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The article investigates the effect of rapid thermal annealing of ternary GaAs1–xNx/GaAs solid solutions on the distribution of nitrogen atoms in the crystal lattice. The samples are studied by photoluminescence spectroscopy and high-resolution X-ray diffractometry. Due to the size and electronegativity mismatch of nitrogen and arsenic atoms, nitrogen is incorporated unevenly into the GaAs crystal lattice. Options of the nitrogen atoms arrangement in the GaAs crystal lattice before and after rapid thermal annealing are shown. [ABSTRACT FROM AUTHOR]

A systematic study of spin‐dependent recombination (SDR) under steady‐state optical pumping conditions as a function of nitrogen content, x, in dilute nitride alloys of the form GaAs1−xNx is reported. Use of high‐excitation power densities up to 107 W cm−2 allows measurement of the full SDR versus power curves, even at relatively high nitrogen contents of x = 0.039. Alloy contents for 0.022≤x≤0.039 are determined within δx = ±0.005 by fitting the photoluminescence (PL) spectra using a Roosbroeck–Shockley relation, and values consistent with those obtained by studying the intensity of the GaN‐like LO2 Raman mode are found. PL intensity increases by a factor known as the SDR ratio when switching from linearly to circularly polarized pump excitation. This factor reaches 5 for x = 0.022 and decreases with increasing x, falling to 1.5 for x = 0.039. Moreover, the excitation power required for maximum SDR increases with increasing x, varying from 0.6 mW for x = 0.022 to 15 mW for x = 0.039. These observations indicate an increase in the density of electronically active defects with increasing nitrogen content, both responsible for the SDR and other, standard Shockley–Read–Hall centers. The result demonstrates the importance of including nonspin‐dependent recombination channels in a complete model of SDR. [ABSTRACT FROM AUTHOR]

• Ga(N,As) and Ga(As,Bi) based type-II structures for long wavelength emission on GaAs substrates. • MOVPE grown samples investigated by photoluminescence spectroscopy, high-resolution X-ray diffraction, atomic force microscopy and scanning transmission electron microscopy. • Impact of different interface configurations: Ga(N,As) on Ga(As,Bi), Ga(As,Bi) on Ga(N,As) and with a GaAs interlayer. • Scanning transmission electron microscopy shows enhanced segregation if Ga(As,Bi) is grown on Ga(N,As) instead of GaAs. The type-II band alignment of particular III/V heterostructures is a promising route towards achieving certain wavelengths on specific substrates, which would not be possible with type-I structures. One example is telecommunication lasers on GaAs substrates. This study reports on the progress in combining dilute nitrides and dilute bismides in W-type hetero structures to improve the luminescence intensity, which is a fundamental prerequisite for future incorporation in a laser structure. Increasing the emission wavelength of these structures is challenging and the interface formation is critical, especially as two metastable materials are combined. Here, we investigate the impact of different interface configurations by growing Ga(N,As)/Ga(As,Bi) and Ga(As,Bi)/Ga(N,As) type-II structures. We employ metal–organic vapor phase epitaxy (MOVPE) to grow Ga(N,As) and Ga(As,Bi) layers and investigate the effects of interlayer thicknesses on the structural and optical properties of the hetero structures. The results indicate that − while the introduction of a GaAs interlayer can affect the direct and indirect transitions intensities − it does not significantly improve the interface quality. However, this is strongly influenced by the order in which the materials are grown. The growth of Ga(N,As) on Ga(As,Bi) shows no peculiarities, while the type II transition energy is shifted to lower energies when Ga(As,Bi) is grown on Ga(N,As). High-resolution X-ray diffraction (HR-XRD), photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the samples. [ABSTRACT FROM AUTHOR]

This work presents an investigation of the fully strained GaAsN/GaAs heterostructures obtained by atmospheric pressure metalorganic vapor phase epitaxy, focusing on the analysis of the strain generated in the GaAsN epilayers and its correlation with the formation of split interstitial complexes (N-As)As. We analyzed strained GaAsN epilayers with nitrogen contents and thicknesses varying from 0.93 to 1.81% and 65 to 130 nm, respectively. The composition and thickness were determined by high resolution X-ray diffraction, and the strain was determined by Raman spectroscopy, while the N-bonding configurations were determined by X-ray photoelectron spectroscopy. We found that the strain generated in the GaAsN epilayers is mainly caused by a lattice mismatch with the GaAs substrate. This macroscopic strain is independent of the amount of (N-As)As interstitial defects, while the local strain, induced by an alloying effect, tends to decrease with an increasing ratio of (N-As)As interstitial defects to substitutional nitrogen atoms incorporated into an arsenic sublattice—NAs. Here, we show experimentally, for the first time, a correlation between the strain in the GaAsN epilayers, caused by an alloying effect determined by Raman spectroscopy, and the (N-As)As/NAs ratio estimated by the XPS method. We found out that the (N-As)As interstitials compensate the local strain resulting from the presence of N in the GaAs matrix, if their amount does not exceed ~65% of the substitutional introduced nitrogen NAs. [ABSTRACT FROM AUTHOR]

Owing to their ability to generate non‐classical light states, quantum dots (QDs) are very promising candidates for the large‐scale implementation of quantum information technologies. However, the high photon collection efficiency demanded by these technologies may be impossible to reach for "standalone" semiconductor QDs, embedded in a high‐refractive index medium. In this work a novel laser writing technique is presented, enabling the direct fabrication of a QD self‐aligned—with a precision of ±30 nm—to a dielectric microsphere. The presence of the microsphere leads to an enhancement of the QD luminescence collection by a factor 7.3 ± 0.7 when an objective with 0.7 numerical aperture is employed. This technique exploits the possibility of breaking the N−H bonds in GaAs1−xNx:H by a laser light, obtaining a lower‐bandgap material, GaAs1−xNx. The microsphere, deposited on top of a GaAs1−xNx:H/GaAs quantum well, is used to generate a photonic nanojet, which removes hydrogen exactly below the microsphere, creating a GaAs1−xNx QD at a predefined distance from the sample surface. Second‐order autocorrelation measurements confirm the ability of the QDs obtained with this technique to emit single photons. [ABSTRACT FROM AUTHOR]

The degradation of InGaAsN p-i-n subcell under 1-MeV electron irradiation was studied by characterizing solar cells and dilute nitride bulk layers before and after irradiation. Cells are measured to retain more than 94% of their original photocurrent after 1015 cm−2, 1-MeV electron irradiation. Moreover, no significant degradation of the optoelectronic properties is observed after irradiation. [ABSTRACT FROM AUTHOR]

The inherent ability of plasmonic bowtie nanoapertures (NAs) to localize the electromagnetic field at a subwavelength scale was exploited to engineer the H removal process in dilute nitrides at the nanometer level. Dilute nitride semiconductor alloys (e.g. GaAsN with a small percentage of nitrogen) are characterized by peculiar optoelectronic properties and, most importantly, by an even more peculiar response to hydrogen incorporation. In this class of materials, it is indeed possible to tune post-growth the alloy bandgap energy by a controlled incorporation of hydrogen atoms. The formation of N-H complexes neutralizes all the effects N has on the host matrix, among which is the strong narrowing of bandgap energy. In the present work, bowtie NAs resonant to the N-H complex dissociation energy were numerically modeled by finite element method simulations, realized by a lithographic approach, and characterized by scanning probe microscopy and resonant scattering spectroscopies. The conditions to get the maximum field enhancement at a specific position below the metal/semiconductor interface, namely at the dilute nitride quantum well position, were identified, demonstrating the ability to achieve a plasmon-assisted spatially selective hydrogen removal in a GaAsN/GaAs quantum well sample. Hydrogen removal through bowtie NAs turns out to be way more efficient (approximately two orders of magnitude) than through the plain surface, thus indicating that bandgap engineering through plasmonic nanostructures can be optimized for future efficient realization of site-controlled single-photon emitters and for their deterministic integration in plasmonic devices.

We report on the progress in developing lattice‐matched GaAs‐based solar cells with focus on developing AlGaInP, AlGaAs, and GaInNAsSb materials, aiming at achieving a wide spectral coverage, that is, 0.7–2.2 eV. To this end, we first benchmark the performance of an upright four‐junction GaInP/GaAs/GaInNAsSb/GaInNAsSb solar cells grown by molecular beam epitaxy on p‐GaAs substrates with bandgaps of 1.88, 1.42, 1.17, and 0.93 eV, respectively. The four‐junction cell exhibited an efficiency of ~39% at 560‐sun illumination while showing good electrical performance even up to 1000 suns. As a first step to further improve the efficiency toward 50% level, we demonstrate AlGaInP (>2 eV) and GaInNAsSb (<0.8 eV) subcells. We prove that AlGaInP cells with 0.1 Al composition would exhibit current‐matching condition when being incorporated in a five‐junction architecture together with two GaInNAsSb bottom and AlGaAs top junctions. Furthermore, current matching required for a six‐junction tandem architecture is achieved for an Al composition of 0.26. Overall, the results open a practical path toward fabrication of lattice‐matched solar cells with more than four junctions. [ABSTRACT FROM AUTHOR]

Vertically grown nanowires (NWs) are a research interest in optoelectronics and photovoltaic applications due to their high surface to volume ratio and good light trapping capabilities. This study presents the effects of process and design parameters on self-catalyzed GaAsSbN NWs grown by plasma-assisted molecular beam epitaxy on patterned silicon substrates using electron beam lithography. Vertical alignment of the patterned NWs examined via scanning electron microscopy show the sensitivity of patterned NW growth to the parameters of NW diameter, pitch, dose time, etching techniques and growth plan. Diameters range from 90 nm to 250 nm. Pitch lengths of 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, and 1200 nm were examined. Dry etching of the oxide layer of the silicon substrate and PMMA coating is performed using reactive ion etching (RIE) for 20 s and 120 s respectively. Comparisons of different HF etch durations performed pre and post PMMA removal are presented. Additionally, the report of an observed surfactant effect in dilute nitride GaAsSbN NWs in comparison to non-nitride GaAsSb is presented. Optimizations to patterning, RIE, and HF etching are presented to obtain higher vertical yield of patterned GaAsSbN NWs, achieving ∼80% of the expected NW µ m 2 . Room temperature and 4 K photoluminescence results show the effect of nitride incorporation for further bandgap tuning, and patterned pitch on the optical characteristics of the NWs which gives insights to the compositional homogeneity for NWs grown at each pitch length., (© 2024 IOP Publishing Ltd.)

• Tandem J-V characteristics reveal tunnel junction failure. • Tunnel junction properties different when grown separately that in tandem device. • Insufficient doping and thermal load as a potential factors responsible for tunnel junction degradation. From tandem solar cell we expect a wide absorption range due to different bandgaps of the subcells, higher open circuit voltage V oc and finally better photo conversion efficiency η than single junction solar cell. The main drawback of it is a current limitation i.e. the short circuit current J sc of whole structure is equal to smaller J sc of both subcells. However, even two subcells with very good photovoltaic performance do not guarantee the correct operation of tandem solar cell. The tunnel junction plays a crucial role on tandem devices as it has to provide low loss electrical and optical connection between top and bottom subcells. Within this paper we present two subcells: top GaAs based, bottom InGaAsN based with good photovoltaic performance and InGaAs tunnel diode used for InGaAsN/GaAs tandem solar cell construction. We compare reference devices with monolithic tandem cell and conclude about tunnel junction failure based on both dark and illuminated J-V characteristics of the InGaAsN/GaAs final device. Based on detailed analysis of tandem performance we propose two most likely effects responsible for tunnel junction induced deterioration of tandem solar cell performance. [ABSTRACT FROM AUTHOR]

The inhomogeneities of multicomponent semiconductor alloys, as well as phase segregation, can be utilized for enhancement of photodetector absorption properties and thus its efficiency. In this paper, the influence of external electric field on the probability of light absorption in the GaInNAs quantum well is discussed. Both phenomenon: indium and nitrogen composition gradient as well as step-like quantum well are applied to design the QW with compensation of the Quantum-Confined Stark Effect (QCSE) Parasitic effect of QCSE results from decrease of the wave functions overlapping in the QWs placed in reverse biased junction, which finally decrease the efficiency of the photodetector.

Basic knowledge about the factors and mechanisms affecting the performance of solar cells and their identification is essential when thinking of future improvements to the device. Within this paper, we investigated the current transport mechanism in GaAsN p-i-n solar cells grown with atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE). We examined the electro-optical and structural properties of a GaAsN solar cell epitaxial structure and correlated the results with temperature-dependent current-voltage measurements and deep level transient spectroscopy findings. The analysis of J-V-T measurements carried out in a wide temperature range allows for the determination of the dominant current transport mechanism in a GaAsN-based solar cell device and assign it a nitrogen interstitial defect, the presence of which was confirmed by DLTFS investigation.

Abstract We demonstrate single junction GaInNAsSb solar cells with high nitrogen content, i.e. in the range of 5–8%, and bandgap energies close to 0.7 eV grown by molecular beam epitaxy. A good crystalline quality is demonstrated for the entire range of N concentrations. An average external quantum efficiency of 0.45 is demonstrated for GaInNAsSb solar cell with 6.2% N exhibiting a bandgap of 0.78 eV (no antireflection coatings has been applied). The internal quantum efficiency for the cell is 0.65 at E g + 0.2 eV. The solar cells exhibited bandgap-voltage offsets between 0.55 V (for N = 5.3%) and 0.66 V (for N = 7.9%). When used in a six-junction solar cell architecture under AM1.5D illumination, the estimated short-circuit current density corresponding to the 0.78 eV cell is 8.2 mA/cm2. Furthermore, using the parameters obtained for the GaInNAsSb junction with 6.2% N, we have estimated that such six-junction solar cell architecture could realistically attain an efficiency of over 50% at 1000 suns concentration. Highlights • GaInNAsSb/GaAs bulk heterostructures with high N compositions of 6–8% demonstrated. • Demonstration of highest EQE to date for 0.78 eV GaInNAsSb solar cell. • Simulation of a 6-junction solar cell shows potential for more than 50% efficiency. [ABSTRACT FROM AUTHOR]

Degradation analysis of a quantum well-dilute nitride based multi-junction solar cell is presented using a 2D numerical device simulator: APSYS. By taking carrier removal effects into consideration, the proposed device exhibits strong electric field uniformity within the intrinsic region of the p-i-n middle cell. The electron traps are defined in the top InGaP and bottom InGaAsN base region considering 1 MeV electron irradiation in geostationary orbits. Considering thermionic emission, tunneling and SRH lifetime an effective lifetime value of 16.7 ps is considered in the middle MQW region. A record efficiency value of 38% and 44% is obtained at 1-sun and 500-sun AM0 spectrum respectively. The same efficiency value dropped by 4% by introducing a realistic SRV (1 × 104 cm s−1) and trap concentration values (1 × 1016 cm−3). Finally, we illustrate the influence of traps and lifetime on overall cell J sc , V oc , η, and power density. [ABSTRACT FROM AUTHOR]

Monolithic four‐junction solar cells incorporating two dilute nitride (GaInNAsSb) bottom junctions are reported. The dilute nitride junctions have band gaps of 0.9 and 1.2 eV, while the top junctions have band gaps of 1.4 and 1.9 eV. By using experimental‐based parametrization, it was estimated that the four‐junction solar cell could theoretically exhibit efficiency levels of 34.7% at one sun, 43.2% at 100 suns, and 46.4% at 1000 suns for AM1.5D illumination. The most challenging subcell in terms of fabrication is the GaInNAsSb bottom junction with 0.9 eV band gap. For this subcell, a background doping level down to 5 × 1014 cm−3 and a high charge carrier lifetime up to 2 to 4 nanoseconds are reported, which reflects high values for current and voltage. An experimental AlGaAs/GaAs/GaInNAsSb/GaInNAsSb solar cell structure was fabricated by molecular beam epitaxy. At one‐sun AM1.5D illumination, the experimental cell exhibited an efficiency of 25%, an average quantum efficiency of 91%, and an open circuit voltage, which is about 87% of the estimated potential. The cell exhibited maximum efficiency of 37% at 100‐sun concentration. Lattice‐matched AlGaAs/GaAs/GaInNAsSb/GaInNAsSb solar cell, incorporating 1.2 and 0.9 eV band gap dilute nitride bottom junctions, is reported. The cell exhibited up to 37% conversion efficiency at 100 suns and high average quantum efficiency of 91%. Theoretically, estimation based on realistic parametrization indicates that the cell could achieve 34%, 43%, and 46% at 1, 100, and 1000 suns, respectively. [ABSTRACT FROM AUTHOR]

The development of low bandgap GaAsNBi solar cells grown using MBE is reported. The devices include a pin heterostructure with GaAsNBi as the i-layer. The substrate rotation is stopped during epitaxy of the GaAsNBi layer (stationary growth), resulting in a continuous variation in the source fluxes over the wafer, enabling the investigation of a wide range of growth conditions in a single growth run. In particular, we investigate the photovoltaic properties as a function of the As/Ga flux ratio around the critical stoichiometric value. For slightly below stoichiometric As/Ga, the lattice mismatch and bandgap energy are minimized to 8 × 10-4 and 0.86 eV, respectively, while the crystal quality remains good. Increasing As/Ga over the stoichiometric ratio leads to a rapid increase in the tensile mismatch and bandgap energy, likely due to reduction in Bi incorporation. Despite a slightly higher open-circuit voltage offset at high As/Ga, this also leads to an clear increase in the external quantum efficiency and short-circuit current, suggesting significant differences in the carrier collection efficiencies. The results demonstrate the importance of the As/Ga flux ratio in controlling the solar cell performance, and the viability of GaAsNBi as a candidate for a low bandgap subjunction in multijunction solar cells. • Low-bandgap pin-GaAsNBi solar cells. • Use of stationary MBE growth to optimize performance. • As/Ga ratio has a drastic effect on the material properties and photovoltaic operation. • Demonstration of photovoltaic operation at 0.86 eV. [ABSTRACT FROM AUTHOR]

Progress in monolithic integration of III-V semiconductor heterostructures on silicon promotes the development of silicon-based integrated optoelectronics. Here, we report on the fabrication of dual-functional light-emitting and photo-detecting heterostructures based on aluminum-free quaternary dilute nitride alloys of GaAsPN, epitaxially grown on silicon wafers, operating in the red part of the visible spectrum. The use of indirect band gap GaP cladding layers minimizes light absorption and simplify fabrication technology. The low-temperature grown GaP/AlGaP nucleation layer has been employed to achieve antiphase domain-free growth of GaP on Si (001). Quaternary GaAsPN alloy layers with bandgap values, ranging from 1.94 to 1.83 eV, were grown by plasma-assisted molecular beam epitaxy at a high temperature of 540 °C, which ensures high crystallinity. The influence of growth conditions on the GaAsPN alloy composition, structure and optoelectronic properties is discussed. The fabricated p-i-n mesa diodes demonstrate low leakage currents and both photocurrent response with an external quantum efficiency in the range of 30–42% and bright red interband electroluminescence at room temperature. [Display omitted] • GaAsPN on Si pin heterostructures show light emission and detection functionality. • High temperature PA-MBE growth provides structural perfection and E g tunability. • Simple two-step procedure provides antiphase domain-free III-V/Si heteroepitaxy. • Bright red electroluminescence at 300 K and low leakage current demonstrated. • Photovoltaic external quantum efficiency of 42% achieved. [ABSTRACT FROM AUTHOR]

Controlled growth of heterostructured nanowires and mechanisms of their formation have been actively studied during the last decades due to perspectives of their implementation. Here, we report on the self-catalyzed growth of axially heterostructured GaPN/GaP nanowires on Si(111) by plasma-assisted molecular beam epitaxy. Nanowire composition and structural properties were examined by means of Raman microspectroscopy and transmission electron microscopy. To study the optical properties of the synthesized nanoheterostructures, the nanowire array was embedded into the silicone rubber membrane and further released from the growth substrate. The reported approach allows us to study the nanowire optical properties avoiding the response from the parasitically grown island layer. Photoluminescence and Raman studies reveal different nitrogen content in nanowires and parasitic island layer. The effect is discussed in terms of the difference in vapor solid and vapor liquid solid growth mechanisms. Photoluminescence studies at low temperature (5K) demonstrate the transition to the quasi-direct gap in the nanowires typical for diluted nitrides with low N-content. The bright room temperature photoluminescent response demonstrates the potential application of nanowire/polymer matrix in flexible optoelectronic devices.

Highlights • InGaAsN/AlGaAs QWIPs for e-SWIR. • CBO values reaching up to ∼1 eV with GaAs technology. • Room temperature photocurrent response that spans between 1.1 and 2.2 μm. • Room temperature responsivity of 15 and 1 A/W for 1.65 μm and 2 μm, respectively. • Corresponding detectivity values of ∼1010 and ∼5 × 108 cm·Hz1/2/W at 1.65 μm and 2.0 μm, respectively. Potential detectivity values as high as ∼2 × 1012 and ∼1 × 1011 cm·Hz1/2/W for ∼1.65 μm and 2.0 μm, respectively can be achieved. Abstract We propose and demonstrate a novel concept to address high-performance, extended short wavelength (e-SWIR) photodetectors. Our approach is based on shifting the well-developed GaAs quantum-well infrared photodetector (QWIP) technology to e-SWIR wavelengths. In order to increase the available conduction band offsets (CBOs), we suggest incorporating nitrogen (N) atoms into the quantum well material. The incorporation of N atoms into III-Vs results in dilute-nitride highly mismatched alloys with lower bandgaps and higher CBOs. In our work, we demonstrate CBO values reaching up to ∼1 eV in InGaAsN/AlGaAs QWIPs. This large CBO makes these structures suitable for e-SWIR detection. The large CBO reduces the dark current dramatically and allows efficient detection at room temperature. In our study, we devised two similar InGaAsN/AlGaAs QWIP devices with twofold, 1% and 2% N composition. Based on the measured dark current data, we extracted activation energy barriers of 780 meV and 580 meV for the 1% and 2% N devices, respectively. The dark current and photocurrent spectral response behave in correlation to the change in the barriers' height. The photocurrent response of the 1% N device peaks at ∼2.25 μm and spans at a spectral range between 1.3 and 2.95 μm. The photocurrent response of the 2% N device is blue shifted to ∼1.42 μm and spans at a spectral range between 1.1 and 2.2 μm. The 2% N device exhibits lower dark currents and a strong photoresponse at room temperature, whereas the 1% N device exhibits a clear response only at temperatures below 150 K. The detection mechanism in the InGaAsN/AlGaAs QWIP devices is based on optical excitation of carriers from the quantum wells into highly-localized nitrogen-related E+ defect-like states located energetically above the conduction band edge. For this reason, the photoresponse is insensitive to the radiation polarization and exhibits low absorption efficiency on the order of 0.15% per quantum well. However, at the same time, the responsivity and photocurrent gain are very high due to the long lifetime of the highly localized excited states. The peak responsivity of the 2% N device is ∼70 A/W at room temperature. Significant responsivity is also available at the response tail at longer wavelengths, i.e., ∼15 and 1 A/W for 1.65 μm—the peak wavelength of the night glow emission and 2 μm—at the e-SWIR wavelengths, respectively. Corresponding detectivity values are ∼1010 and ∼5 × 108 cm·Hz1/2/W at 1.65 μm and 2.0 μm, respectively. These values are similar to those of other developing technologies. In-reach potential detectivity is estimated based on the measured data and can arrive easily to values as high as ∼2 × 1012 and ∼1 × 1011 cm·Hz1/2/W for ∼1.65 μm and 2.0 μm, respectively. The presented characteristics and potential performance indicate that InGaAsN/AlGaAs quantum wells are most suitable for efficient e-SWIR photodetection. [ABSTRACT FROM AUTHOR]

We present an experimental study of GaAsSbN layers with thickness around 1μm, grown by liquid-phase epitaxy on n-type GaAs substrates. The samples are studied by surface photovoltage (SPV) spectroscopy at room temperature. The analysis of the SPV spectra has provided information about the optical absorption and the photocarrier transport in the samples. In particular, a red shift of the energy bandgap with respect to GaAs is found. Its values are larger as compared to our previous data obtained in InGaAsN layers, grown by the same technique. [ABSTRACT FROM AUTHOR]

The effects of ex situ annealing in N ambient and in situ annealing in As ambient on GaNSbAs/GaAs structures grown by molecular beam epitaxy were investigated by low temperature cross-sectional cathodoluminescence (CL). The amount and distribution of Sb was measured by energy dispersive spectroscopy (EDS). The cross-sectional CL analysis of all samples reveals a shift of the near band edge (NBE) emission along the growth axis, presumably associated with a non-uniform incorporation of Sb during the growth process, in agreement with the Sb distribution measured by EDS in the as-grown sample. The NBE emission in the annealed samples presents a redshift with respect to the as-grown sample. This effect might be explained by a redistribution/activation of N in the GaNSbAs lattice since the Sb distribution measured by EDS does not reveal significant changes, within the error margin, with respect to the as-grown sample. The in situ annealed in the As overpressure sample shows the best properties for solar cells applications, i.e., a NBE peak position close to 1.0 eV and the lowest full width at half maximum of this emission. [ABSTRACT FROM AUTHOR]

This work presents the results of X-ray photoelectron spectroscopy studies on the bonding N configuration in InGaAsN epilayers grown by atmospheric pressure metal organic vapour phase epitaxy. Growth temperature has been tuned in order to obtain both, relaxed and strained layers. The studies were concentrated on analysing the influence of the growth temperature, post growth thermal annealing process and surface quality on the formation of Ga-N and In-N bonds as well as N-related defects. The contamination of InGaAsN films by growth precursor residues and oxides has also been addressed. The growth temperature stands out as a decisive factor boosting In-N bonds formation, while the thermal annealing seems to affect the N-related defects density in the layers. [ABSTRACT FROM AUTHOR]

A theoretical study of electronic structures and optical properties of GaInNAs/GaAs quantum wells has been performed. The inhomogeneous distributions of indium and nitrogen atoms along the growth direction were discussed as the main factors having significant impact on the QWs absorption efficiency. The study was performed by applying the band anticrossing model combined with the envelope function formalism and based on the material parameters which can be found in the literature. Indeed, the electronic band structure of 15 nm thick uniform Ga0.7In0.3N0.02As0.98/GaAs QW was computed together with electronic structures of several types of inhomogeneous QWs, with the same total content of In and N atoms. It was found that presented inhomogeneities lead to significant quantum wells potential modifications and thus to spatial separation of the electrons and holes wave functions. On the other hand, these changes have a significant impact on the absorption coefficient behavior. This influence has been studied on the basis of simulated photoreflectance spectra, which probe the absorption transitions between QW energy subbands. The electronic structure of inhomogeneous QWs under the influence of electric field has also been studied. Two different senses of electric field vector (of p-i-n and n-i-p junctions) have been considered and thus, the improvement of such types of QWs-photodetectors based on inhomogeneous GaInNAs QWs has been proposed. [ABSTRACT FROM AUTHOR]

Using first-principles total energy calculations, we have studied the structural, mechanical and electronic properties of GaAs 1- x N x ternary semiconductor alloys with the zinc-blende crystal structure over the whole nitrogen concentration range (with x from 0 to 1) within density functional theory (DFT) framework. To obtain the ideal band gap, we employ the semi-empirical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U). The calculated results illustrate the varying lattice constants and band gap in GaAs 1- x N x alloys as functions of the nitrogen concentration x . According to the pressure dependence of the lattice constants and volume, the higher N concentration alloy exhibits the better anti-compressibility. In addition, an increasing band gap is predicted under 20 GPa pressure for GaAs 1- x N x alloys. [ABSTRACT FROM AUTHOR]

We report on a novel lithographic approach for the fabrication of integrated quantum dot (QD)-photonic crystal (PhC) nanocavity systems. We exploit unique hydrogen's ability to tailor the band gap energy of dilute nitride semiconductors to fabricate isolated site-controlled QDs via a spatially selective hydrogenation at the nanometer-scale. A deterministic integration of the realized site-controlled QDs with PhC nanocavities is provided by the inherent realignment precision (~ 20 nm) of the electron beam lithography system used for the fabrication of both QDs and PhC cavities. A detailed description of the fabrication steps leading to the realization of integrated QD-PhC cavity systems is provided, together with the experimental evidence of a weak coupling effect between the single-photon emitter and the PhC cavity. [ABSTRACT FROM AUTHOR]

The effects of 7 MeV electron irradiation at very high doses of 2 × 10 17 and 1.5 × 10 18 electrons / cm 2 and subsequent rapid thermal annealing on photoluminescence from a strain-compensated GaInAsN/GaAsN/GaAs quantum well structure are investigated. A large additional blueshift of photoluminescence has been observed from the lower-dose irradiated sample as compared to the non-irradiated one when annealed after the irradiation. This additional blueshift will become considerably reduced by an ageing effect, which occurs already at room temperature. The mechanism causing the additional blueshift of photoluminescence and its reduction is qualitatively assigned to metastable complex defects promoted by electron irradiation in the nitrogen containing layers. No such additional blueshift of photoluminescence under the thermal treatment has been observed in the higher-dose irradiated sample. [ABSTRACT FROM AUTHOR]

In this work, InSbN alloys were hetero-eptiaxially grown on GaSb (100) substrate by metal-organic chemical vapor deposition, expecting large nitrogen addition and long cut-off wavelength of the samples simultaneously. Post annealing treatment was carried out to see the effect on the alloy structural and optical properties. Photoluminescence results indicate that the band gap wavelength of the alloys is reduced to 6.3 μm by the N incorporation. Besides, another peak around 8.3 μm could also be detected, and the peak intensity is comparable to the main band emission, which means much for the application in long wavelength devices. The cause of the defect emission was discussed through the analysis of Photoluminescence and X-ray photoelectron spectroscopy measurement results. [ABSTRACT FROM AUTHOR]

In this work authors present the results of structural and optical characterization of the GaInNAs/GaAs MQW structures grown by AP-MOVPE. The growth conditions of quantum well layers were modified in order to counteract the phase segregation within GaInNAs QWs. Profiles of indium and nitrogen contents across the QWs layers were investigated by using HRXRD. The optical properties were investigated by applying photoluminescence spectroscopy. The inhomogeneous composition of the GaInNAs QW layers is considered as a factor suppressing the PL intensity due to change in the electron and holes wave functions distributions and tuning the transition's selection rules. [ABSTRACT FROM AUTHOR]

Charge transfer excitons are studied in double quantum well structures consisting of a (GaIn)As and a Ga(NAs) layer separated by a GaAs film of variable thickness. With decreasing barrier thickness, the gradual change from a spatially direct exciton within the (GaIn)As well to a charge transfer exciton bound across the GaAs spacing layer is observed. The optical spectra are well reproduced by a fully microscopic theory and band structure calculations based on the k · p method using a weak type-I valence band offset of approximately ( 45 ± 40 ) meV at the Ga(NAs)/GaAs interface. [ABSTRACT FROM AUTHOR]

In the presented work the growth and fabrication process of dilute nitride based solar cells were reported. We fabricated three different solar cells to investigate the influence of top contact on their electrical parameters. Test devices were characterized by the means of current–voltage measurements carried out under the sunlight simulator. The obtained I – V results were scrutinized using a single diode equivalent circuit of a solar cell. We employed the Lambert W approach to find the solvable solution of the modified Shockley equation, in order to determine the basic solar cell electrical parameters such as: ideality factor n , series and shunt resistances ( R s and R sh ), saturation current I 0 and photocurrent I ph generated in the solar cell structure. It was found that electrical parameters obtained from the fitting procedure depend on solar cell design. The type of top electrode influences the values of parasitic resistances, open circuit voltage and short circuit current. [ABSTRACT FROM AUTHOR]

The correlation between the As to group III flux ratio and photovoltaic performance of GaIn 0.1 N 0.03 As solar cells fabricated by molecular beam epitaxy is systematically investigated. The results show that flux ratio has a remarkable influence on the formation of defect traps. Furthermore, the formation of defects at different flux ratios is correlating with the variation of the background doping level and the photovoltaic performance. In particular, this study reveals a linear dependency between current generation, dark saturation current, defect densities, photoluminescence peak intensity and the flux ratio. A significant increase in solar cell performance, exhibiting maximum external quantum efficiency of 90%, is obtained when As/group-III ratio is decreased close to the stoichiometric limit. For optimized growth condition, the 1 eV GaIn 0.1 N 0.03 As solar cell exhibits a short circuit current density as high as 17.9 mA/cm 2 calculated from the external quantum efficiency data (AM0 conditions) with 870 nm high-pass filter. This value reflects the potential of the GaInNAs cell for current matching and power generation in high efficiency solar cells incorporating three- or four- junctions. [ABSTRACT FROM AUTHOR]

We correlate the structural properties of aluminium-based dilute nitrides to their electrical properties. The effect of annealing on the carrier density and the mobility is measured on chemical beam epitaxy grown Al0.05Ga0.95N0.005As0.995 alloys. Both parameters increase with the annealing temperature due to the disappearance of N-C and N-H-VGa complexes. After annealing, a mobility of 60 cm2 V−1s−1 for a hole concentration of 1 × 1019 cm−3 are measured, which is similar to the values reported on GaAs with the same carrier concentration. [ABSTRACT FROM AUTHOR]

In this work, the authors present the results of optical characterization of GaAs-based multiple quantum well heterostructures, together with energy band structure analysis. The optical properties were investigated by applying photoluminescence spectroscopy. Structures with GaInNAs, GaInAs and GaNAs multiple quantum wells emitting around 1 μm, grown by atmospheric pressure metalorganic vapor phase epitaxy, were compared in this work. The role of nitrogen in quantum well carriers confinement potential was analysed. The photoluminescence intensities of the samples were correlated with the analysis of energy band structures and the overlaps of the carriers' wave functions. In addition, the main carrier activation energies were estimated based on photoluminescence temperature dependence and the Arrhenius plots analysis. It was deduced that the thermal photoluminescence decay is most probably related to the escape of electrons whereas the holes, independently of the potential well depth, are additionally confined by the local inhomogeneities or by the Coulomb interaction with the confined electrons. [ABSTRACT FROM AUTHOR]

We report study on stacked InAs/GaNAs quantum dots heterostructures with dilute nitride GaInNAs strain mediating layers embedded in GaAs p-i-n solar cell structure. The insertion of GaInNAs strain mediating layers in the vicinity of the strain compensated InAs/GaNAs quantum dots heterostructures enhances their surface density, improves and significantly red shifts their light emission. Embedding a stack of the strain-mediated InAs/GaInNAs/GaNAs quantum dots in the i region of a GaAs p-i-n solar cell leads also to a red shift of the absorption edge of the solar cells and improves the solar cell photogenerated currents at longer wavelengths beyond 1200 nm. [ABSTRACT FROM AUTHOR]

The effects of ex-situ annealing in a N ambient on the properties of GaAs/GaAsSbN/GaAs core-multi-shell nanowires on Si (111) substrate grown by self-catalyzed molecular beam epitaxy (MBE) are reported. As-grown nanowires exhibit band edge emission at ~0.99 eV with a shoulder peak at ~0.85 eV, identified to arise from band tail states. A large red shift of 7 cm and broadened Raman spectra of as-grown nanowires compared to that of non-nitride nanowires confirmed phonon localization at N-induced localized defects. On annealing nanowires to 750 °C, there was no change in the planar defects in the nanowire with respect to the as-grown nanowire; however, vanishing of the photoluminescence (PL) peak corresponding to band tail states along with enhanced band edge PL intensity, recovery of the Raman shift and increase in the Schottky barrier height from 0.1 to 0.4 eV clearly point to the efficient annihilation of point defects in these GaAsSbN nanowires. A significant reduction in the temperature-induced energy shift in the annealed nanowires is attributed to annihilation of band tail states and weak temperature dependence of N-related localized states. The observation of room temperature PL signal in the 1.3 μm region shows that the strategy of adding small amounts of N to GaAsSb is a promising route to realization of efficient nanoscale light emitters with reduced temperature sensitivity in the telecommunication wavelength region. [ABSTRACT FROM AUTHOR]

High performance narrow-bandgap GaInNAsSb solar cells are instrumental for the development of lattice-matched GaAs-based solar cells with more than four junctions. To this end a comprehensive optimization process including the effects of growth temperature, As/III beam equivalent pressure ratio, and Sb flux on the performance of 0.8 eV GaInNAsSb solar cells grown by molecular beam epitaxy is reported. For this, sets of GaInNAsSb p-i-n solar cell structures with 5–6% nitrogen compositions were fabricated, while varying the key growth parameters. The quantum efficiency and current generation increased significantly when the narrow gap materials were grown at elevated growth temperatures, close to phase separation. A further improvement in the current generation was observed by employing lower As/III beam equivalent pressure ratios. The best GaInNAsSb cell exhibited about 94% peak external quantum efficiency and generated a short-circuit current of 17.7 mA/cm2 with AM1.5D (1000 W/m2) illumination at wavelengths above 900 nm without employing a back surface reflector. Our analysis indicates that the best cell is already close to being absorption limited. While the N composition should be kept as low as possible (i.e., ≲5%) to achieve high performance, increasing the Sb flux generally results in improved the material quality, i.e., leading to a slight improvement for the open-circuit voltages and fill factors. In addition, it was found that the phase separation observed at the growth temperature of 480 °C could effectively be inhibited by employing higher Sb fluxes. • Optimized MBE growth for 0.8 eV GaInNAsSb solar junctions with 5–6% N content. • High current obtained using high growth temperatures and lower As pressures. • High peak external quantum efficiency of 94% demonstrated. • Background doping level as low as 1.1 × 1015 cm−3 for GaInNAsSb with 6% N. • Phase separation is suppressed, and power output improved by optimizing Sb flux. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the high-speed data processing capabilities of a GaInNAsSb semiconductor optical amplifier operating at 1.55~\mu \textm . The investigated structure exhibits good thermal characteristics and fast gain dynamics with 10%–90% recovery time of 55 ps. Successful wavelength conversion of 10-Gb/s signals is reported. A maximum power penalty of <2.4 dB for return to zero formatting and of 1.9 dB for nonreturn to zero is demonstrated. [ABSTRACT FROM PUBLISHER]

III/V semiconductors with cubic zinc-blende crystal structure, for example GaAs, GaP or InP, become metastable if atoms with significantly smaller or larger covalent radius than the matrix atoms are alloyed. Examples are the incorporation of Boron, Nitrogen and Bismuth in the above-mentioned materials. The resulting multinary compound semiconductors, like for example (Ga,In)(N,As), Ga(N,As,P) and Ga(As,Bi), are extremely interesting for several novel applications. The growth conditions, however, have to be adopted to the metastability of the material systems. In addition, structure formation can occur which is different from stable materials. This paper summarizes our current knowledge on growth characteristics of several metastable materials. Mainly examples for Metal Organic Vapor Phase Epitaxy (MOVPE) are given. The MOVPE growth characteristics are compared to selected examples using Molecular Beam Epitaxy growth to highlight that the observed growth characteristics are intrinsic for the studied metastable material systems. Furthermore, structural peculiarities of dilute borides, nitrides and bismides occurring during growth as well as in growth interruptions are summarized and correlated to the growth conditions. [ABSTRACT FROM AUTHOR]

This paper delivers an approximation to the complex many body problem of luminescence in semiconductors to the case of mid infrared luminescence of dilute nitrides. The results are compared with recent experimental data for InAsN semiconductors. [ABSTRACT FROM AUTHOR]