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In this paper, we demonstrate the potential of the contactless surface photovoltage (SPV) method for fast and reliable control of GaAs-based solar cells directly on epitaxial heterostructures before metallization and photolithography processes. The magnitude of the SPV corresponds to the generated photovoltage in the photoactive region, which is related to the open circuit voltage of the cell. The focus of this investigation is the potential of dilute nitride compounds grown by low-temperature liquid-phase epitaxy (LPE) for application as intermediate cells in multijunction solar cells. First, SPV spectroscopy is used to determine the photosensitivity spectral range and bandgap of the grown dilute nitride compound layers. Further, the photovoltaic quality of the grown solar cell heterostructures is evaluated by comparing the magnitude of their SPV signals with that of a reference GaAs solar cell. A drastic reduction in the measured SPV is observed for nitrogen-containing solar cell structures, which correlates with the lowering of solar cell open-circuit voltage values measured under standard test conditions. Finally, solar cell structures based on nitrogen-free GaAsSb compounds with the same long-wavelength photosensitivity limit as GaAsSbN are grown by LPE. They show one order of magnitude higher SPV signal and, therefore, have a great potential for solar cell application. [ABSTRACT FROM AUTHOR]

To exploit the promising properties of semiconductor nanowires and ensure the uniformity required to achieve device integration, their position on the growth substrate must be controlled. This work demonstrates the direct patterning of a SiO2/Si substrate using focused ion beam (FIB) patterning to control self-catalyzed GaAsSb nanowire growth in molecular beam epitaxy (MBE). Besides position control, FIB patterning parameters influence nanowire yield, composition and structure. Total ion dose per hole is found to be the most important parameter. Yield of single nanowires ranges from ≈34% to ≈83%, with larger holes dominated by multiple nanowires per hole. Areas exposed to low ion beam doses are selectively etched by routine pre-MBE HF cleaning, enabling patterning and nanowire nucleation with minimal damage to the Si substrate. The optical and electronic properties of nanowires are found to depend on the ion dose used during patterning, indicating the potential for FIB patterning to tune nanowire properties. These findings demonstrate the possibility for a FIB lithography protocol which could provide a rapid and direct patterning process for flexible controlled nanowire growth. [ABSTRACT FROM AUTHOR]

GaAsSb semiconductor material, a ternary alloy, has long been recognized as a crucial semiconductor in the near infrared range due to its ability to finely adjust the wavelength through controlling the Sb component. In this work, we report on the pattern of orientation variation in self-catalyzed grown GaAsSb nanowires (NWs). Utilizing solid-source molecular-beam epitaxy (MBE), self-catalyzed GaAs and GaAsSb nanowires (NWs) were grown on Si (111) substrates. The influence of various Sb components on the growth direction of the nanowires in the ternary GaAsSb alloy was examined using scanning electron microscopy (SEM). The inclusion of Sb components was discovered to alter the growth direction of the nanowires, transitioning them from a vertical and inclined orientation to a configuration that encompassed vertical, inclined, and parallel orientations with respect to the Si (111) substrate. As the Sb component in GaAsSb increased, there was an increased likelihood of the nanowires growing parallel to the surface of the Si (111) substrate. A combination of X-ray diffraction (XRD) and Raman spectroscopy validated the presence of Sb components and indicated a high crystalline quality. Additionally, XRD confirmed that the Sb components aligned with the intended structure. These findings establish a solid material foundation for the development of high-performance GaAsSb-based devices. [ABSTRACT FROM AUTHOR]

This theoretical study addressed the first-order linear and third-order nonlinear optical features of GaAs/GaAsSb/GaAs V-shaped valence band quantum wells. The iterative solutions of the density matrix approach in the framework of a two-level system were used to investigate the changes in the optical absorption coefficients and refractive index. This study considered the influences of the electric field, the half-width of the well, and antimony content on the optical properties of the quantum well under intense laser fields. The first-order linear and third-order nonlinear optical responses were obtained under one-photon resonance conditions. Optical transitions appeared in Gaussian-like distributions and maximum-to-minimum schemes for linear optical absorption coefficients and refractive index changes, respectively. The nonlinear results revealed an inverse Gaussian-like and minimum-to-maximum scheme due to the negative contribution of nonlinear functions. Optical features exhibited a redshift along with an increase in the magnitude as a result of a decrease in the energy difference, and an increase in the overlap of the wavefunctions corresponding to the ground and the first-excited bound states with increasing intense laser fields. However, blueshifts and decreased magnitude were detected upon increasing the energy difference and decreasing the overlap when the electric field and the well half-width were enhanced. The results indicated that linear and third-order nonlinear optical properties remained constant due to the intent electronic characteristics by altering the antimony content. [ABSTRACT FROM AUTHOR]

We report the first study on a GaAs/GaAsSb core–shell (CS)-configured nanowire (NW)-based separate absorption, charge control, and multiplication region avalanche photodiode (APD) operating in the near-infrared (NIR) region. Heterostructure NWs consisted of GaAs and tunable band gap GaAs1–xSbx serving as the multiplication and absorption layers, respectively. A doping compensation of absorber material to boost material absorption, segment-wise annealing to suppress trap-assisted tunneling, and an intrinsic i-type and n-type combination of the hybrid axial core to suppress axial electric field are successfully adopted in this work to realize a room-temperature (RT) avalanche photodetection extending up to 1.3 μm. In an APD device operating at RT with a unity-gain responsivity of 0.2–0.25 A/W at ∼5 V, the peak gain of 160 @ 1064 nm and 18 V reverse bias, gain >50 @ 1.3 μm, are demonstrated. Thus, this work provides a foundation and prospects for exploiting greater freedom in NW photodiode design using hybrid axial and CS heterostructures. [ABSTRACT FROM AUTHOR]

In this research work, a theoretical approach has been adopted to study GaAs-based InAlAs/InGaAs/GaAsSb type-II heterostructures. The 6 × 6 k·p Hamiltonian matrix with self-consistent calculations has been carried out to calculate the wavefunctions, localization of the charge carriers (probability density of charge carriers) and their dispersed energy states (Discrete energy level) under variable quantum well width and external strain of the double quantum well heterostructure. Bulk band structures of InAlAs/GaA for different aluminium compositions have been reported. The quantum well size and external strain effect on optical gain have also been explored. Computational analysis showed the generated light has a 1.93 μm NIR lasing wavelength. At 12 GPa, optical gain reaches 7450 cm−1 and wavelength 1.93 μm. Peak gain is 5931 cm−1 for 2 nm well width. The developed type-II structure can be employed in a semiconductor laser diode operating in the NIR range as per the observed results. [ABSTRACT FROM AUTHOR]

Recent advances in the growth of III-V semiconductor nanowires (NWs) hold great promise for nanoscale optoelectronic device applications. It is established that a small amount of nitrogen (N) incorporation in III-V semiconductor NWs can effectively red-shift their wavelength of operation and tailor their electronic properties for specific applications. However, understanding the impact of N incorporation on non-equilibrium charge carrier dynamics and transport in semiconducting NWs is critical in achieving efficient semiconducting NW devices. In this work, ultrafast optical pump-terahertz probe spectroscopy has been used to study non-equilibrium carrier dynamics and transport in Te-doped GaAsSb and dilute nitride GaAsSbN NWs, with the goal of correlating these results with electrical characterization of their equilibrium photo-response under bias and low-frequency noise characteristics. Nitrogen incorporation in GaAsSb NWs led to a significant increase in the carrier scattering rate, resulting in a severe reduction in carrier mobility. Carrier recombination lifetimes of 33 ± 1 picoseconds (ps) and 147 ± 3 ps in GaAsSbN and GaAsSb NWs, respectively, were measured. The reduction in the carrier lifetime and photoinduced optical conductivities are due to the presence of N-induced defects, leading to deterioration in the electrical and optical characteristics of dilute nitride NWs relative to the non-nitride NWs. Finally, we observed a very fast rise time of ∼2 ps for both NW materials, directly impacting their potential use as high-speed photodetectors. [ABSTRACT FROM AUTHOR]

The properties of GaAsSbN and GaAsSb layers grown by liquid-phase epitaxy on n-GaAs substrates were investigated in a comparative plan with a view of their possible application in multi-junction solar cells. To avoid non-uniformity effects in the composition of these compounds with two or three different group-V volatile elements, the crystallization was carried out from finite melt with a thickness of 0.5 mm at low (<560 °C) temperatures. X-ray microanalysis and X-ray diffraction were used to determine the composition, lattice mismatch, and crystalline quality of the epitaxial layers. The morphology and surface roughness were examined by atomic force microscopy. Surface photovoltage (SPV) spectroscopy at room temperature was applied to study the optical absorption properties and the photocarrier transport in the samples. The long-wavelength photosensitivity of the GaAsSbN and GaAsSb layers, determined from their SPV spectra, is extended down to 1.2 eV. Although GaAsSb has a slightly larger lattice mismatch with the GaAs substrate compared to GaAsSbN, it presents a higher photoresponse, since, in GaAsSbN, the incorporation of N induces additional recombination centres. Therefore, GaAsSb could be an alternative to GaAsSbN for solar cell applications. [ABSTRACT FROM AUTHOR]

Avalanche photodiodes (APDs) made with the material AlGaAsSb (lattice-matched to InP) exhibit very low excess noise characteristics. We demonstrate a Separate Absorption and Multiplication APD (SAM-APD) incorporating a GaAs0.52Sb0.48 (GaAsSb) absorption region and an Al0.85Ga0.15As0.56Sb0.44 (AlGaAsSb) avalanche region. Our GaAsSb/AlGaAsSb SAM-APD exhibits a cut-off wavelength of 1.70 μm at room temperature and a responsivity of 0.39 A/W at 1.55 μm wavelength (with no antireflection coating). Temperature dependence of the breakdown voltage was obtained from avalanche gain data from multiple devices operated at 77 to 295 K. This produced a temperature coefficient of breakdown voltage of 4.31±0.33 mV/K, a factor of 10 and 5 smaller than values for comparable InP and InAlAs SAM-APDs. The very small temperature coefficient of this work is consistent with the extremely weak temperature dependence of avalanche breakdown previously observed in AlGaAsSb diodes. [ABSTRACT FROM AUTHOR]

This article reports the analysis of type-II DQW (double quantum well) heterostructure having the specified layers of GaAs 0.15 Sb 0.85 , In 0.55 Ga 0.45 As and In 0.1 Ga 0.9 As ternary compounds for the design of QW infrared photo-detector. For the optimized heterostructure, the optical characteristics (i.e. absorption spectra) are studied with the help of k.p theory. Using k.p approach the electronic and holes wavefunctions followed by E-K curves of conduction and valence bands are calculated and analyzed. In addition, the dipole and momentum matrix elements are also calculated to understand the transition mechanism which is responsible for optical absorption. For the designed In 0.1 Ga 0.9 As/GaAs 0.15 Sb 0.85 /In 0.55 Ga 0.45 As DQW heterostructure, the partial as well as overall optical absorption are calculated in the X-and Y- polarization modes. Under X- polarization mode, the peak optical absorption corresponds to two wavelengths ∼ 2700 and 3600 nm. At 2700 nm, the absorption peak is much higher and sharper than that at ∼3600 nm. In the Y- polarization mode the peak absorption is available at ∼ 2550 and 3350 nm. On behalf of the simulating results, it can be claimed that the proposed DQW heterostructure may be suitable in designing the QW photo-detectors for detecting the radiation in SWIR (short wave infrared) region, and hence useful in various kind of applications such as in industries, telecommunications, remote sensing, non-invasive diagnoses, medical imaging, spectroscopy, and environmental monitoring. [ABSTRACT FROM AUTHOR]

The impact of mole fraction variation on the RF/DC performance of GaAs1−xSbx‐based FinFET has been examined in this study. Changing the Sb mole fraction has substantial effect on the electronic band parameters of GaAs, which directly affects the device performance. Electrical properties of the device including electron density and mobility fluctuation are investigated as a function of Sb mole fraction. Additionally, device DC performance parameters such as the ION/IOFF ratio, threshold voltage, transconductance, and device node capacitance, such as Cgg and Cds, are studied using a technology computer‐aided design (TCAD) simulator. The mole fraction dependence of the gate capacitance dictates the application of the proposed FinFET in the RF and high‐frequency domains. A detailed investigation of the figures of merits such as intrinsic gain, intrinsic delay, dynamic power dissipation, power delay product, energy dissipation, and unity gain bandwidth reveals that GaAsSb can be a potential material for realization of low‐power analog and digital circuits. The proper tuning of the mole fraction can help to optimize the device performance. [ABSTRACT FROM AUTHOR]

Due to their excellent properties, ternary GaAsxSb1−x nanowires have been extensively investigated to enable various nanodevice structures. However, the surfactant effect of antimony has a notorious impact on the surface morphology and electrical properties of prepared Sb‐rich nanowires, restricting their practical utilization. Herein, through the in situ passivation effect of thiourea, highly‐crystalline, uniform, and thin GaAsxSb1−x nanowires (x ≤ 0.34) are successfully achieved. In contrast to low‐melting‐point sulfur powders typically used in surfactant‐assisted chemical vapor deposition, thiourea has a relatively higher melting point, facilitating the more controllable formation of SbxSy layer on the nanowire surface to minimize the radial growth and to stabilize the sidewalls for high‐quality Sb‐rich nanowires. When configured into field‐effect transistors, the obtained GaSb nanowires exhibit excellent device performance with a hole mobility of over 200 cm2 V−1 s−1. The optimal GaAs0.18Sb0.82 device yields an impressive responsivity of 5.4 × 104 A W−1 and an external quantum efficiency of 4.4 × 106% under near‐infrared light illumination. Importantly, the rise and decay times are as efficient as 80 and 104 µs, respectively, which are better than any values reported for GaAsSb nanowire photoconductors to date. All these results demonstrate the promising potential of GaAsxSb1−x nanowires for high‐mobility electronics and ultrafast near‐infrared optoelectronics. [ABSTRACT FROM AUTHOR]

A type-II (with broken bandgap) W-shaped nano-heterostructure having layers combination of AlSb, InAs and GaAsSb compound semiconductors has been proposed which can be utilized as high intensity lasing source in MIR (mid infrared region). For this heterostructure, a multiband band k.p Hamiltonian has been simplified to compute the required carrier’s wavefunctions, their subband structures and matrix dipole elements accountable for the probabilistic transitions which results into the high optical gain. For 2-D charge carrier density of 1.5 × 1012 cm−2, the computed results confirm that only the light hole (LH) subbands take part in optical transition in order to produce the high optical gain of the order of ~8850 /cm which corresponds to ~5.2 µm. Keeping in view its high optical gain at ~5.2 µm, the proposed type-II AlSb/InAs/GaAsSb heterostructure can be useful in the environmental monitoring, particularly important for sensing the CO2, CO and NO toxic gases available in the polluted environment. Moreover, this type-II heterostructure can also play an important role in traditional applications such as industrial, medical, MIR spectroscopy, and telecommunications applications which require ~5200 nm wavelength.

A temperature and pressure dependent tunable type-II DQW (double quantum well) heterostructure with the specific composition and combination of In 0.1 Ga 0.9 As, In 0.55 Ga 0.45 As and GaAs 0.15 Sb 0.85 layers have been designed and analyzed for the purpose of designing the QW infrared photodetector. Using k.p. theory, the optical response for the optimized heterostructure is investigated as optical absorption. The electronic and hole wavefunctions, as well as the conduction and valence band E-K curves, are computed and examined using the k.p. technique. Furthermore, the dipole matrix elements are also computed in order to comprehend the optical absorption-causing transition process. The partial and total optical absorption are computed in the X- and Y-polarization modes for the proposed QW heterostructure. The maximal optical absorption was found to meet at two wavelengths, around 2700 and 3600 nm, under the X-polarization mode. The absorption peak is stronger and significantly greater at 2700 nm than it is at about 3600 nm. The maximal absorption in the Y-polarization mode meets between about 2550 and 3350 nm. To examine the tunability, the optical absorption spectra have also been studied with variable temperature (rang: 273K–350K) and pressure (range: 0–12 GPa). With increasing temperature and pressure, the absorption peaks have been found to enhance pointedly. It may be argued that the suggested QW heterostructure may be appropriate for developing QW photodetectors to detect radiation in the shortwave infrared (SWIR) area based on the findings of the simulations. [ABSTRACT FROM AUTHOR]

The properties of GaAsSbN and GaAsSb layers grown by liquid-phase epitaxy on n-GaAs substrates were investigated in a comparative plan with a view of their possible application in multi-junction solar cells. To avoid non-uniformity effects in the composition of these compounds with two or three different group-V volatile elements, the crystallization was carried out from finite melt with a thickness of 0.5 mm at low (

We report uniform Type-II GaInAsSb/InP UTC-PDs, and compare their performance to devices fabricated with GaAsSb uniform and graded (composition and doping) absorbers of the same thickness. The quaternary UTC-PDs show a transit limited bandwidth of 274 GHz in contrast to 107 and 185 GHz for uniform and graded GaAsSb absorber UTC-PDs. Because the uniform quaternary and ternary UTC-PDs only differ in their absorber material, the findings conclusively demonstrate enhanced transport in GaInAsSb. Performance comparison to GaInAs-based devices from the literature suggest that GaInAsSb is a superior absorber material for λ = 1.55 μm high-speed photodetectors. Additionally, the external responsivity of the GaInAsSb UTC-PDs (0.094 A/W) is ∼34% higher than the GaAsSb PDs (0.070 A/W). This is the first demonstration of a quaternary GaInAsSb absorber in UTC-PDs. [ABSTRACT FROM AUTHOR]

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Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 – x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 – x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGA-PBE) and Becke–Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 – x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of GaAsxSb1 –x ternary alloys have been presented and discussed. Density functional theory (DFT) computation based on the full-potential (linearized) augmented plane-wave (FP-LAPW) method has been utilized to calculate the Density of States (DOS) and the band structure of ternary alloys GaAsxSb1 –x (x = 0, 0.25, 0.50, 0.75, 1). The calculations were performed using the exchange-correlation energy functional from Perdew, Burke, and Ernzerhof, a generalized-gradient approximation (GGAPBE) and Becke-Johnson exchange potential with local-density approximation (BJLDA) available within the framework of WIEN2k code. As compared to PBE, the results obtained from BJLDA are in close agreement with other experimental works. The DOS results show a reduction in bandgap as the Sb fraction is increased in GaAsxSb1 –x ternary alloys. The bandgap obtained by PBE and BJLDA are found to deviate from Vegard's law, i.e., it doesn't vary linearly with composition. However, the bandgap obtained by BJLD is found to closely match Vegard's law when the bowing parameter is considered. [ABSTRACT FROM AUTHOR]

The key objective of this research paper is to design a type-II nano-heterostructure which could emit the radiations of the wavelength ˜1.55 μm. Here, we have proposed and designed a novel type-II "W" shaped InAlAs/InGaAs/GaAsSb nanoscale heterostructure and simulated its optical gain characteristics theoretically with the help k.p method by solving a 6 × 6 Luttinger-Kohn Hamiltonian for determining the carrier's localities within the heterostructure. The other calculations have been performed to determine the dispersion of carrier's energies, dipole transition elements and the optical gain characteristics. Finally, the simulated results clarified that the designed heterostructure is competent to emit the radiations of ˜1.55 μm wavelength (wavelength of near infrared region) and can be utilized in optical fiber communication systems. [ABSTRACT FROM AUTHOR]

Abstract The optical quality enhancement of a GaAs template grown on Silicon substrate using InGaAs/GaAs Dislocation Filters (DFs) combined with an annealing step have been assessed optically using Photoluminescence (PL) of embedded InAs/InGaAs QDs within a GaAs matrix. An annealing temperature after the growth of the DFs of 690 °C was shown to be optimum, giving an enhanced PL emission from the embedded InAs QDs in terms of intensity and Full Width at Half Maximum (FWHM). InAs quantum dots capped with GaAsSb grown at different temperatures were grown on the optimized GaAs template on Si. The prepared samples were characterized by PL, Atomic Force Microscopy (AFM), excitation power and dependent PL at 77 K and 300 K. At 77 K, the InAs/GaAsSb grown at 484 °C showed a type II band alignment with an emission wavelength of 1297 nm, which is shorter than the emission obtained from the reference sample, where the GaAsSb-capped dots were grown on GaAs (1357 nm). By reducing the GaAsSb capping layer growth temperatures to 465 °C and 450 °C, the wavelength at 77 K was extended to 1375 nm and 1480 nm respectively, resulting from an increased Sb content in the capping layer. At 300 K, a long wavelength emission of 1623 nm have been achieved. Highlights • GaAs template optimization on Si using dislocation filters and in-situ annealing. • Growth of InAs/GaAsSb QDs on the prepared GaAs template. • The InAs/GaAsSb QDs grown at 484 °C showed a type II emission with λ = 1297 nm at 77 K. • Extension of λ to 1375 nm and 1480 nm at 77 K for GaAsSb grown at 465 °C and 450 °C. • Emission wavelength of 1623 nm from InAs/GaAsSb QDs grown on Si substrate at 300 K. [ABSTRACT FROM AUTHOR]

During the last few years, there has been renewed interest in the monolithic integration of gold-free, Ternary III–As Antimonide (III–As–Sb) compound semiconductor materials on complementary metal-oxide-semiconductor (CMOS)—compatible silicon substrate to exploit its scalability, and relative abundance in high-performance and cost-effective integrated circuits based on the well-established technology. Ternary III–As–Sb nanowires (NWs) hold enormous promise for the fabrication of high-performance optoelectronic nanodevices with tunable bandgap. However, the direct epitaxial growth of gold-free ternary III–As–Sb NWs on silicon is extremely challenging, due to the surfactant effect of Sb. This review highlights the recent progress towards the monolithic integration of III–As–Sb NWs on Si. First, a comprehensive and in-depth review of recent progress made in the gold-free growth of III–As–Sb NWs directly on Si is explicated, followed by a detailed description of the root cause of Sb surfactant effect and its influence on the morphology and structural properties of Au-free ternary III–As–Sb NWs. Then, the various strategies that have been successfully deployed for mitigating the Sb surfactant effect for enhanced Sb incorporation are highlighted. Finally, recent advances made in the development of CMOS compatible, Ternary III–As–Sb NWs based, high-performance optoelectronic devices are elucidated.

We report a “Type-II” metal–organic chemical vapor deposition (MOCVD)-grown compositionally graded quaternary base InP/GaInAsSb/InP double heterojunction bipolar transistor (DHBT) with simultaneous cutoff frequencies ${f}_{\text {T}}/{f} _{\text {MAX}}$ = 547/784 GHz. Compositional grading of the As/In mole fractions enables stronger quasi-electric fields in the base and favors better RF performance. Consideration of the higher bandstructure reveals new insights on the performance limits of “Type-II” DHBTs: Indium incorporation in a GaAsSb base appears to increase the efficiency of electron injection from the base into the InP collector. The present results correspond to the fastest MOCVD-grown quaternary base DHBTs reported to date for a device with ${f} _{\text {MAX}}>{f}_{\text {T}}$. [ABSTRACT FROM AUTHOR]

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm2 (75 μJ/cm2 per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance. [ABSTRACT FROM AUTHOR]

We present and discuss the performance characteristics of InP-based p-i-n photodiodes (PDs) with InGaAs/GaAsSb type-II multiple quantum wells absorption regions designed to absorb light at mid-infrared wavelengths. Top-illuminated and waveguide-integrated PDs are fabricated with dark currents as low as 100 nA at −2 V, an external responsivity as high as 0.27 A/Wat 2 μm and 0.3 A/Wat 1.55 μm, and a 3-dB bandwidth of 3.5 GHz at 2 μm. [ABSTRACT FROM AUTHOR]

A multi band (particularly, six band) k. p approach has been adopted for modelling the GaAsSb/InAs/AlSb W-shaped quantum well (QW)-heterostructure (a type-II with broken bandgap band alignment) and simulation of behaviour of optical gain characteristics under uni- and bi-axial pressures. The motivation behind designing such QW heterostructure is its high optical gain in MIR (mid infrared region) with noteworthy tuneable optical characteristics. The tuneable characteristics under uni-axial (100) and (001) pressure and bi-axial (110) pressure have been studied through the simplification of a multiband band k. p Hamiltonian. For all the directional pressures, the pressure range was fixed from 1 GPa to 3 GPa (with the interval of 0.5 GPa). For the (100) directional pressure, a significant increase in the gain (from 3570 to 7800/cm) was noted showing the red shifted wavelength with increasing order of pressure; while (001) directed pressure has caused to reduce the gain (3550–1158/cm) with red shifted wavelength. The (110) directed pressure has also caused to enhance the gain considerably (2550–7597/cm) with change in wavelength towards high wavelength. The study of gain characteristics was performed considering 1.5 × 1012 cm−2 2-D charge carrier density, which proves the tunability of the designed heterostructure in various tuneable optoelectronic devices. • Optical gain characteristics of GaAsSb/InAs heterostructure under variable pressures by k.p method. • The tuneable characteristics under uni-axial (100) and (001) pressure and bi-axial (110) pressure. • Increase in gain by applying the pressure along (100) and (110) while reduction in gain by pressure along (001). • For all types of applied pressures, wavelength was found to shift in long wavelength region. • This study confirms the noteworthy the tuneable character of the designed heterostructure. [ABSTRACT FROM AUTHOR]

Capping InAs/GaAs quantum dots (QDs) with a thin GaAsSb layer alters the QDs structural properties, leading to considerable changes in their optical properties. The increase of the Sb content induces a redshift of the emission energies, indicating a change in the buried QDs shape and size. The presence of well-defined ground- and excited-state emission bands in all the photoluminescence spectra allow an accurate estimation of the buried QDs size and shape by numerical evaluation and tuning of the theoretical emission energies. For an Sb content below 14%, the QDs are found to have a type I band alignment with a truncated height pyramidal form. However, for higher Sb content (22%), the QDs are present in a full pyramidal shape. The observed behavior is interpreted in terms of increasing prevention of InAs QDs decomposition with increasing the Sb content in the cap layer.

Designing of a type-II nanoscale heterostructure and simulating their optical properties is critical for many applications and remains a challenge. This paper reports designing of a complex type – II ‘W’ shaped symmetric InGaAsP/GaAsSb nano-scale heterostructure grown on InP substrate and mechanism of the transitions taking place within the heterostructure which are responsible for optical properties. In addition, the band alignment, optical gain and lasing wavelength are also studied under the effect of applied external electric field ranging from 10 to 200 kV/cm and variable temperature. On the basis of outcome of the calculations, the proposed heterostructure can be claimed to show a very high optical gain (∼8000/cm) within the MIR (mid infrared) region. Moreover, the results achieved in the study suggest that the application of the both variable temperature and applied external electric field on the heterostructure can control the optical gain as well as lasing wavelength linearly. Due to the linear behavior of the proposed heterostructure, the tunable type –II InGaAsP/GaAsSb nano-scale heterostructure can be claimed as a very suitable heterostructure for the designing of photovoltaic devices operating in the IR region. [ABSTRACT FROM AUTHOR]

Quaternary and ternary alloy semiconductors offer an extra degree of flexibility in terms of bandgap tuning. Modifications in the wave functions and alterations in optical transitions in quaternary and ternary QW (quantum well) heterostructures due to external uniaxial strain provide valuable insights on the characteristics of the heterostructure. This paper reports the optical gain in strained InGaAsP/GaAsSb type-II QW heterostructure (well width = 20 Å) under external uniaxial strain at room temperature (300 K). The entire heterostructure is supposed to be grown on InP substrate pseudomorphically. Band structure, wave functions, energy dispersion and momentum matrix elements of the heterostructure have been computed. 6 × 6 diagonalised k → · p → Hamiltonian matrix of the system is evaluated and Luttinger-Kohn model has been applied for the band structure and wavefunction calculations. TE mode optical gain spectrum in the QW-heterostructure under uniaxial strain along [110] is calculated. Optical gain of the heterostructure as a function of 2D carrier density and temperature variation is investigated. The variation of the peak optical gain as a function of As and Sb fractions in InGaAsP as a barrier and GaAsSb as a well respectively is exhibited. For a charge carrier injection of 5 × 10 12 / cm 2 , the TE optical gain is 3952 cm − 1 at room temperature under no external uniaxial strain. Significant increase in TE mode optical gain is observed under high external uniaxial strain (1, 5 and 10 GPa) along [110] within IR (Infrared region) region. [ABSTRACT FROM AUTHOR]

Semiconducting heterostructures offer an extra degree of flexibility in terms of tuning of optical gain and transition energies or wavelengths. Modifications in the wave functions and alterations in optical transitions in binary and ternary QW (quantum well) heterostructures due to external uniaxial strain provide valuable insights on the optical characteristics of the heterostructure. In this paper, we have reported the effect of uniaxial strain along [001], [100] and [110] on the optical properties such as optical gain, and optical transition energies of W − shaped complex type-II InGaAs/InAs/GaAsSb nano-scale heterostructure consisting of two quantum wells of InAs material using the six band k.p theory. On the basis of results obtained in the work, it can be reported that the TE and TM optical gain can be enhanced by application of uniaxial strain along [110] only. It is also reported that application of strain along [001] is useful for improvement of TE optical gain while strain along [100] is useful for TM optical gain. Thus, for the type-II InGaAs/InAs/GaAsSb nano-heterostructure TE and TM gain and as well as transition energies can be controlled by the application of uniaxial strain along the choice of direction. [ABSTRACT FROM AUTHOR]

This paper presents Si/SiGe:C and InP/GaAsSb HBTs which feature specific assets to address submillimeter-wave and THz applications. Process and modeling status and challenges are reviewed. The specific topics of thermal and substrate effects, reliability, and HF measurements are also discussed. [ABSTRACT FROM PUBLISHER]

We focused on design of suitable underlying and covering layers of InAs/GaAs quantum dots (QDs) with the aim to increase the carrier extraction rate in the QD solar cell structures. Covering QDs by a GaAsSb strain reducing layer (SRL) with type II band alignment significantly improves photogenerated carrier extraction from InAs QDs. An additional thin InGaAs SRL below InAs QDs further enhances the extraction of photogenerated carriers. Properties of QD structures without any SRL, with GaAsSb covering SRL, and with combination of thin below-QDs InGaAs and GaAsSb covering SRLs are compared and the mechanism of carrier extraction is discussed. We showed that thin below-QDs InGaAs SRL together with increasing profile of antimony concentration in covering GaAsSb SRL can significantly improve the resulting properties of solar cell structures with InAs QDs. [ABSTRACT FROM AUTHOR]

Annealing effects on the properties of InGaAsN/GaAsSb type-II quantum well (QW) diodes grown on InP substrates by molecular beam epitaxy (MBE) were studied. It was found that the peak of electroluminescence (EL) shows drastic red-shift and the reverse-biased current of the current-voltage ( I- V) characteristic of the type-II QW diode increases by the annealing. In addition, we found that the electron effective mass of the InGaAsN layer of the type-II InGaAsN/GaAsSb multiple quantum wells (MQWs) estimated by the temperature dependence of the amplitude of the Shubnikov-de Haas (SdH) oscillations decreases by the annealing. The mechanism of the observed annealing effects was discussed. [ABSTRACT FROM AUTHOR]

As an important candidate for novel infrared semiconductor lasers, the optical properties of GaAsSb-based multiple quantum wells (MQWs) are crucial. The temperature- and excitation power-dependent photoluminescence (PL) spectra of the GaAs0.92Sb0.08/Al0.2Ga0.8As MQWs, which were grown by molecular beam epitaxy, were investigated and are detailed in this work. Two competitive peaks were observed from 40 K to 90 K. The peak located at the low-energy shoulder was confirmed to be localized states emission (LE) and the high-energy side peak was confirmed to be free-carrier emission by its temperature-dependent emission peak position. It is observed that the LE peak exhibited a blueshift with the increase of laser excitation power, which can be ascribed to the band filling effect of localized states. Our studies have great significance for application of GaAsSb-based MQWs in infrared semiconductor lasers. [ABSTRACT FROM AUTHOR]

We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb barrier layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb barrier layer also results in a smoother surface morphology with its root-mean-square roughness of 0.7 nm due to the surfactant effect of Sb. Using a step-graded GaAsSb and AlGaAsSb metamorphic buffer layer, a 200-nm p-type In0.53Ga0.47As layer grown on Ge exhibits a hole mobility of 38 cm2 V−1 s−1 with a hole concentration of 2.6 × 1019 cm−3 at 300 K and 53 cm2 V−1 s−1 with a hole concentration of 1.2 × 1019 cm−3 at 77 K. [ABSTRACT FROM AUTHOR]

This work reports on the benefits from using thin GaAsSb capping layers (CLs) on InAs/GaAs quantum dot (QD) solar cells. The application of such CLs allows the tunability of the QD ground state, switching the QD-CL band alignment from type I to type II for high Sb contents and extending the photoresponse beyond 1.5 µm. Two different structures with ~10% and ~20% Sb contents in the CL (type-I and type-II band alignments, respectively) are explored, leading to efficiency improvements over a reference InAs/GaAs QD solar cell of 20% and 10%, respectively. In general, a significant increase in short-circuit current density (J sc ) is observed, partially due to the extended photocurrent spectrum and the additional contribution of the CL itself. Particularly, for a moderate Sb content, an improved carrier collection efficiency is also found to be a main reason for the J sc increase. Calculations from an 8×8 k·p method suggest the attribution of such an improvement to longer carrier lifetimes in the wetting layer-CL structure due to the transition to a type-II band alignment. Open-circuit voltages (V oc ) exceeding that of a reference QD solar cell are demonstrated under light concentration using GaAsSb CLs, which proves that the V oc is not limited by the low bandgap CLs. Moreover, the highest value is obtained for the high Sb content type-II structure, despite the higher accumulation of strain and the lower effective bandgap. Indeed, the faster V oc increase with light power found in the latter case leads to an V oc even larger than the effective bandgap. [ABSTRACT FROM AUTHOR]

Alterations in optical transitions and distortions in wave symmetry in nano-scale QW (quantum well) heterostructures are seen due to external uniaxial strain under different polarizations. This paper reports the anisotropy phenomena and optical gain improvement realized in In 0.3 Ga 0.7 As/GaAs 0.4 Sb 0.6 type-II QW-heterostructure (well width = 20 Å) under uniaxial strain in the SWIR (short wave infra red) region. The detailed study of the band structure, wave functions associated with the charge carriers in the respective bands and optical gain under electromagnetic field perturbation is reported. The 6 × 6 diagonal k → · p → Hamiltonian matrix is evaluated and Luttinger-Kohn model is used for the band structure calculation. Optical gain spectrum in the QW-heterostructure under uniaxial strain along [110] for different polarizations of light is calculated. For a charge carrier injection of 5 × 10 12 /cm 2 the optical gain is ∼1600/cm under input z-polarization, ∼14500/cm under x-polarization and ∼15700/cm under y-polarization without external uniaxial strain applied. A significant improvement in optical gain is observed under uniaxial strain along [110] direction under different input polarizations. Keeping in views its utilization in optoelectronics due its very high optical gain in near-infra-red region in x- or y-polarization mode, such structure can be considered as a novel structure. [ABSTRACT FROM AUTHOR]

In this paper, the impact of physical parameter variations on the electrical characteristics of III-V TFETs is investigated. The study is performed on the operations of two optimized ultra-thin 20 nm double-gate transistors. The two device structures are InAs homojunction TFET and InAs-GaAs 0.1 Sb 0.9 heterojunction TFET. The operation parameters are the ON-current, OFF-current, and threshold voltage. The investigation is performed at the device level, using a device simulator and the Monte-Carlo simulation approach is exploited to extract the distribution of electrical parameters in the presence of the process variation. The results reveal that the operation of the transistor is more sensitive to the doping of the source and gate work function compared to other physical parameters. Furthermore, the heterojunction TFETs show less sensitivity to physical parameter variations compared to the homojunction ones. [ABSTRACT FROM AUTHOR]

Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V1-yVy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux. [ABSTRACT FROM AUTHOR]

This review paper summarizes some of results achieved during last years of our quantum dot (QD) research. We show that the QD shape (aspect ratio and elongation) significantly influences the QD photoluminescence (PL) spectrum. Magnetophotoluminescence can be used for determination of the anisotropy of QDs. While the calculated shifts in magnetic field of the energies of higher radiative transitions are found to be sensitive to the lateral elongation, the shift of the lowest transition is determined mainly by the exciton effective mass. This behavior can be used for determining both the effective mass and the elongation fairly reliably from the magnetophotoluminescence spectra displaying at least two resolved bands. Lateral shape of InAs/GaAs QDs in vertically correlated structures was also studied. We found the ways to control the QD elongation and consequently the energy difference between PL transitions by adjusting properly the spacer layer thickness. The main goal was to redshift QD PL emission towards telecommunication wavelengths of Metal Organic Vapor Phase Epitaxy prepared InAs/GaAs QDs using InGaAs or GaAsSb covering strain reducing layer (SRL). Our results proved that GaAsSb SRL improves the QD PL properties and the type I or type II band alignment can be controlled by both, GaAsSb composition and QD size. Maintaining the type I heterostructure is important for high luminescence efficiency and emission wavelength stability of QD structure. The simulation of electron structure in InAs QDs covered with GaAsSb SRL and experimental results reveal the importance of increasing QD size for obtaining a longer wavelength PL from the type I heterostructure. The type II structure of InAs/GaAs QDs covered by GaAsSb SRL with Sb content near 30% enabled us to achieve extremely long emission wavelength at 1.8 µm. The high amount of antimony in the SRL causes the preservation of QD size, and increased QD size prolongs the PL wavelength. The type II heterostructures with ground state electrons confined in InAs QDs and ground state holes in GaAsSb SRL have a strong potential in detector and solar cell applications as is demonstrated by photocurrent measurement. The dependence of built in electric field on QD PL properties is presented since this knowledge is necessary for application of QDs in different kind of electronic structures. We have experimentally demonstrated that the type I/type II transition of band structure of InAs QD with GaAsSb SRL does not depend only on the composition of the SRL, but also on other structure parameters, like QD size or intensity of electric field. [ABSTRACT FROM AUTHOR]

A unique direct parameter extraction method for the small-signal equivalent-circuit model of InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) is presented. S-parameters measured at cut-off bias are used, at first, to extract the distribution factor X0 for the base-collector capacitance at zero collector current and the collector-to-emitter overlap capacitance Cceo present in InP DHBT devices. Low-frequency S-parameters measured at normal bias conditions then allows the extraction of the external access resistances Rbx, Re, and Rcx as well as the intrinsic HBT elements of the device. The terminal inductances of the device are extracted from high frequency S-parameters by employing the intrinsic HBT elements extracted at low-frequency. Compared to other published direct parameter extraction techniques the proposed method is developed specifically for III-V based HBTs and avoids S-parameters measured at the critical open-collector bias condition. The method is applied to an 1.5~\mum emitter width InP/GaAsSb/InP DHBT device and leads to excellent prediction of the measured S-parameters in the 250 MHz – 65 GHz frequency range. [ABSTRACT FROM AUTHOR]

An impedance-matched voltage sensitivity ( \beta \it v,{\textrm {opt}} ) of 20400 V/W at 94 GHz was achieved at zero bias and room temperature using heterojunction backward diodes that were based on a p+-GaAsSb/i-InAlAs/n-InGaAs that was lattice matched to an InP substrate. Doping concentrations in the diodes were adjusted to optimize the sensitivity and its nonlinear characteristic. The proper donor doping concentration in n-InGaAs to increase its sensitivity was determined to be 1\times 10^18 cm ^-3 . Meanwhile, the proper acceptor doping concentration in a p-GaAsSb layer was 5 \times 10^18 cm ^-3 to achieve a large nonlinearity as a curvature coefficient ( $\gamma $ ) of -49.4~\text{V}^{-1} , which exceeded that of ideal Schottky diode. The dependence of doping concentration on noise performance was also considered. The lattice-matched GaAsSb-based backward diodes are applicable in millimeter wave detectors and mixers. [ABSTRACT FROM AUTHOR]