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In this paper, we developed a theoretical model for the photothermal deflection technique in order to investigate the electronic parameters of three-layer semiconductor structures. This model is based on the resolution of thermal and photogenerated carrier diffusion-wave equations in different media. Theoretical results show that the amplitude and phase of the photothermal deflection signal is very sensitive to the nonradiative recombination parameters. The theoretical model is applied to one layer of InAs quantum dots (QDs) inserted in GaAs matrix InAs/GaAs QDs in order to investigate the QD density effects on nonradiative recombination parameters in InAs through fitting the theoretical photothermal beam deflection signal to the experimental data. It was found that the minority carrier lifetime and the electronic diffusivity decrease as functions of increasing InAs QD density. This result is also related to the decrease in the mobility from 21.58 to 4.17 (±12.9%) cm2/V s and the minority carrier diffusion length from 0.62 (±5.8%) to 0.14 (±10%) μm, respectively. Furthermore, both interface recombination velocities S 2 / 3 of GaAs/InAs (QDs) and S 1 / 2 of InAs (QDs)/GaAs increase from 477.7 (±6.2%) to 806.5 (±4%) cm/s and from 75 (±7.8%) to 148.1 (±5.5%) cm/s, respectively. [ABSTRACT FROM AUTHOR]

Scanning spreading resistance microscopy (SSRM) measurements were performed on GaAs thick films grown by hydride vapor phase epitaxy technology under different growth conditions to evaluate their carrier concentrations. For this purpose, a calibration curve was established based on a multilayer staircase structure grown by molecular beam epitaxy. The dopant calibration range measured by secondary ion mass spectrometry is from 5 × 1016 to 1019 cm−3. An abnormal phenomenon in the calibration process was explained by taking into account the parasitic parallel resistance of the calibration samples. Finally, the calibration curve was used to quantitatively analyze the carriers inside the Zn doping p-type GaAs film from 4 × 1016 to 1018 cm−3 range. We demonstrate here the applicability of SSRM to the in-depth analysis of thick epilayers, providing new inputs for the control of thick film technologies. [ABSTRACT FROM AUTHOR]

Strain engineering using ion beams is a current topic of research interest in semiconductor materials. Synchrotron-based high-resolution x-ray diffraction has been utilized for strain-depth analysis in GaAs irradiated with 300 keV Ar and 4H-SiC and GaAs irradiated with 100 MeV Ag ions. The direct displacement-related defect formation, anticipated from the elastic energy loss of Ar ions, can well explain the irradiation-induced strain depth profiles. The maximum strain in GaAs is evaluated to be 0.88% after Ar irradiation. The unique energy loss depth profile of 100 MeV Ag (swift heavy ions; SHIs) and resistance of pristine 4H-SiC and GaAs to form amorphous/highly disordered ion tracks by ionization energy loss of monatomic ions allow us to examine strain buildup due to the concentrated displacement damage by the elastic energy loss near the end of ion range (∼ 12 μ m). Interestingly, for the case of SHIs, the strain-depth evolution requires consideration of recovery by ionization energy loss component in addition to the elastic displacement damage. For GaAs, strain builds up throughout the ion range, and the maximum strain increases and then saturates at 0.37% above an ion fluence of 3 × 10 13 Ag/cm 2. For 4H-SiC, the maximum strain reaches 4.6% and then starts to recover for fluences above 1 × 10 13 Ag/cm 2. Finally, the contribution of irradiation defects and the purely mechanical contribution to the total strain have been considered to understand the response of different compounds to ion irradiation. [ABSTRACT FROM AUTHOR]

Noting that the conventional collision-dominated electron transport perspective is only relevant when the length scale over which the transit occurs is greater than the electron's mean free path, one can conceptually partition the electron transport "space" into collision-dominated and ballistic electron transport regimes. As the boundaries between these regimes are quite porous, in this analysis, we devise a means of quantitatively examining the transition between electron transport regimes as the length scale is reduced on a continuum basis. Our approach introduces a collision-dominated fractional scattering parameter, this parameter quantifying the fraction of the total scattering rate that arises purely from bulk scattering processes, contact scattering also contributing to the total scattering rate. We pursue this analysis for two conventional semiconductors of interest, silicon and gallium arsenide. A determination of the dependence of the results on both the length scale and the crystal temperature is pursued. Finally, for the specific case of room temperature, a comparison with the results of experiment is performed. [ABSTRACT FROM AUTHOR]

Machine learned potentials (MLPs) have been widely employed in molecular dynamics simulations to study thermal transport. However, the literature results indicate that MLPs generally underestimate the lattice thermal conductivity (LTC) of typical solids. Here, we quantitatively analyze this underestimation in the context of the neuroevolution potential (NEP), which is a representative MLP that balances efficiency and accuracy. Taking crystalline silicon, gallium arsenide, graphene, and lead telluride as examples, we reveal that the fitting errors in the machine-learned forces against the reference ones are responsible for the underestimated LTC as they constitute external perturbations to the interatomic forces. Since the force errors of a NEP model and the random forces in the Langevin thermostat both follow a Gaussian distribution, we propose an approach to correcting the LTC by intentionally introducing different levels of force noises via the Langevin thermostat and then extrapolating to the limit of zero force error. Excellent agreement with experiments is obtained by using this correction for all the prototypical materials over a wide range of temperatures. Based on spectral analyses, we find that the LTC underestimation mainly arises from increased phonon scatterings in the low-frequency region caused by the random force errors. [ABSTRACT FROM AUTHOR]

The Sn-doping effects on the electrical conduction and optical properties of GaAs(631)A epilayers grown by molecular beam epitaxy were investigated. We found that the conduction type conversion, frequently observed in the doping of layers grown on high-index substrates, is avoided when tin-doping is implemented. The maximum free-carrier concentration (n) obtained in GaAs(631):Sn was 2 × 1019 cm−3, an order of magnitude higher than previously reported for GaAs(631):Si, and within the same order of magnitude for the growth of GaAs(100):Si. The electron mobility was suitable for many optoelectronic applications. Raman spectroscopy showed low lattice disorder in (631) oriented samples, compared with singular (100) samples. The photoluminescence characterization of the samples revealed the blueshift of the optical transitions close to E0 associated with the Moss–Burstein effect for Sn doping. Photoreflectance spectroscopy was used to study the doping properties at the critical points E1 and E1 + Δ1, where the major affectation with n was perceived in the broadening parameter Γ. [ABSTRACT FROM AUTHOR]

A wire-on-well (WoW) structure was fabricated using InGaAs/GaAs/GaAsP superlattice device growth technology. This structure modifies the local concentration of carriers in the quantum well and lengthens the carrier lifetime to increase carrier transport efficiency. However, the reason for this remains unclear. Therefore, we investigated the detailed carrier transition properties using photoluminescence (PL) and photoreflectance measurements. Regarding the PL spectra at 4 K, two characteristic peaks at 1.39 and 1.34 eV were observed. Both transitions are attributed to the recombination between the first quantum level of the electron (e1) and that of the heavy hole (hh1). We also discussed the carrier distribution in the WoW structure and found that the maximum carrier existing probabilities for e1 and hh1 are located at different positions. The less overlapping of the wavefunctions causes low transition probability and results in the observed long carrier lifetime. An additional prominent result in the WoW structure is the blue shift attributed to the 1.34 eV PL peak induced by increasing laser excitation power. We found that the blue shift occurred by the screening of the electric field caused by the compressive strain, as in the case of the quantum-confined Stark effect. [ABSTRACT FROM AUTHOR]

We demonstrated the crystal growth of group-III arsenides (III-As) on GaN via an arsenidation layer and GaN-channel electron mobility transistors (HEMTs) with a regrowth InAs/GaAs source and drain (S/D) region. By annealing under an AsH3 atmosphere, the surface of a GaN (0001) template is arsenided. We grew ⟨ 111 ⟩ oriented InAs and GaAs on arsenided GaN. Silicon-doped n-type InAs with a carrier mobility of over 1500 cm2/V s and a carrier concentration of over 1 × 1019 cm−3 was successfully obtained. The fabrication process and direct-current characteristics of GaN-channel HEMTs with the regrown Si-doped InAs/GaAs S/D region were demonstrated for the first time. A maximum transconductance estimated from transfer characteristics was as high as ∼195 mS/mm for the HEMT with a gate length of 2 μm without passivation, which is comparable to those for the HEMT without any S/D regrowth. The impact of the InAs/GaAs S/D region on the on-resistance of the fabricated HEMTs was estimated to be ∼0.9 Ω mm, which can be reduced by optimizing the device structures and process conditions. These results indicate that the process of GaN arsenidation and III-As regrowth can be used without any device performance degradation. Therefore, further lowering the ohmic contact resistivity and on-resistance of GaN-channel HEMTs is possible by maturing the manufacturing-process technology of III-As-contained GaN-channel HEMTs. [ABSTRACT FROM AUTHOR]

A band design of a quantum cascade laser with a generation frequency higher than 6 THz and an active region based on four GaAs/Al0.14Ga0.86As quantum wells is proposed. Calculations were carried out based on the solution of the Schrödinger equation taking into account the dephasing of quantum states, as well as a closed system of balance equations. The temperature dependences of the gain at frequencies of 6.3–6.6 THz were calculated for the proposed quantum cascade laser with a double metal waveguide. Features of the proposed laser structure include two injection quantum wells and the suppression of non-radiative transitions between laser levels. According to calculations, this provides the maximum operating temperature of up to 81 K at 6.4 THz. The results of this study open up the way for quantum cascade lasers based on GaAs/AlGaAs to operate at frequencies above 6 THz. [ABSTRACT FROM AUTHOR]

We present a systematic investigation of the optical losses in GaAs photonic crystal cavities with and without embedded self-assembled In(Ga)As quantum dots (QDs) to shed light on additional loss mechanisms related to the presence of the QDs. To clarify the role of the measurement method, we propose an experimental configuration where the optical properties can be evaluated simultaneously through reflection and photoluminescence measurements. Independently of the measurement method, we observe a reduced quality (Q) factor in cavities with embedded QDs when compared to the passive counterparts. Our analysis indicates that these additional losses—about 7 GHz—are unrelated to direct excitonic absorption for the investigated areal QD densities of 175 μ m − 2 . We analyze several mechanisms which could explain our observations and suggest that a possible origin could be unsaturable absorption from midgap defects introduced by the QD growth. [ABSTRACT FROM AUTHOR]

In this study, the degradation behavior of flexible GaInP/GaAs/InGaAs (IMM3J) solar cells and their metamorphic subcells under 1 MeV electron irradiation was investigated. The remaining factors such as short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power (Pmax) were 95.62, 85.52, and 79.73%, respectively, at an irradiation fluence of 2 × 1015 e/cm2. The spectral responses of the InGaAs and GaAs subcells degraded significantly, and the InGaAs subcell experienced greater degradation than the GaAs subcell after irradiation. In addition, the current-limiting unit was switched from GaInP to InGaAs after irradiation. Defect analysis by deep-level transient spectroscopy (DLTS) revealed that with increasing irradiation fluence, the defects that had the greatest impact on the performance of GaAs subcells were EV + 0.36 and EV + 0.42 eV. For InGaAs subcells, the defects that had the greatest impact on the performance were EV + 0.29 and EV + 0.24 eV. The decrease in the minority carrier lifetime is the main reason for the decrease in the electrical performance of solar cells, and the variation in the effective minority carrier lifetime (τeff) in the subcells with the irradiation fluence was calculated based on the DLTS results. At a fluence of 2 × 1015 e/cm2, the τeff of the GaAs and InGaAs subcells decreased from 2.93 × 10−10 and 9.10 × 10−10 s to 1.56 × 10−11 and 1.60 × 10−12 s, respectively. These results provide a reference for predicting the degradation of short-circuit current and open-circuit voltage of flexible IMM3J. [ABSTRACT FROM AUTHOR]

The effect of the GaAsP strain-compensating layer on type-II GaAs1−xSbx/InyGa1−yAs was investigated. GaAsSb/InGaAs multiple quantum wells (MQWs) without and with GaAsP strain-compensating layers were grown by molecular beam epitaxy. Increasing Sb or In compositions can extend photoluminescence (PL) emission at longer wavelength along with the highly induced compressive strain in the QWs. The power-dependent PL measured at low temperature reveals the type-II band characteristics of the GaAs1−xSbx/InyGa1−yAs system. A detailed analysis of the experimental data reveals that the GaAsP layers compensate the compressive strain of GaAsSb/InGaAs. The type-II QWs with GaAsP layers, (8 nm) GaAs0.84Sb0.16/(2.5 nm) In0.3Ga0.7As/(10 nm) GaAs0.85P0.15, emits PL at ∼1.1 μm, up to 210 K, while the PL of those strained sample without GaAsP vanishes at lower temperature. In view of the described sample, x-ray diffraction (XRD) analysis along with the simulation shows the validity of the procedure, resulting in nearly matched parameters of QW thicknesses and material compositions—(8.9 nm) GaAs0.835Sb0.165/(2.3 nm) In0.3Ga0.7As/(10.3 nm) GaAs0.85P0.15, with those of the designed QW. The thicknesses of QW from the TEM image, (8.6 nm) GaAsSb/(3.1 nm) InGaAs/(10.1 nm) GaAsP, agree well with the XRD results. [ABSTRACT FROM AUTHOR]

GaAs surfaces require electrical and chemical passivation for semiconductor devices, but in order to have air stable passivation, high temperatures have been previously required in the passivation step. Here, we demonstrate air-stable, ex situ plasma passivation of GaAs using consecutive hydrogen and nitrogen plasmas at room temperature. No pre-clean using deoxidizing wet chemistry or other means is required. The hydrogen plasma step removes surface oxides and As, which leaves a Ga-rich layer that the nitrogen plasma then turns to GaN. The formed GaN layer efficiently passivates the surface. The plasma-passivated GaAs shows upto 5 × room-temperature photoluminescence after 1 year, and room-temperature time-resolved photoluminescence demonstrates robust passivation even after 3 years, both comparisons to similarly aged unpassivated GaAs. Atomic force microscopy was used to confirm that the passivated surfaces can be made smooth enough for microelectronic applications. Grazing incidence x-ray diffraction indicated that the nitride films are amorphous, and energy-dispersive x-ray spectroscopy was used to estimate the nitrogen content. We used a common inductively coupled plasma reactive ion etching system for plasma passivation, thus enabling the rapid adoption of this technique. [ABSTRACT FROM AUTHOR]

Design strategies for improving terahertz (THz) quantum cascade lasers (QCLs) in the 5-6 THz range are investigated numerically and experimentally, with the goal of overcoming the degradation in performance that occurs as the laser frequency approaches the Reststrahlen band. Two designs aimed at 5.4 THz were selected: one optimized for lower power dissipation and one optimized for better temperature performance. The active regions exhibited broadband gain, with the strongest modes lasing in the 5.3-5.6 THz range, but with other various modes observed ranging from 4.76 to 6.03 THz. Pulsed and continuous-wave (cw) operation is observed up to temperatures of 117 K and 68 K, respectively. In cw mode, the ridge laser has modes up to 5.71 THz - the highest reported frequency for a THz QCL in cw mode. The waveguide loss associated with the doped contact layers and metallization is identified as a critical limitation to performance above 5 THz.

A study of residual mechanical stresses in the surface layer of the HgCdTe/CdTe/ZnTe/GaAs structure based on the registration of the second harmonic signal characteristics of reflected IR laser radiation from the surface of the studied sample passed through a nonlinear crystal was carried out. It is shown that such a sensitive method makes it possible to obtain information about the anisotropy of the polarization of the reflected radiation, caused by the residual deformation. Observations of the fine structure of the angular sweep of the second harmonic signal suggest a complex structure of residual stresses related to the presence of misoriented areas. The results were compared with data obtained from measurements of the azimuthal dependence of the self-reflected second harmonic signal from the sample surface. [ABSTRACT FROM AUTHOR]

N-type doping in GaAs is a self-limited process, rarely exceeding a carrier concentration level of 1019 cm−3. Here, we investigated the effect of intense pulsed light melting on defect distribution and activation efficiency in chalcogenide-implanted GaAs by means of positron annihilation spectroscopy and electrochemical capacitance–voltage techniques. In chalcogenide-doped GaAs, donor–vacancy clusters are mainly responsible for donor deactivation. Using positrons as a probe of atomic scale open volumes and DFT calculations, we have shown that after nanosecond pulsed light melting the main defects in heavily doped GaAs are gallium vacancies decorated with chalcogenide atoms substituting As, like VGa–nTeAs or VGa–nSAs. The distribution of defects and carriers in annealed GaAs follows the depth distribution of implanted elements before annealing and depends on the change in the solidification velocity during recrystallization. [ABSTRACT FROM AUTHOR]

Terahertz (THz) radiation sources based on two‐color femtosecond plasmas in air are becoming a mature technology for coherent spectroscopy and strong‐field physics across the extended THz range to several tens of THz. The field‐resolved detection of such THz transients relies on the third‐order nonlinearity of the detection medium. Here, a comparative measurement is demonstrated with air‐biased coherent detection (ABCD) and solid‐state biased detection (SSBCD) as a novel method to measure the dispersion of the magnitude and phase of the relevant third‐order nonlinearity χ(3)(2ω±Ω;ω,ω,±Ω)$\chi ^{(3)}(2\omega \pm \Omega;\omega,\omega,\pm \Omega)$ for fused silica (SiO2${\rm SiO}_2$) and silicon nitride (SiN). Based on the development of the ultrabroadband SSBCD device with a detection bandwidth exceeding 30 THz, χ(3)$\chi ^{(3)}$ measurements are obtained across the 1–28 THz frequency range, hence covering the THz and far‐infrared. It is shown that the vibrational modes in SiO2${\rm SiO}_2$ and SiN in the THz range lead to strong resonant enhancement and dispersion of the nonlinearity. The SSBCD devices operate down to nanojoule (nJ) probe energy, and their is demonstrated by measuring the dielectric function of the Lorentzian line profile of transverse‐optical (TO) phonon mode at 9 THz in single‐crystal gallium arsenide (GaAs) and observing the weak phonon combination bands near the TO phonon. [ABSTRACT FROM AUTHOR]

This research provides a flexible approach to manipulate formation of InGaAs nanostructures on the GaAs (100) surface by varying arsenic (As4) beam equivalent pressure (BEP). By selecting the As4/(In+Ga) BEP ratio to be 4, 8, 20, 50 and 100, we were able to obtain different quantum structures from quantum well (QW) to quantum dots (QDs), then to spatially ordered quantum dot chains (QD-chains), and finally to quantum wires (QWRs), respectively. This transformation of nanostructures was explained by anisotropic surface diffusion coupled with the strain relieving Stranski–Krastanov growth mode, while the anisotropy was modulated by increasing As4 flux and subsequently enhanced by multilayer-stacking growth with a suitable spacer thickness. Photoluminescence characteristics show correlation to the nanostructure morphology for each sample. In particular, the formation of QD-chains and QWRs results in anisotropic features that offer potential device applications. [ABSTRACT FROM AUTHOR]

In this paper, small-signal model parameters and RF characteristics of the GaN-based Dual-Metal Cylindrical Surrounding Gate-Junctionless Accumulation Mode (DM-CSG-JAM) MOSFET has been extracted. Better scattering parameters has been observed for GaN-based DM-CSG-JAM MOSFET over other analogous structures which confirms its applications for RF domain. Also, enhanced drain current, transconductance, cut-off frequency, Ion/Ioff ratio, etc. have been observed for the GaN-based device. The performance of the GaN-based MOSFET has also been compared with the other compound semiconductors (GaAs, InP) and silicon-based DM-CSG-JAM MOSFET. On account of the eminent properties possessed by GaN, the GaN-based device shows outstanding characteristics over the other semiconductor-based device. [ABSTRACT FROM AUTHOR]

A fully integrated gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) power amplifier (PA) for wireless local area network 802.11ax applications is presented in this paper. The structure consists of two‐stage power cells. To satisfy the high linearity requirements of IEEE 802.11ax, we analyzed the distortion of amplitude‐to‐amplitude and amplitude‐to‐phase. Due to the thermal and voltage sensitivity of GaAs HBT, an adaptive bias circuit is designed to ensure linearity. Moreover, an efficient passive output matching network is designed by analyzing the efficiency of the passive network. The design electromagnetic structure is fabricated in a 2‐μm GaAs HBT process. Under continuous wave testing, the output power reaches 27.2 dBm and the maximum efficiency of 28% at 2.4 GHz. Under the excitation of a 40 MHz 1024‐quadratic amplitude modulation signal, the output power meeting error vector magnitude of −35 dB reaches 16.8–17.2 dBm from 2.4 to 2.5 GHz. [ABSTRACT FROM AUTHOR]

The Q resolution in Bonse–Hart double‐crystal diffractometers is determined for a given Bragg angle by the value of the crystallographic structure factor. To date, the reflections Si 220 or Si 111 have been used exclusively in neutron scattering, which provide resolutions for triple‐bounce crystals of about 2 × 10−5 Å−1 (FWHM). The Darwin width of the GaAs 200 reflection is about a factor of 10 smaller, offering the possibility of a Q resolution of 2 × 10−6 Å−1 provided crystals of sufficient quality are available. This article reports a feasibility study with single‐bounce GaAs 200, yielding a Q resolution of 4.6 × 10−6 Å−1, six times superior in comparison with a Si 220 setup. [ABSTRACT FROM AUTHOR]

It is demonstrated that single‐crystalline and highly doped GaAs membranes are excellent candidates for realizing infrared‐transparent shields of electromagnetic interference at millimeter frequencies. Measured optical transmittance spectra for the semiconductor membranes show resonant features between 750 and 2500 nm, with a 100% maximum transmittance. The shielding effectiveness of the membranes is extracted from measured scattering parameters between 65 and 85 GHz. Selected GaAs membranes and membranes/polyamide films exhibit shielding effectiveness ranging from 22 to 40 dB, which are suitable values to ensure the safe operation of infrared devices for commercial applications. Theoretical calculations based on a plane wave model show that the interplay of primary reflection and multiple internal reflections of the radio‐frequency waves results in broadband shielding capabilities of the membrane between 10 and 300 GHz. [ABSTRACT FROM AUTHOR]

This paper reports on a monolithically integrated gallium arsenide (GaAs)-based photonic integrated circuit platform for wavelengths around 1064 nm. Enabled by spatially selective quantum well removal and two-step epitaxial growth, it supports on-chip gain as well as passive waveguides. In addition, shallow- and deep-etched waveguides are realized. The former result in waveguide losses of less than 2 dB/cm, while the latter enable compact integrated waveguide components. To demonstrate the performance of the platform, racetrack ring resonators based on deep-etched Euler bends and shallow-etched directional couplers are realized, achieving high intrinsic quality factors of 2.6 × 105 and 3.2 × 105 for the fundamental TE and TM mode, respectively. To demonstrate the use of these resonators, ring-resonator-coupled lasers are fabricated, resulting in one-sided output powers of up to 14 mW and single-mode operation with 40 dB side-mode suppression. The successful integration of ring resonators on a GaAs-based active/passive photonic integrated circuit platform paves the way for the realization of fully monolithic, widely tunable, and narrow linewidth ring-resonator-coupled laser sources. [ABSTRACT FROM AUTHOR]

Semiconductor photodetectors can work only in specific material-dependent light wavelength ranges, connected with the bandgaps and absorption capabilities of the utilized semiconductors. This limitation has driven the development of hybrid devices that exceed the capabilities of individual materials. In this study, for the first time, a hybrid heterojunction photodetector based on methylammonium lead bromide (MAPbBr3) polycrystalline film deposited on gallium arsenide (GaAs) was presented, along with comprehensive morphological, structural, optical, and photoelectrical investigations. The MAPbBr3/GaAs heterojunction photodetector exhibited wide spectral responsivity, from 540 to 900 nm. The fabrication steps of the prototype device, including a new preparation recipe for the MAPbBr3 solution and spinning, will be disclosed and discussed. It will be shown that extending the soaking time and refining the precursor solution's stoichiometry may enhance surface coverage, adhesion to the GaAs, and film uniformity, as well as provide a new way to integrate MAPbBr3 on GaAs. Compared to the pristine MAPbBr3, the enhanced structural purity of the perovskite on GaAs was confirmed by X-ray Diffraction (XRD) upon optimization compared to the conventional glass substrate. Scanning Electron Microscopy (SEM) revealed the formation of microcube-like structures on the top of an otherwise continuous MAPbBr3 polycrystalline film, with increased grain size and reduced grain boundary effects pointed by Energy-Dispersive Spectroscopy (EDS) and cathodoluminescence (CL). Enhanced absorption was demonstrated in the visible range and broadened photoluminescence (PL) emission at room temperature, with traces of reduction in the orthorhombic tilting revealed by temperature-dependent PL. A reduced average carrier lifetime was reduced to 13.8 ns, revealed by time-resolved PL (TRPL). The dark current was typically around 8.8 × 10−8 A. Broad photoresponsivity between 540 and 875 nm reached a maximum of 3 mA/W and 16 mA/W, corresponding to a detectivity of 6 × 1010 and 1 × 1011 Jones at −1 V and 50 V, respectively. In case of on/off measurements, the rise and fall times were 0.40 s and 0.61 s or 0.62 s and 0.89 s for illumination, with 500 nm or 875 nm photons, respectively. A long-term stability test at room temperature in air confirmed the optical and structural stability of the proposed hybrid structure. This work provides insights into the physical mechanisms of new hybrid junctions for high-performance photodetectors. [ABSTRACT FROM AUTHOR]

We present an efficient machine learning based automated framework for the fast tuning of single-electron pump devices into current quantization regimes. It uses a sparse measurement approach based on an iterative active learning algorithm to take targeted measurements in the gate voltage parameter space. When compared to conventional parameter scans, our automated framework allows us to decrease the number of measurement points by about an order of magnitude. This corresponds to an eightfold decrease in the time required to determine quantization errors, which are estimated via an exponential extrapolation of the first current plateau embedded into the algorithm. We show the robustness of the framework by characterizing 28 individual devices arranged in a GaAs/AlGaAs multiplexer array, which we use to identify a subset of devices suitable for parallel operation at communal gate voltages. The method opens up the possibility to efficiently scale the characterization of such multiplexed devices to a large number of pumps. [ABSTRACT FROM AUTHOR]

It is found out that the HR-GaAs:Cr material is formed when the conductivity of n-GaAs is compensated by NCr chromium atoms, resulting in highly localized acceptor states at the mid of the bandgap. Such a structure is characterized by both the extremely high resistivity (ρmax), exceeding the resistance (ρi) of its own semiconductor (ρmax ≥ ρi), and the prolonged lifetime (τn) of non-equilibrium electrons, determining its high photosensitivity. Thus, it can be implemented in various basic electronic components for functional devices. [ABSTRACT FROM AUTHOR]

The study provides experimental validation for the correlation between the photoreflectance signal's time constant and the capacitances of various p - n junction quantum-dot solar cells. Photoreflectance spectra were measured on four structures with varying InAs/GaAs quantum dot layer thicknesses (1.7–3 monolayers), and time constants were extracted from the phase diagrams. A linear relationship was observed between these time constants and the cells' capacitances. Analysis of the phase diagrams for different chopping frequencies revealed that this approach allows for the assessment of capacitances of a sample set through a single photoreflectance measurement. These findings underscore the potential of photoreflectance as a straightforward, contactless technique for comparing junction capacitance across samples. Furthermore, this work could enhance our understanding of photoreflectance in solar cell characterization and present a practical tool for evaluating capacitance in various optoelectronic devices, broadening the utility of nondestructive characterization techniques. [ABSTRACT FROM AUTHOR]

Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment. [ABSTRACT FROM AUTHOR]

This review paper examines the advancements in solid-state power amplifiers (SSPAs) for wireless communication technology. As mobile devices rely on efficient power amplifiers to maintain battery life and ensure clear signal transmission, fabrication technologies like complementary metal–oxide–semiconductor (CMOS) and gallium nitride (GaN) are revolutionizing power amplifier (PA) design. The choice of material depends on the working frequency, with gallium arsenide (GaAs) and GaN suitable for frequencies under 100 GHz, and indium phosphide reaching up to 500 GHz. However, cost is a crucial factor in industrial manufacturing, making CMOS technology advantageous for on-chip system integration. Millimeter-wave chips have different requirements based on their application scenarios. In the Ka-band (26.5–40 GHz), high-power GaN and GaAs chips are preferred for satellite and long-distance communication. In contrast, the 60 GHz band is suited for short-distance high-speed communication and consumer electronics, making lower-cost CMOS and germanium silicon devices the preferred choice. This paper explores critical design considerations for SSPAs, focusing on common structures like envelope tracking, Doherty amplifiers, envelope elimination and restoration, and various linearization methods. We provide a clear comparison of their strengths and weaknesses to empower readers to select the optimal SSPA structure for their needs. Our review aims to facilitate informed decisions in the development of efficient and cost-effective SSPAs for advancing wireless communication technology. [ABSTRACT FROM AUTHOR]

Passivation capping that enhances the photoluminescence (PL) of molecular beam epitaxy (MBE)-grown InAs surface quantum dots (SQDs) is realized by ex situ low-temperature atomic layer deposition (ALD)-grown Al2O3. As the Al2O3 cap thickness increased from 2 to 30 nm, the PL intensity was enhanced by 2.7-fold and the blue shift was suppressed. This is in strong contrast to wet chemistry passivation and in situ GaAs capping by MBE, both of which resulted in significant PL blueshift, due to etching in the former, and In/Ga intermixing and strain in the latter. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the Al2O3 cap layer mimics the shape of the underlying SQDs. The cross-sectional transmission electron microscopy (TEM) further reveals that the SQD size and shape remained unchanged after Al2O3 capping, which is in strong contrast to MBE-capping. The passivation mechanisms and native oxide reduction by trimethylaluminum (TMA), including self-clean-up reaction through ligand exchange, are discussed based on the results by x-ray photoelectron spectroscopy (XPS). A detailed comparison between Al2O3 and ZnO cap layers reveals the significance of the cap properties on the SQD size/shape and PL blueshift. While the size/shape of SQDs is preserved by Al2O3 capping, the apex is slightly removed by ZnO capping, resulting in a stronger PL blueshift compared to Al2O3. [ABSTRACT FROM AUTHOR]

The ever-present demand for high-performance HgCdTe infrared detectors with larger array size and lower cost than currently available technologies based on lattice-matched CdZnTe (211)B substrates has fuelled research into heteroepitaxial growth of HgCdTe and CdTe buffer layers on lattice-mismatched alternative substrates with a (211)B orientation. Driven by the large lattice mismatch, the heteroepitaxial growth of (Hg)CdTe can result in (133)B-orientated material, which, however, has been less explored in comparison to (211)B-oriented growth. Herein, we report on the structural properties of heteroepitaxially grown single-crystal II–VI CdTe (133)B-oriented buffer layers on III–V GaAs (211)B substrates. Azimuthal-dependent x-ray double-crystal rocking curve measurements for the CdTe buffer layers show that the full-width at half-maximum value obtained along the GaAs [ 1 ¯ 11 ] direction is narrower than that obtained along the GaAs [ 01 1 ¯ ] direction, which is presumably related to the in-plane anisotropic structural characteristics of the grown CdTe layers. By incorporating strained CdZnTe/CdTe superlattice-based dislocation filtering layers (DFLs), a significant improvement in material quality has been achieved in (133)B-orientated CdTe buffer layers, including a reduced etch pit density in the low-105 cm−2 range and improved surface roughness. These results indicate that the CdTe (133)B DFL buffer layer process is a feasible approach for growing high-quality CdTe and HgCdTe materials on large-area, low-cost alternative substrates. [ABSTRACT FROM AUTHOR]

The strain field of the emitters of one unstressed and two electrically stressed oxide-confined GaAs-based vertical-cavity surface-emitting lasers has been analyzed. The components of the strain tensor in the optical aperture, in the quantum wells, and at the oxide edge of the lamellas have been measured by nano-beam precession electron diffraction and geometrical phase analysis. The measurements have been used to validate the simulations based on the finite element method (FEM) of the mechanical behavior of the emitters. The FEM model is used to quantify the strain caused by the lattice mismatch of the GaAs-based epitaxial layers and the volume variation of the Al 98 Ga 2 As layer due to selective oxidation. The first is calculated as a function of the misfit strain and corresponds very well to the measured values. The latter is calibrated assuming that the thickness of the oxide is expanded by 4 % in both the unstressed sample and the stressed sample with dislocations. Instead, it is contracted by 8 % for the sample where the stress test has caused further oxidation. [ABSTRACT FROM AUTHOR]

Carrier dynamics detection in different dimensions (space, time, and energy) with high resolutions plays a pivotal role in the development of modern semiconductor devices, especially in low‐dimensional, high‐speed, and ultrasensitive devices. Here, a femtosecond electron‐based versatile microscopy is reported that combines scanning ultrafast electron microscopy (SUEM) imaging and time‐resolved cathodoluminescence (TRCL) detection, which allows for visualizing and decoupling different dynamic processes of carriers involved in surface and bulk in semiconductors with unprecedented spatiotemporal and energetic resolutions. The achieved spatial resolution is better than 10 nm, and the temporal resolutions for SUEM imaging and TRCL detection are ≈500 fs and ≈4.5 ps, respectively, representing state‐of‐the‐art performance. To demonstrate its unique capability, the surface and bulk carrier dynamics involved in n‐type gallium arsenide (GaAs) are directly tracked and distinguished. It is revealed, in real time and space, that hot carrier cooling, defect trapping, and interband‐/defect‐assisted radiative recombination in the energy domain result in ordinal super‐diffusion, localization, and sub‐diffusion of carriers at the surface, elucidating the crucial role of surface states on carrier dynamics. The study not only gives a comprehensive physical picture of carrier dynamics in GaAs, but also provides a powerful platform for exploring complex carrier dynamics in semiconductors for promoting their device performance. [ABSTRACT FROM AUTHOR]

Nonreciprocity has become a research hotspot in the field of thermal radiation. Nonetheless, the majority of current nonreciprocal thermal radiation is confined to TM polarization. This paper introduces a two-dimensional nanograting structure exhibiting strong dual-polarization nonreciprocal thermal radiation. The grating is composed of a GaAs-based periodic nanoarray, a magneto-optic medium layer (InAs), and a metallic reflective layer (Al). The impact of nonreciprocity under different polarizations was investigated using rigorous coupled-wave analysis. Additionally, the magnetic field energy distribution was studied, and an explanation for the observed phenomenon of the device's nonreciprocal thermal radiation was given for both TE and TM polarizations. The present study is expected to contribute insights for the study of nonreciprocal thermal radiation. [ABSTRACT FROM AUTHOR]

The kinetics of the interaction of high-frequency plasma of difluorodichloromethane and its mixture with helium with the surface of gallium arsenide (GaAs) is experimentally studied. It is established that in the studied range of conditions, the original difluorodichloromethane molecule completely decomposed into atomic carbon. It is confirmed that the main chemically active particles responsible for etching are reactive chlorine atoms. It is shown that the etching process occurs in the mode of an ion-stimulated chemical reaction, where the desorption of products under the influence of ion bombardment plays a significant role in cleaning the surface. The emission spectra of plasma radiation in the presence of a GaAs semiconductor wafer are analyzed. The control lines and bands are selected to control the rate of the etching process based on the emission intensity of the lines and bands of the etching products. [ABSTRACT FROM AUTHOR]

This paper discusses the process of designing and manufacturing a wideband power amplifier operating in the S-band. To amplify a low power and broadband radio frequency signals from 2.1 GHz to 2.5 GHz, the proposed power amplifier uses a diagram of a two-stages amplification with peak offset amplification frequency 2.3 GHz. The power amplifier is designed with a center frequency difference of 2.2 GHz and 2.4 GHz respectively to achieve a bandwidth of 400 MHz. The proposed power amplifier (PA) uses RF transistor SHF-0589 using gallium arsenide heterostructure field-effect transistor (GaAs HFET) technology for high gain and low power consumption. The complete amplifier achieves power gain 21.1 dB inband 2.1-2.5 GHz and achieve maximum power gain of 22.5 dB at the frequency of 2.4 GHz; the output power rise up to 33 dBm; input reflection coefficient (S11) reaches -19.2 dB and output reflection coefficient reaches -17.2 dB. The designed amplifier circuit can be used for wireless sensor networks operating at S-band. [ABSTRACT FROM AUTHOR]

We demonstrated the linear, radial, and annular ripple formation on the surface of GaAs. The formation of linear ripples was optimized by the number of shots and the fluence of 30 ps, 532 nm pulses. The radial and annular nanoripples were produced under the ablation using doughnut-like beams possessing azimuthal and radial polarizations, respectively. We compare the ripples and grooves formed by a linearly polarized Gaussian beam relative to an annular vector beam. The joint overlap of sub-wavelength grooves with ripples formed by azimuthally and radially polarized beams was reported. The conditions under which the shape of radial and ring-like nano- or micro-relief on the GaAs surface can be modified by modulating the polarization of laser pulse were determined. The resultant surface processing of GaAs using a laser beam with different polarization modes is useful for exploring valuable insights and benefits in different applications. [ABSTRACT FROM AUTHOR]

The experimental data on the growth processes of GaAs layers on silicon substrates by molecular beam epitaxy are presented. The formation of a buffer Si layer in a single growth process has been found to significantly improve the crystalline quality of GaAs layers formed on its surface and to prevent the formation of antiphase domains on both off-cut toward the [110] direction and singular Si(100) substrates. It has been demonstrated that the use of cyclic thermal annealing at temperatures 350–660°C in the flow of arsenic atoms makes it possible to reduce the number of threading dislocations and increase the smoothness of the GaAs layers surface. Possible mechanisms that lead to improvement in the quality of the surface layers of GaAs are considered. It is shown that for the thus obtained GaAs layers of submicron thickness on singular Si(100) substrates the mean square surface roughness is 1.9 nm. The principal possibility of using thin GaAs layers on silicon as templates for forming on them light-emitting semiconductor heterostructures with active area based on self-organizing InAs quantum dots and InGaAs quantum well is presented. It is found that the resulting materials exhibit photoluminescence at an emission wavelength of 1.2 µm at room temperature. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires have inspired plenty of novel nanotechnology device concepts in photonics, electronics, and sensing, owing to their unique functionalities and integrability in heterogeneous platforms. Lattice‐mismatched core/shell heterostructures, in particular, open new avenues for strain engineering and material properties modification. A notable case is the widely tunable tensile strain in the core of GaAs/InxAl1‐xAs core/shell nanowires, which can be used to tailor the GaAs bandgap for applications across near‐infrared, like optical fiber telecommunication, imaging, photovoltaics, etc. As it is shown here, though, the bandgap narrowing under high tensile strain in the GaAs core is accompanied by fast non‐radiative recombination, which is undesirable for any device application. The limiting role of the lattice‐mismatched core/shell interface is revealed, and a novel core/dual‐shell heterostructure that employs an intermediate AlyGa1‐yAs shell (spacer) is proposed. This spacer decouples the GaAs/AlyGa1‐yAs interface, which confines electrons and holes into GaAs, from the lattice‐mismatched AlyGa1‐yAs/InxAl1‐xAs one, whereas the strain in GaAs is unaffected. Choosing the optimal spacer thickness, the photoluminescence yield increases significantly, with longer emission decay lifetimes and slower carrier cooling rates. Besides unlocking the potential of GaAs for photonic applications across near‐infrared, the proposed heterostructure concept can also be adopted for other material systems. [ABSTRACT FROM AUTHOR]

In this study, the frequency down-conversion of terahertz waves is analytically and experimentally demonstrated at the temporal boundaries within a GaAs waveguide. The temporal boundary is established by photoexciting the top surface of the waveguide, thereby instantaneously increasing its electrical conductivity. This photoexcited waveguide supports a transverse electromagnetic (TEM) mode with a frequency lower than those of the transverse magnetic (TM) modes present in the original waveguide. At the temporal boundary, the incident TM mode couples with the TEM mode, resulting in frequency down-conversion. Subtracting the propagation loss from the frequency-converted components indicates that the frequency conversion occurs with an efficiency consistent with the analytical predictions. The propagation loss is primarily due to ohmic loss, caused by the finite electrical conductivity of the photoexcited region. Given that the frequency of transverse electric modes is up-converted at the temporal boundary, our findings suggest that the direction of frequency conversion (upward or downward) can be controlled by manipulating the incident polarization. The polarization-dependent frequency conversion in waveguides holds significant potential for applications in devices designed for the interconversion of terahertz signals across various frequency channels. This capability is instrumental in the development of frequency-division-multiplexed terahertz wave communication systems, thereby enabling high data transfer rates. [ABSTRACT FROM AUTHOR]

We report on the fabrication of a novel design of GaAs/(In,Ga)As/GaAs radial nanowire heterostructures on a Si 111 substrate, where, for the first time, the growth of inhomogeneous shells on a lattice mismatched core results in straight nanowires instead of bent. Nanowire bending caused by axial tensile strain induced by the (In,Ga)As shell on the GaAs core is reversed by axial compressive strain caused by the GaAs outer shell on the (In,Ga)As shell. Progressive nanowire bending and reverse bending in addition to the axial strain evolution during the two processes are accessed by in situ by x-ray diffraction. The diameter of the core, thicknesses of the shells, as well as the indium concentration and distribution within the (In,Ga)As quantum well are revealed by 2D energy dispersive x-ray spectroscopy using a transmission electron microscope. Shell(s) growth on one side of the core without substrate rotation results in planar-like radial heterostructures in the form of free standing straight nanowires. [ABSTRACT FROM AUTHOR]

This study attempts to understand and elucidate the factors limiting/determining the external quantum efficiency (EQE) of light‐emitting diodes (LEDs) depending on material systems, i.e., III‐arsenide (GaAs), III‐phosphide (AlGaInP), and III‐nitride (GaInN), via the temperature measurements (30–500 K). The behaviors of EQEs are investigated carefully in terms of the thermal droop and efficiency droop, revealing that the thermal droop in the AlGaInP and GaAs LEDs, while the efficiency droop in the GaInN LEDs, is a critical factor limiting the EQE. To deepen the insight, the EQE is separated into internal quantum efficiency (IQE) and light‐extraction efficiency (LEE). Further, the IQE is separated into radiative efficiency (RE) and injection efficiency (IE). The analysis shows that the LEE plays a significant role in the thermal droop for the AlGaInP and GaAs LEDs. Meanwhile, the IE and RE play a significant role in the EQE reduction of the blue and red LEDs at high temperatures and high current injection. [ABSTRACT FROM AUTHOR]

In this paper, we present a unified model for gallium arsenide (GaAs) based on ab initio simulations which characterizes its terahertz (THz) properties when excited by optical pump. We use density functional perturbation theory to calculate the dielectric properties of GaAs, and investigate the relaxation time of photo-excited GaAs through electron–phonon interactions. In light of the complexities arising from the mixed absorption mechanisms and the sensitivity of GaAs to laser parameters, we have developed a method that leverages time-dependent density functional theory and Boltzmann transport theory. This approach enables us to establish an accurate relationship between the pump laser intensity and the carrier concentration by introducing the percentage of excited electrons, facilitating the quantitative characterization of GaAs's response under different optical pump intensities. Using the microscopic material parameters solved by first principles, we develop a unified Drude model to describe the macroscopic electromagnetic responses of photo-excited GaAs. We simulate several reported numerical examples of photo-excited GaAs, including a GaAs wafer and GaAs-based THz metamaterial modulators, to validate the proposed unified model as a reliable approach for predicting the THz properties of GaAs. The good agreement between the simulation and measurement results demonstrates that our model successfully captures the dynamic responses of photo-generated carriers and provides guidance for the design of optoelectronic devices based on GaAs. Furthermore, our modeling approach based on ab initio simulations is free from empirical parameters, providing a solid THz modeling method for other photo-excited semiconductor materials. [ABSTRACT FROM AUTHOR]

The progress in semiconductor technology has played a crucial role in enhancing human existence by introducing significant innovations. The pursuit of high-performance devices utilizing novel materials has emerged as a crucial avenue for surmounting the existing limitations of silicon-based technologies. This paper presents an evaluation of the diverse short channel effects (SCEs) exhibited by the double gate n-FinFET structure, considering the influence of temperature on channel materials using metal gate (MG) as Gallium Arsenide (GaAs) alongside High-K dielectric oxide materials such as Hafnium Oxide (HfO2), Lanthanum Oxide (La2O3) and Lanthanum Aluminum Oxide (LaAlO3) in comparison with traditional Silicon Dioxide (SiO2). The investigation and presentation of the impact of gate length (Lg), channel width (Wch), doping, and varying Temperature (275k-450k) on several short channel effects (SCEs), namely Drain Induced Barrier Lowering (DIBL), Subthreshold Slope (SS), threshold voltage (Vth) roll-off, Transconductance (gm) and ON-OFF current ratio (ION / IOFF) have been thoroughly examined using the aforementioned materials. The utilization of FinFET technology using HK-MG presents notable benefits in terms of mitigating the subthreshold swing while concurrently maintaining a low drain-induced barrier lowering (DIBL) effect. [ABSTRACT FROM AUTHOR]

A very compact three‐pole bandpass filter with wide upper stopband is proposed and implemented by gallium arsenide integrated passive device technology. By organizing inductor and capacitor in parallel with an LC series network, a dual‐frequency bandstop structure is constructed in the first step to achieve transmission zeros (TZs). Then, the lowpass capacitor network and highpass inductor network are wisely cascaded with the bandstop structure, thus to the realization of three‐pole bandpass filter with a wide upper stopband. Based on the even‐/odd‐mode analysis, theoretical equations for the in‐band resonances and out‐of‐band TZs are given. Then, one filter prototype centered at 4.4 GHz with 3‐dB fractional bandwidth of 45.5% is designed, fabricated, and measured. Both simulated and measured results indicate that the proposed filter exhibits a wide stopband rejection of 25 dB from 6.4 to 22.8 GHz as well as a very compact size about 0.026λg × 0.031λg. [ABSTRACT FROM AUTHOR]

This article centers its attention on the phenomenon of electrostatics, linearity, analogue, and RF performance of a 0.5 μm × (2 × 100) μm double heterojunction AlGaAs/InGaAs/GaAs pHEMT using on‐wafer DC and RF measurements up to 50 GHz. With a high ION/IOFF ratio (1.21 × 107) and low subthreshold slope (72.7 mV/dec), a flat and high transconductance over a wide range of Vgs has been achieved for the tested device. Furthermore, the input intercept and higher‐order voltage intercept point both attained large values with low intermodulation and harmonic distortion. Regarding RF parameters, the intrinsic gain has been achieved up to 28 dB. The GBW up to 750 GHz was attained, with the highest fT and fmax values being 24.5 GHz and 99.3 GHz, respectively. Since the device has very low intrinsic capacitance, parameters like TFP, GFP, and GTFP also showed excellent results. The high intrinsic gain and TGF indicate ample potential of the device for use as an amplifier. Investigating the parameters reveals the device to have very good linearity and amplifying capability. [ABSTRACT FROM AUTHOR]

In order to address the challenges of complex process and low precision in traditional device modeling, double hidden layer back propagation neural network (BPNN) are trained using the conjugate gradient (CG) algorithm and the Levenberg–Marquardt (LM) algorithm, the CG‐BPNN and LM‐BPNN models of small signal for gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) are obtained and analyzed here. At first, the scattering parameters (S‐parameters) of GaAs pHEMT are divided into training set and test set randomly. Experimental results show that the CG‐BPNN model is better than another S‐parameters when predicting ImS12 with mean square error (MSE) of 7.6632e‐06, while LM‐BPNN model predicts ImS12 with MSE of 2.4672e‐06. Meanwhile, the MSE of CG‐BPNN model is higher than LM‐BPNN model when predicting all the S‐parameters. In addition, it shows a smaller fluctuation range for the error curve of LM‐BPNN model, which is more stable than the CG‐BPNN model. Therefore, the double hidden layer LM‐BPNN model is the better choice to characterize the small signal of GaAs pHEMT. [ABSTRACT FROM AUTHOR]