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The generation of high-voltage ultrafast electrical pulses has significant potential for application in ultrawideband microwave sources, terahertz technology, and inertial confinement fusion. However, there is still a lack of the generation of high-voltage ultrafast electrical pulses with greater peak amplitudes and faster pulse widths and ultrafast characteristics. In this paper, a linear low-temperature gallium arsenide photoconductive semiconductor switch (LT-GaAs PCSS) is developed using the ps-scale carrier lifetime of low-temperature gallium arsenide (LT-GaAs). The generation of ultrafast electrical pulses with a pulse width of 0.5 ns and a voltage amplitude of 1 kV is achieved by triggering a pulsed laser with a wavelength of 1064 nm, a single pulse energy of 70 μJ, and a pulse width of 30 ps. The impact of parameters, such as bias electric field, laser pulse energy, and transmission line length, on the ultrafast characteristics of the output electric pulse of the LT-GaAs PCSS is investigated through a synthesis of experimental and simulation approaches. The results show that (1) in linear conditions, the output pulse amplitude is mainly determined by the bias voltage and laser pulse energy, and the output pulse amplitude is also affected by conductor and dielectric attenuation in the transmission line; (2) the falling edge is determined by the carrier lifetime. Because of the absorption depth at 1064 nm and the carrier lifetime of semi-insulating gallium arsenide material, the output electrical pulse has a trailing edge; (3) the bias voltage and laser pulse energy can improve voltage transmission efficiency, and the saturation of voltage transmission efficiency is caused by the saturation of photon absorption in LT-GaAs material. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

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]

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 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]

The article "A 1 kV sub-nanosecond electrical pulse generated by a linear GaAs photoconductive semiconductor switch and its characterization" in the Journal of Applied Physics contained errors in Eqs. (4), (5), (7), and (12) as well as a typo on page 4, which were corrected in the online version on 13 January 2025. The corrected equations are provided in the article, authored by Hongqi Wang, Wei Shi, Cheng Ma, Meilin Wu, Jiang Tao, and Kaipeng Chen. AIP Publishing issued an apology for the errors in the original publication. [Extracted from the article]

Nanostructured negative electron affinity GaAs photocathodes for a polarized electron source are studied using finite difference time domain optical simulation. The structures studied are nanosquare columns, truncated nanocones, and truncated nanopyramids. Mie-type resonances in the 700–800 nm waveband, suitable for generation of polarized electrons, are identified. At resonance wavelengths, the nanostructures can absorb up to 99% of the incident light. For nanosquare columns and truncated nanocones, the maximum quantum efficiency (QE) at 780 nm obtained from simulation is 27%, whereas for simulated nanopyramids, the QE is ∼21%. The high photocathode quantum efficiency is due to the shift of Mie resonance toward the longer wavelength, leading to increased light absorption. The field profile distribution shows the excitation of dipole and quadrupole modes within the nanostructures at resonant frequencies. This leads to enhanced photoabsorption and photoelectron generation closer to emission surfaces than for a flat photocathode. The enhanced photoabsorption and reduced electron transport distance for the nanostructured photocathode enhance its QE compared to that for the flat surface wafer. [ABSTRACT FROM AUTHOR]

We investigated the effects of thermal cycle annealing (TCA) at high temperatures on the defect density and morphology of GaAs epilayers grown on (001) Si substrates. Several types of TCA combined with dislocation filter layers (DFLs) were introduced to reduce the defect densities in the GaAs grown on Si substrates. Plan-view transmission electron microscopy shows that the defect density of a 2.7 μm-thick GaAs/Si template with optimized TCA and DFLs is 1.4 × 107 cm−2, lower than a 1.1 μm-thick GaAs/Si template by a factor of 40. The surface roughness of the optimized GaAs/Si template is 1.3 nm after insertion of the DFLs. Additionally, optically pumped InP quantum dot micro-disk lasers (MDLs) were fabricated on these GaAs/Si templates to evaluate the template quality. Room-temperature continuous-wave lasing of 1.5 μm-diameter MDLs was observed, with ultralow lasing thresholds ranging from 0.5 to 2 μW. [ABSTRACT FROM AUTHOR]

Pulse responses of different materials commonly used as electron sources in photoinjectors have been determined. Thin film photocathodes, such as strained GaAs/GaAsP superlattice and K2CsSb, produce fast responses. The emission intensity at time scales comparable with the acceptance of electron accelerators is found to be reasonably low, which is an advantage for operation at high beam powers. The temporal responses of these cathodes are compared with the response of bulk GaAs. [ABSTRACT FROM AUTHOR]

A process sequence enabling the large-area fabrication of nanopillar-patterned semiconductor templates for selective-area heteroepitaxy is developed. Herein, the nanopillar tops surrounded by a SiNx mask film serve as nanoscale growth areas. The molecular beam epitaxial growth of InAs on such patterned GaAs (111) A templates is investigated by means of electron microscopy. It is found that defect-free nanoscale InAs islands grow selectively on the nanopillar tops at a substrate temperature of 425 °C. High-angle annular dark-field scanning transmission electron microscopy imaging reveals that for a growth temperature of 400 °C, the InAs islands show a tendency to form wurtzite phase arms extending along the lateral ⟨ 11 2 ¯ ⟩ directions from the central zinc blende region of the islands. This is ascribed to a temporary self-catalyzed vapor–liquid–solid growth on { 11 1 ¯ } B facets, which leads to a kinetically induced preference for the nucleation of the wurtzite phase driven by the local, instantaneous V/III ratio, and to a concomitant reduction of surface energy of the nanoscale diameter arms. [ABSTRACT FROM AUTHOR]

We investigated the radiation damage to carrier lifetimes in the neutral and depletion regions of the InGaP and GaAs subcells of an InGaP/GaAs/Ge triple-junction solar cell. It is difficult to clarify the degradation characteristics of the carrier lifetime in each region using the conventional analysis method (e.g., the dark current–voltage characteristic analysis), so we propose a novel method using the internal luminescence efficiency. The radiation damage coefficients for the carrier lifetimes in the neutral region of InGaP and GaAs subcells were two or three orders of magnitude larger than those in the depletion region. This result suggests that the effective radiation-induced defects in the regions, which significantly impact a solar cell's electrical characteristics, differ. This paper discusses the effective radiation-induced defects that contribute to the output degradation in each region. We compare the radiation damage coefficients for the carrier lifetimes obtained in our analysis, the product of the capture cross section, and the defect introduction coefficient of each defect reported in previous studies. [ABSTRACT FROM AUTHOR]

The damage induced in GaAs crystals irradiated with dual-ion beam (low-energy I2+ and high-energy Fe9+), producing simultaneous nuclear (Sn) and electronic (Se) energy depositions, was investigated using several characterization techniques. Analysis of the damage buildup shows that Sn alone (single 900 keV ion beam) leads, in a two-step process, to full amorphization of the irradiated layer (at a fluence of 1.5 nm−2) and to the development of a high (2.2%) elastic strain. Conversely, only one step in the disordering process is observed upon dual-ion beam irradiation (i.e., 900 keV I2+ and 27 MeV Fe9+, Sn&Se); hence, amorphization is prevented and the elastic strain remains very weak (below 0.2%). These results provide a strong evidence that, in GaAs, the electronic energy deposition can induce an efficient dynamic annealing of the damage created in collision cascades formed during nuclear energy deposition. [ABSTRACT FROM AUTHOR]

We propose a non-destructive, all-optical technique to imprint embedded lateral superlattices near semiconductor heterostructures by illuminating the samples with a stable interference pattern generated by a phase diffraction grating. We demonstrate the technique on an ultrahigh mobility GaAs/AlGaAs sample with a Si δ-doping by inducing a persistent charge redistribution at cryogenic temperatures in the doping layer containing DX-centers. Weiss commensurability oscillations in the magnetoresistance of the light-induced superlattice are observed and analyzed to obtain its characteristics. [ABSTRACT FROM AUTHOR]

This experimental study reports the morphological and optical properties of self-organized quaternary InAlGaAs quantum dots (QDs) grown on GaAs substrates. Atomic force microscopy (AFM) revealed the presence of QDs and their geometry across the sample surface, while the optical properties were verified by photoluminescence (PL) spectroscopy. Temperature-dependent PL measurements were performed for a series of samples with different indium compositions. Unlike conventional quantum well materials, the change in PL peak positions in QD structures exhibits a non-monotonic exotic dependence on temperature. Our AFM data confirm a bimodal distribution of dot sizes as corroborated by calculated thermal activation energies. A rapid decrease in the PL signal at elevated temperatures suggests that thermionic emission and interface defects are the two dominant mechanisms of carrier escape and recombination in these QD structures. Such a quaternary QD-based active region is important for realizing next-generation diode lasers with an emission wavelength shorter than 1 μm. [ABSTRACT FROM AUTHOR]

In this paper, we present the physics and design-space exploration of a novel pulse compression photoconductive switch (PCPS) using semi-insulating gallium arsenide (GaAs) operating in the negative differential mobility (NDM) regime of electron transport. We systematically quantify the relationship between the PCPS performance and various design options, including contact separation, laser energy and placement, and trap dynamics. Specifically, we report the full-width at half-maximum and the peak output current generated by the PCPS as a function of applied electrical and optical bias. We discuss the optimal spacing between the electrodes and the distance of the laser spot to the anode to achieve higher electron confinement and superior radio-frequency (RF) metrics. Reducing the laser energy is important to prevent the appearance of secondary peaks due to diffusive transport, but there exists a trade-off between the bandwidth and the maximum current of the PCPS. We also compare the PCPS response with and without trap dynamics and find that the electrostatic screening from the trap-induced space charge is time-independent when the trapping time constant is set larger than the recombination lifetime. Overall, trap dynamics are detrimental to performance, unless the compensation doping scheme to achieve semi-insulating GaAs is carefully selected. Results presented in this paper can be used by experimentalists to fine-tune the PCPS design parameters to meet the specifications of various RF applications. Moreover, our results will provide a strong theoretical basis to the measurements of PCPS devices using GaAs and other NDM materials under investigation. [ABSTRACT FROM AUTHOR]

The choice of substrate orientation for semiconductor quantum dot circuits offers opportunities for tailoring spintronic properties such as g-factors for specific functionality. Here, we demonstrate the operation of a few-electron double quantum dot circuit fabricated from a (110)-oriented GaAs quantum well. We estimate the in-plane electron g-factor from the profile of the enhanced inter-dot tunneling (leakage) current near-zero magnetic field. Spin blockade due to Pauli exclusion can block inter-dot tunneling. However, this blockade becomes inactive due to hyperfine interaction mediated spin flip-flop processes between electron spin states and the nuclear spin of the host material. The g-factor of absolute value ∼0.1 found for a magnetic field parallel to the direction [ 1 ¯ 10 ] is approximately a factor of four lower than that for comparable circuits fabricated from a material grown on widely employed standard (001) GaAs substrates and is in line with reported values determined by purely optical means for quantum well structures grown on (110) GaAs substrates. [ABSTRACT FROM AUTHOR]

The emission lines of strongly confined (211)B InAs/GaAs quantum dots (QDs), embedded in short-period GaAs/AlAs superlattices, are thoroughly characterized by a range of single-dot spectroscopy techniques, including cross correlation photon-counting measurements. Contrary to what is expected for a piezoelectric QD system, the single-dot biexciton line is found redshifted with respect to the exciton one by as many as 6 meV. This comes in striking contrast to previous reports on the same QD system, without additional confinement, where the biexciton lines always showed up at higher energies than the exciton, by 4–13 meV. In addition, two charged exciton lines are identified for the first time in a piezoelectric InAs-based QD. A positively charged (Χ+) and a negatively charged (Χ−) trion line are observed 1.5 and 7.5 meV below the neutral exciton line, respectively. Our results pave the way to an enhanced understanding of the excitonic transitions in (211)B QDs and highlight the possible role of strong confinement and accompanying correlation effects as a means to tailor the transition energies of multi-particle states in semiconductor QDs. [ABSTRACT FROM AUTHOR]

A method is proposed for calculating the diffusion length damage coefficient for minority carriers (K L) in GaAs and InGaP solar cells under electron irradiation using the Shockley–Read–Hall (SRH) model for defect-assisted recombination. In the SRH model, the damage coefficient K L is proportional to the product k σ c , where k is the defect introduction rate under particle radiation and σ c is the minority carrier capture cross section of the said defects. The introduction rate k is evaluated using the atomic theory for displacement under electron radiation, and the calculation for σ c is adapted from Henry and Lang's high-temperature multiphonon emission formulation. A linear scaling relationship is observed between k , K L and nonionizing energy loss—validated by bibliographic data in the radiation energy range E ≈ 0.7 –12 MeV. Our model reproduces the increasing trend in K L with doping, as observed in the literature, while also capturing the anisotropy between the p -type and n -type materials, with the p -type exhibiting greater radiation resistance than its n -type counterpart. The calculated K L is fed into the physical model for solar cell operation to obtain the post-irradiated I sc , V oc , P max at a given fluence Φ. The degradation of the electrical quantities is consistent with the measurements recorded in the literature. The findings show that InGaP is more radiation resistant than GaAs. It is demonstrated that calculating k not only aids in determining the degradation of solar cell parameters from first principles, but also in obtaining the empirical function for degradation: a − b log (1 + c k Φ) , used in fitting the experimental measurements. The limitations and potential scope of improvements in the model are also discussed. [ABSTRACT FROM AUTHOR]

We investigate the influence of strain and dislocations on band alignment in GaSb/GaAs quantum dot systems. Composition profiles from cross-sectional scanning tunneling microscopy images are interpolated onto a finite element mesh in order to calculate the distribution of local elastic strain, which is converted to a spatially varying band alignment using deformation potential theory. Our calculations predict that dislocation-induced strain relaxation and charging lead to significant local variations in band alignment. Furthermore, misfit strain induces a transition from a nested (type I) to a staggered (type II) band alignment. Although dislocation-induced strain relaxation prevents the type I to type II transition, electrostatic charging at dislocations induces the staggered band alignment once again. [ABSTRACT FROM AUTHOR]

The electron mobility and the dark resistivity of undoped semi-insulating GaAs have been calculated theoretically over the temperature range from 5 to 500 K by taking into consideration all indispensable scattering processes, screening effects, and impurities compensation action. The two temperature characteristic curves of electron mobility and dark resistivity both exhibit unimodality. The peak value of the mobility as high as 11.4 × 105 cm2 V−1 s−1 can be achieved at 27 K, which is more than two orders of magnitude greater than that at 300 K. We analyzed the carrier relaxation rate due to scattering by ionized impurities, acoustic deformation potential, piezoelectric, and polar optical phonons. It is found that the unusually thermal characteristic is dominated by ionized impurity scattering, piezoelectric scattering, and polar optical phonon scattering in different temperature ranges, respectively. According to the scattering theory models, the dominant position relationships between the two different carrier scatterings induced by acoustical phonons in two-dimensional GaAs layer and bulk semi-insulating GaAs are discussed, respectively. The peak value of dark resistivity is about 1.29 × 1012 Ω cm at 154 K, which is more than five orders of magnitude greater than that at 300 K. The theoretical results are in good agreement with previously published results. Moreover, the dependence of the peak value of dark resistivity on the deep and shallow donor concentrations are obtained, respectively, and the mechanisms of the dependence are discussed. Understanding of thermal properties of dark resistivity and mobility can be used to optimize GaAs-based electronic and photonic devices' performance in different temperature regimes. [ABSTRACT FROM AUTHOR]

Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy. [ABSTRACT FROM AUTHOR]

Hydride vapor phase epitaxy (HVPE) is a promising technology that can aid in the cost reduction of III-V materials and devices manufacturing, particularly high-efficiency solar cells for space and terrestrial applications. However, recent demonstrations of ultrafast growth rates (∼ 500 μ m/h) via uncracked hydrides are not well described by present models for the growth. Therefore, it is necessary to understand the kinetics of the growth process and its coupling with transport phenomena, so as to enable fast and uniform epitaxial growth. In this work, we derive a kinetic model using experimental data and integrate it into a computational fluid dynamics simulation of an HVPE growth reactor. We also modify an existing hydride cracking model that we validate against numerical simulations and experimental data. We show that the developed growth model and the improved cracking model are able to reproduce experimental growth measurements of GaAs in an existing HVPE system. [ABSTRACT FROM AUTHOR]

We report here a general theory describing photoelectron transportation dynamics in GaAs semiconductor photocathodes. Gradient doping is incorporated into the model through the inclusion of directional carrier drift. The time-evolution of electron concentration in the active layer upon the injection of an excitation pulse is solved both numerically and analytically. The predictions of the model are compared with experiments via a carrier-induced transient reflectivity change, which is measured for gradient-doped and uniform-doped photocathodes using femtosecond pump–probe reflectometry. An excellent agreement is found between the experiments and the theory, leading to the characterization of key device parameters, such as diffusion constant and electron decay rates. Comparisons are also made between uniform doping and gradient doping for their characteristics in photoelectron transportation. Doping gradient is found to be able to accelerate electron accumulation on the device surface. These results offer new insights into the dynamics of III–V photocathodes and potentially open a new avenue toward experimental characterization of device parameters. [ABSTRACT FROM AUTHOR]

We illuminate a gallium arsenide (GaAs) Gunn device and study the light-induced changes of Gunn oscillation properties. We observe that illumination leads to the modulation of the Gunn threshold voltage, the Gunn oscillation magnitude, and the coherency of Gunn oscillation, with the nature of the modulation being closely related to the position of illumination on the device. These effects are attributed to the generation of optically excited carriers, which results in the modulation of conductivity and the electric field profile along the device. The finite element method is used to simulate the change of the field profile of the Gunn device caused by illumination. We also report an unexpected phenomenon of Gunn oscillation property manipulation with an optical chopper. In addition, wavelength-dependent, power-dependent, and pulsed illumination measurements are performed to help with further understanding the observations. [ABSTRACT FROM AUTHOR]

We have systematically investigated highly mismatched AlInSb photodiodes grown on GaAs substrates operating in the mid-infrared range. A novel characterization method was introduced to analyze the recombination mechanism within an active layer of the devices, which revealed a high conductance stemming from the leaky behavior of dislocations. The introduction of a dislocation filter layer successfully reduced threading dislocations and improved resistance area product of photodiodes, leading to high detectivity at room temperature. [ABSTRACT FROM AUTHOR]

The surface Cs–O activation process directly determines quantum efficiency and stability of negative-electron-affinity photocathodes. To investigate the effects of excessive Cs and O supply on activation and to explore a more effective Cs–O activation recipe, Cs–O activation experiments of GaAs(100) photocathodes are carried out based on the current-driven solid Cs and O dispensers. By a comparison of differences in activation photocurrent, quantum efficiency, and photocurrent decay, it is found that the recipe of excessive O and non-excessive Cs is not suitable for activating GaAs photocathodes, while the recipe of continuous and completely excessive Cs along with intermittent and non-excessive O can achieve the most excellent photoemission performance, including the highest quantum efficiency in the long-wave threshold region and best stability under intense light irradiation after activation. Furthermore, this improved activation recipe with the least Cs–O alternating cycles is easier to operate. Combined with density functional calculations and dipole layer model, it is found that the activation recipe of completely excessive Cs and non-excessive O can form effective dipoles to the greatest extent, and avoid the direct interaction between As atoms and O atoms to form As–O–Ga oxides on the GaAs(100) reconstructed surface. [ABSTRACT FROM AUTHOR]

The stability of strained-layer heterostructure lasers can be assessed by their response to stimuli for the introduction of dislocations. Three-point bending at elevated temperatures has been applied to GaAs/InxGa1−xAs/GaAs heterostructures to apply such a thermomechanical stimulus. In each case, the middle-layer thickness was below the critical thickness predicted by the Matthews–Blakeslee model, so that the pre-test structures were fully strained with no observed misfit dislocations. The tensile stress of 46.4 MPa produced during the tests resulted in the formation of 60° misfit dislocations whose configurations changed according to the alignment of the bending axis. For bending in the [110] orientation, the misfit dislocations formed parallel to each other and to the bending axis. For [100] bending, they formed an orthogonal pattern with each dislocation at 45° to the bending axis. In each case, these misfit dislocations caused relaxation of the strained-layer structures, even though the unloaded structures had been considered thermodynamically stable and the test temperatures were lower than those used during the original fabrication of the structures. These findings challenge existing assumptions of strained-layer stability and have implications for the design of lasers intended to be "buried and forgotten" in optical telecommunications. [ABSTRACT FROM AUTHOR]

We fabricate gallium arsenide-based devices with a wedge-shaped tapering region connected to a rectangular-shaped region and measure the threshold voltage required to trigger the Gunn effect. The threshold voltage reduction is attributed to the focusing of the electric field toward the narrower end of the device and is effective when the device has a steep enough tapering. We also model the electric field profile for the tapered devices using an intuitive graphical approach and the finite element method and provide estimates for the threshold voltages of tapered devices. Finally, we compare the estimates to the measured values and provide possible reasons for the discrepancies. We believe the capability of threshold voltage reduction with the wedge-shaped tapering design could be useful in device applications. [ABSTRACT FROM AUTHOR]

We use time-resolved optical reflectivity with femtosecond resolution to study the ultrafast dynamics of photoexcited carriers in bulk GaAs. We observe an emergence of short-lived excitons at room temperature right after photoexcitation, in terms of a sharp dip and sub-ps lifetime in the transient reflectivity changes, as long as the pump fluence increases above a critical value F c. Our findings help understand ultrafast physics in this material. [ABSTRACT FROM AUTHOR]

A model used to simulate and optimize the performance of nanowire-based betavoltaic generators is developed. The optimum nanowire array geometry is established for devices made of silicon, gallium arsenide, and gallium phosphide for both nickel-63 and tritium sources by computing the energy capture efficiency for each case. The captured power for nanowire devices is shown to be drastically greater compared to planar betavoltaic generators with maximum improvement factors of approximately 7, 3, 5, and 9 for devices utilizing radioisotope sources of nickel-63, nickel citrate, tritium, and tritiated butyl, respectively. In addition, nanowire devices do not suffer from self-shielding effects, a large limitation in conventional, planar betavoltaics. By coupling the spatial distribution of electron–hole pair generation rate calculated from Monte Carlo simulations and a semiconductor charge-transport model, the diode design is optimized for the maximum power output. The top performing devices, utilizing a tritium source, exhibited an output power of approximately 4, 6, and 2 μW cm−2 for silicon, gallium arsenide, and gallium phosphide, respectively. Overall device efficiencies were found to range from 4% to 10%, surpassing several betavoltaic devices reported in the literature. It was also found that, contrary to the traditional betavoltaic design, semiconductors with higher bandgaps do not necessarily result in the best device performance due to additional material parameters, such as surface recombination velocity. Potential improvements for nanowire-based betavoltaic generators are suggested for additional investigation. [ABSTRACT FROM AUTHOR]

We present work on a novel In0.53Ga0.47As/AlAs metamorphic asymmetric spacer layer tunnel (mASPAT) diode structure, which was grown on GaAs by solid source molecular beam epitaxy. mASPAT diodes with different mesa sizes were fabricated and tested following growth under optimal conditions. The measured I–V characteristics of these tunneling devices showed rectifying behavior resulting from the asymmetric design of the epitaxial spacer layers. The extracted curvature coefficient, junction resistance, and leakage currents at −1 V resulted in an estimated theoretical cut-off frequency f t at zero bias exceeding 180 GHz for 4 × 4 μm2 mesa devices. The obtained results demonstrate the potential use of mASPAT devices on GaAs as a low-cost alternative to devices fabricated on InP substrates for high-volume zero bias microwave and millimeter-wave detectors. [ABSTRACT FROM AUTHOR]

The absence of an efficient technology of GaAs passivation limits the use of III–V semiconductors in modern electronics. The effect reported here can possibly lead to a solution to this long standing problem. We found that an electrically conducting interfacial channel is formed when insulating metal oxide dielectrics are deposited on untreated semi-insulating GaAs wafers by reactive RF sputtering in argon/oxygen plasma. The conducting channel is n-type with a surface charge density of 107–1010 cm−2 and Hall mobility as high as 6000 cm2/V s, depending on the RF plasma excitation power and the oxygen content during deposition. The conducting channel is formed by depositing any of the tested metal oxide dielectrics: MgO, SiO2, Al2O3, and HfO2. [ABSTRACT FROM AUTHOR]

The physical characteristics of the fundamental absorption edge of semi-insulating GaAs and unintentionally doped GaSb, InAs, and InSb are examined using spectroscopic ellipsometry. A five parameter model is developed to describe the key characteristics of the absorption edge. Among these parameters are the bandgap energy, the characteristic energy of the Urbach tail, and the absorption coefficient at the bandgap energy. The results indicate that the Coulomb interaction strongly influences the shape of the band edge with progressively less influence as the bandgap energy decreases. The energy dependence of the optical transition strength is observed to be nearly constant in narrow bandgap InSb. [ABSTRACT FROM AUTHOR]

Semiconductor nanolasers based on microdisks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last few decades for on-chip light source applications. However, practical realization of low threshold, room temperature semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Furthermore, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the impact of p-type doping, compressive strain, and surface recombination on the gain spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our analysis reveals that the lasing threshold can be lowered by choosing the right doping concentration in the active III–V material combined with compressive strain. This combination of strain and p-type doping shows 100× improvement in gain and approximately five times increase in modulation bandwidth for high-speed operation. [ABSTRACT FROM AUTHOR]

Semiconductor interfaces are the backbone of modern optoelectronic devices. In terahertz (THz) science, the narrow region of an interface is crucial in the emission process. However, reports on the direct correlation of THz emission with local interface properties remain scarce owing to the inherent difficulty of using the same sample for nanoscale and macroscale studies. In this study, we combined scanning tunneling microscopy/spectroscopy (STM/STS) and THz emission spectroscopy to study the interface between a highly n + -doped and undoped gallium arsenide (GaAs). Using STS, we identify a carrier density of 1 × 10 15 cm − 3 in the low-temperature-grown GaAs (LT-GaAs) layer, which we used to visualize the energy band diagram at the interface and the surface of LT-GaAs. THz emission intensity is higher in the LT-GaAs/ n + -GaAs structures relative to semi-insulating GaAs owing to the high electric field at the interface regardless of the LT-GaAs layer thickness. Pump fluence dependence of THz showed that the thinner LT-GaAs layers saturate at lower pump fluence compared to thicker LT-GaAs and SI-GaAs. This behavior is explained by the built-in field screening by the photogenerated carriers and the free carriers from the n + -GaAs to the LT-GaAs. Our results demonstrate the utility of STM/STS to the design of semiconductor-based THz emitters. [ABSTRACT FROM AUTHOR]

The monolithic integration of III–V materials on silicon appears as the most promising, cost-effective, and versatile method for next-generation optoelectronic devices. Here, we report on GaAs metal-semiconductor-metal photodetectors integrated on an Si substrate by metal-organic chemical vapor deposition. The device architecture is based on a GaAs active layer grown on Si via ultrathin, low-temperature Ge buffer layers. The Ge-on-Si acts as a "virtual" substrate to reduce the overall structural defects in the GaAs device layers. The metal-semiconductor junction characteristics were optimized to effectively suppress the dark current and passivate the interface defects. This was achieved through the insertion of an ultrathin Al2O3 interlayer at the metal/GaAs interface. The results show that a Schottky barrier height of 0.62 eV and 0.8 eV for electrons and holes, respectively, can be achieved. Circular devices with diameters ranging from 30 to 140 μm were fabricated. The measured room temperature dark current is ∼48 nA for an applied reverse bias of 1.0 V and a device diameter of 30 μm. Additionally, the GaAs metal-semiconductor-metal structure exhibited a remarkable photoresponsivity and detectivity values of (0.54 ± 0.15) A/W and ∼4.6 × 1010 cm Hz1/2 W−1 at 5 V reverse bias, 850 nm, respectively. The proposed method offers great potential for the monolithic integration of GaAs on an Si platform. Furthermore, this technique can be extended to other III–V materials and lattice mismatched systems for high-performance multiple band optoelectronics. [ABSTRACT FROM AUTHOR]