity experiments and nonlinear optics nanoscale modeling is studied. Ultrafast all‐optical control of the reflectivity is demonstrated in variably sized Al.18Ga.82As nanoantennas over four distinct Mie resonances (including Fano‐like resonances), spanning a broad spectral range, from the red to the near‐infrared. A spatially inhomogeneous dynamical model, which accounts for diffusion of the photogenerated carriers inside the semiconductor, is introduced and exploited to isolate the physical phenomena leading to the overall transient response, namely, Drude plasma formation and Pauli blocking following band filling and thermo‐optical effect. The results pave the way to the development of multiwavelength all‐optically reconfigurable filters for next‐generation ultrafast add/drop multiplexing.

The impact ionization characteristics of (AlxGa1-x)0.52In0.48P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ($\alpha $ and $\beta $ , respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of AlxGa1-xAs. While both $\alpha $ and $\beta $ initially decrease gradually with increasing bandgap, a sharp decrease in $\beta $ occurs in (AlxGa1-x)0.52In0.48P when ${x} > 0.61$ , while $\alpha $ decreases only slightly. $\alpha $ and $\beta $ decrease minimally with further increases in ${x}$ and the breakdown voltage saturates. This behavior is broadly similar to that seen in AlxGa1-xAs, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems. [ABSTRACT FROM AUTHOR]

The transient optical response of multiresonant all‐dielectric nanoantennas via a combination of broadband ultrafast reflectivity experiments and nonlinear optics nanoscale modeling is studied. Ultrafast all‐optical control of the reflectivity is demonstrated in variably sized Al.18Ga.82As nanoantennas over four distinct Mie resonances (including Fano‐like resonances), spanning a broad spectral range, from the red to the near‐infrared. A spatially inhomogeneous dynamical model, which accounts for diffusion of the photogenerated carriers inside the semiconductor, is introduced and exploited to isolate the physical phenomena leading to the overall transient response, namely, Drude plasma formation and Pauli blocking following band filling and thermo‐optical effect. The results pave the way to the development of multiwavelength all‐optically reconfigurable filters for next‐generation ultrafast add/drop multiplexing. [ABSTRACT FROM AUTHOR]

Luminescence properties of MOVPE grown AlGaAs epilayer on conventional GaAs (100) substrates have been unravelled through temperature dependent photoluminescence (PL) spectroscopy. A shrinkage of ∼33.3 meV in the excitonic energy as a result of the presence of the natural superlattice ordering has been reported. The temperature dependence of the excitonic energy has been investigated using two independent models, among which the two-oscillator model is found to give the best fit to the experimental data throughout the operating temperature range (4–150 K). The extracted phonon energies come out to be higher for the as-grown (ordered) sample relative to the annealed (disordered) sample which is a consequence of confinement due to the periodic modulation. From the analysis of the thermal quenching of the PL signal related to the excitonic transition using the modified Arrhenius equation, we have found that the thermalization of the carriers involve two non-radiative channels for the material. Among them, the one related to the defects, impurity, interface quality of the material is dominant at low temperature while the other relating the thermal escape of excitons from its bound state becomes dominant at high temperature. The thermal activation energies possess higher values for the as-grown sample which could be ascribed to the confinement of the carriers in the natural superlattice layers. These analyses gave a clear understanding of the role of electron-phonon interaction in the thermalization of carriers which results in band-gap shrinkage, sharp linewidth and enhanced PL signal for the natural superlattice sample due to localization of the carriers in the periodic structure in comparison to the annealed disordered one. The study revealed a better temperature stability of the luminescence of the material with periodic superlattice ordering. • Optical bandgap shrinkage of ∼33 meV due to natural superlattice ordering in AlGaAs. • Variation of PL peak energy, linewidth and intensity fitted with model equations. • Thermalization of the carriers involve two non-radiative channels for the material. • Activation energies show higher values for ordered sample due to confinement effect. • Role of electron-phonon interaction in the carrier thermalization process discussed. [ABSTRACT FROM AUTHOR]

In this work, we report the results of the compositional analysis of an aluminum gallium arsenide (AlGaAs) sample using the calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique. The AlGaAs sample was doped with three various concentrations of gallium (Ga), arsenic (As), and aluminum (Al), as reported by the manufacturer, and the CF-LIBS technique was employed to identify the doping concentration. A pulsed Q-switched Nd: YAG laser capable of delivering 200 and 400 mJ energy at 532 and 1064 nm, respectively, was focused on the target sample for ablation, and the resulting emission spectra were captured using a LIBS 2000+ spectrometer covering the spectral range from 200 to 720 nm. The emission spectra of the AlGaAs sample yielded spectral lines of Ga, As, and Al. These lines were further used to calculate the plasma parameters, including electron temperature and electron number density. The Boltzmann plot method was used to calculate the electron temperature, and the average electron temperature was found to be 5744 ± 500 K. Furthermore, the electron number density was calculated from the Stark-broadened line profile method, and the average number density was calculated to be 6.5 × 1017 cm−3. It is further observed that the plasma parameters including electron temperature and electron number density have an increasing trend with laser irradiance and a decreasing trend along the plume length up to 2 mm. Finally, the elemental concentrations in terms of weight percentage using the CF-LIBS method were calculated to be Ga: 94%, Al: 4.77% and As: 1.23% for sample-1; Ga: 95.63%, Al: 1.15% and As: 3.22% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The certified concentrations were Ga: 95%, Al: 3% and As: 2% for sample-1; Ga: 96.05%, Al: 1% and As: 2.95% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The concentrations measured by CF-LIBS showed good agreement with the certified values reported by the manufacturer. These findings suggest that the CF-LIBS technique opens up an avenue for the industrial application of LIBS, where quantitative/qualitative analysis of the material is highly desirable.

Las películas de AlGaAs fueron depositadas por pulverización catódica asistida por campo magnético sobre sustratos de vidrio y Si (100). Se mantuvo constante la temperatura del substrato y se varió la relación de la potencia de los blancos de Al y GaAs. Para disminuir los efectos del desacople del parámetro de red entre la capa de AlGaAs y los substratos, se depositó una capa buffer de GaAs. Los espectros de difracción de rayos X muestran que las películas son policristalinas con orientación preferencial (111). Los espectros Raman evidencian un comportamiento de dos modos, correspondiente a modos vibracionales TO y LO de GaAs y de AlAs, respectivamente.

The temperature dependences of the capacitance-voltage (C–V) characteristics and deep-level spectra of a graded high-voltage AlxGa1 –xAs p0–i–n0 junction grown by liquid-phase epitaxy via autodoping with background impurities are studied. Changes in the C–V characteristics at varied measurement temperature and optical illumination demonstrate that the p0-, i-, and n0-type layers in AlxGa1 –xAs under study contain bistable DX centers. Spectra furnished by deep-level transient spectroscopy (DLTS), measured at various bias voltages Vr and filling-pulse voltages Vf, show a positive DLTS peak for the n0-type layer, with a thermal activation energy of Et = 280 meV and electron-capture cross section of σn = 3.17 × 10–14 cm2, which is unusual for a majority-charge-carrier trap. This peak is attributed to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy U. [ABSTRACT FROM AUTHOR]

We report on AlGaAs‐based heterojunction solar cells grown by solid source molecular beam epitaxy (MBE). We investigate InGaP and AlGaAs material quality and we demonstrate significant efficiency improvements by combining the best of each alloy: a thick p‐AlGaAs base with tunable bandgap, and a thin 50 nm n‐InGaP emitter separated by a thin intrinsic AlGaAs layer. We report a certified solar cell conversion efficiency of 18.7% with a 2‐μm‐thick AlGaAs layer and a bandgap of 1.73 eV, suitable for high efficiency Si‐based tandem devices. [ABSTRACT FROM AUTHOR]

In this study, numerical optimization and analysis utilizing AMPS-1D software package of a simple model for tunnel junction (AlGaAs) between the top cell (AlGaAs) and bottom cell (SiGe) of cascade solar cells. The electrical properties and the photovoltaic performance parameters of AlGaAs/SiGe multijunction solar cells. The possible effects of base of the top cell layer thickness and doping level on solar cell performance parameters are addressed. The conversion efficiency of the solar cell has been found to increase significantly with the doping concentration in the range from 1015 to 1017 cm-3 of 19.52% to 31.19% under the AM1.5G spectrum and one sun. These results are very promising for future potential applications in multijunction and high performance AlGaAs/SiGe solar cells technology. [ABSTRACT FROM AUTHOR]

A method is proposed to control the distribution of carrier concentration over the profile of multilayer heteroepitaxial structures (HESs) with quantum-size active region based on the AlGaAs/GaAs heteropair grown with the aid of molecular beam epitaxy using electrochemical capacitance–voltage profiling (ECV). A calculation model for the region of the space charge at the electrolyte–semiconductor interface is developed. The ECV profiles of the HES grown on the GaAs〈100〉 substrates are analyzed. The limiting depths of the space-charge regions are calculated for different concentrations of carriers in the layers under study. Limitations of the method to control the distribution of carrier concentration in the quantum-size region of the HES are outlined. [ABSTRACT FROM AUTHOR]

An optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) with 3.25-W output power emitting around 750 nm is demonstrated. The gain structure incorporates AlGaAs quantum wells (QWs) and barriers, and AlGaInP claddings. The emission wavelength could be tuned from 740 to 770 nm. The development addresses the need for high brightness lasers at a wavelength range that has proven difficult to reach. The demonstrated structure exhibits polarization-related peculiarities, which cause polarization switching under increased pump power due to mode competition. The presence of birefringence inside the active region is attributed to known long-range ordering within the AlGaInP claddings which causes distorted beam profiles. This influence on laser features has not been reported in VECSELs so far. [ABSTRACT FROM AUTHOR]

The effects of surface passivation on AlGaAs/InGaAs/GaAs HEMTs using silicon nitride are presented. The passivated HEMT exhibited stable operation at elevated temperatures up to 480 K with excellent pinch-off characteristics. Furthermore, the interesting and anomalous dependence of the two-terminal gate–drain breakdown voltage on temperature is investigated. The high-speed performance of the SiN X -passivated HEMT with an f T = 20.1 GHz and an f max = 28.5 GHz is confirmed. The experimental results also demonstrate that the addition of a SiN X passivation layer to the AlGaAs/InGaAs/GaAs HEMTs increases the three-terminal on-state and off-state breakdown voltages and increases the cutoff frequency. Unlabelled Image • In this study, the interesting and anomalous dependence of the two-terminal gate–drain breakdown voltage on temperature is discussed. • Our experimental results demonstrate the improvements in the maximum extrinsic transconductance, breakdown characteristics, and cutoff frequency are observed after passivation with SiN X. • The double delta doping layers are used in our proposed HEMTs. [ABSTRACT FROM AUTHOR]

• Highly doped emitting window was fabricated by ZnO film and its thermal treatment. • Higher doping level of emission window limited increased effectively real emission region limited by current window. • Output power of 860 nm VCSEL was greatly enhanced by using highly Zn doped emitting window with optimized thermal condition. A highly doped emitting window for a vertical-cavity surface-emitting laser (VCSEL) was fabricated and its effect on the output power at a wavelength of 860-nm was investigated. The highly doped emitting window, which limited in required specific area, could be obtained by using various thermal conditions for patterned zinc oxide (ZnO). Experimental measurements showed that the highest doping concentration of 1.02 × 1019/cm3 was observed from patterned ZnO treated at 600 °C. The highly doped emitting window obtained by Zn diffusion effectively improved the real emission region confined by the current window owing to increase in the central concentration of the current injected from the top electrode. Among the developed VCSEL chips, the highest output power of 110 mW was observed with the use of a Zn-doped emitting widow at 600 °C, indicating an increase 47% compared with the output power of conventional chips (75 mW). For temperatures other than 600 °C, a relatively lower output power was obtained. The results show that the use of an emitting window highly doped with Zn can improve the output power of the VCSEL at a wavelength of 860-nm. It was verified that there exists an optimal thermal condition for the zinc diffusion process for patterned ZnO film required. [ABSTRACT FROM AUTHOR]

Improving the photovoltaic conversion efficiency requires a good choice for the structure of the cell. The front surfaces of the thin-film cell could improve these performances. In our work we have studied thin-film GaAs cells with thin ternary InGaP and AlGaAs layers used as a window. The one dimensional program SCAPS 1D has been used to study and optimize the performance of the GaAs cells in particular the window layer effect (the thickness and doping) and to compare between the two cells with In0.5Ga0.5P and Al0.2Ga0.8As window layers. The results have shown that the In0.5Ga0.5P layer window epitaxially grown on GaAs solar cell have the best performance compared with the Al0.2Ga0.8As layer window. The optimum thickness of the window is 0.1µm, and the maximum efficiency is about 25.02%. [ABSTRACT FROM AUTHOR]

Highlights • Finding of gain characteristics of type-I n-AlGaAs/GaAsP/p-AlGaAs nano-scale heterostructure. • Optimizing the tunability of TE and TM optical gain under high pressures along [001] and [100] directions. • Proving the usefulness of [001] pressure direction for significant improvement in optical gain characteristics. Abstract This paper gives a detailed report on the tunability of optical gain characteristics of type-I n-Al 0.45 Ga 0.55 As/GaAs 0.84 P 0.16 /p-Al 0.45 Ga 0.55 As nano-scale hetrostructure under the external pressures applied along [001] and [100] directions. In order to find the carriers wavefunctions, their localizations and sub-band dispersions in the heterostrcuture, a 6 × 6 K –L Hamiltonian was solved. In addition, the optical and momentum matrix elements were also calculated followed by the calculation of TE and TM optical gain under the applied pressure along [001] and [100] directions. According to the quantitative analysis of the simulated results, it can be suggested that the application of external pressure along [001] direction within TE mode is one of the preferable approaches for the efficient improvement in the gain characteristics of the n-Al 0.45 Ga 0.55 As/GaAs 0.84 P 0.16 /p-Al 0.45 Ga 0.55 As nano-scale hetrostructure based laser performance in the NIR (near ifrared region). [ABSTRACT FROM AUTHOR]

A technique for the examination of the photoluminescence spectra of multilayer heteroepitaxial structures with AlGaAs/GaAs quantum wells grown from molecular-beam epitaxy was developed. The size-quantization levels in quantum wells were calculated. Heat maps of distributions of peak wavelengths and intensities of photoluminescence spectra over the surface of epitaxial layers of different compositions were plotted. This mapping provided an opportunity to estimate the uniformity of distributions of the composition and thickness of epitaxial layers over the surface of samples. The results suggest possible ways to improve the techniques for acceptance and interoperational inspection of multilayer heteroepitaxial structures used in infrared photodetector arrays. [ABSTRACT FROM AUTHOR]

Highlights • Highly conductive GaP layer improved 860 nm GaAs based vertical cavity surface emitting laser (VCSEL). • Optimal thickness of GaP layer is effective in obtaining maximum emission area of GaAs based VCSEL. • Output power of 860 nm VCSEL was greatly enhanced by using GaP layer with optimized thickness. Abstract The use of a GaP barrier in a vertical-cavity surface-emitting laser (VCSEL) and its effect on output power at 860 nm were investigated. The GaP barrier was found to have higher conductivity from current–voltage measurements. This material is suitable for its use as a current spreading layer in the VCSEL based on (Al)GaAs. Experimental measurements show that the output power from the VCSEL effectively increased as the thickness of the GaP barrier increased, eventually saturating for a specific thickness value. The calculated real emission area and optical properties show that the current spreading effect in the GaP barrier is limited by the current window. Among different VCSEL chips, the highest output power of 26.5 mW was obtained using an optimal 3-µm-thick GaP barrier, which is an increase of 43% compared with the power output from the conventional structure. Nearly equal output powers were observed for structures with 3- and 6-μm GaP barriers. The results show that the GaP barrier used as the current spreading layer is essential for improving the output power from the VCSEL at 860 nm. The optimal thickness of the GaP barrier in the VCSEL strongly depends on the aperture diameter (real emission area), which can be determined from the current window. [ABSTRACT FROM AUTHOR]

Due to adjustable modal birefringence, suspended AlGaAs optical waveguides with submicron transverse sections can support phase-matched frequency mixing in the whole material transparency range, even close to the material bandgap, by tuning the width-to-height ratio. Furthermore, their single-pass conversion efficiency is potentially huge, thanks to the extreme confinement of the interacting modes in the highly nonlinear and high-refractive-index core, with scattering losses lower than in selectively oxidized or quasi-phase-matched AlGaAs waveguides. Here we compare the performances of two types of suspended waveguides made of this material, designed for second-harmonic generation (SHG) in the telecom range: (a) a nanowire suspended in air by lateral tethers and (b) an ultrathin nanorib, made of a strip lying on a suspended membrane of the same material. Both devices have been fabricated from a 123 nm thick AlGaAs epitaxial layer and tested in terms of SHG efficiency, injection and propagation losses. Our results point out that the nanorib waveguide, which benefits from a far better mechanical robustness, performs comparably to the fully suspended nanowire and is well-suited for liquid sensing applications.