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Surface photovoltage (SPV) spectra were measured for GaN 0.014 As 0.986 layers at room temperature and compared with room temperature photoreflectance (PR) and contactless electroreflectance (CER) measurements. Spectral features related to E − and E + transitions were clearly observed in SPV spectra at energies corresponding to PR and CER resonances. In this way it has been shown that SPV spectroscopy is an alternative absorption-like technique to study both the E − and E + transitions in dilute nitrides. The observation of E + transition in SPV spectra means that it is a direct optical transition at the Γ point of GaNAs band structure which can be explained by the band anticrossing interaction between the localized states of N and the extended conduction band states of the GaAs host. [ABSTRACT FROM AUTHOR]

GaInNAs alloys are mostly used as an active part of light sources for long wavelength telecom applications. Beside this, these materials are used as thin quantum wells (QWs), and a need is to grow thick layers of such semiconductor alloys for photodetectors and photovoltaic cells applications. However, structural characterization of the GaInNAs layers is hindered by non-homogeneity of the In and N distributions along the layer. In this work the challenges of the structural characterization of doped thick GaInNAs layers grown by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE) will be presented [ABSTRACT FROM AUTHOR]

Tandem (two p-n junctions connected by tunnel junction) and multijunction solar cells (MJSCs) based on AIIIBV semiconductor compounds and alloys are the most effective photovoltaic devices. Record efficiency of the MJSCs exceeds 44% under concentrated sunlight. Individual subcells connected in series by tunnel junctions are crucial components of these devices. In this paper we present atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE) of InGaAsN based subcell for InGaAsN/GaAs tandem solar cell. The parameters of epitaxial structure (optical and electrical), fabrication process of the test solar cell devices and current-voltage (J-V) characteristics are presented and discussed. [ABSTRACT FROM AUTHOR]

We have investigated the role of the nitrogen content, the growth parameters, and the annealing processes involved in molecular beam epitaxy of GaInNAs solar cells lattice-matched to GaAs. The nitrogen composition was varied between 1% and 5%. The influence of the growth temperature was assessed by performing photoluminescence, atomic force microscopy, X-ray diffraction, reflection high-energy electron diffraction, quantum efficiency and light-biased current–voltage measurements. The growth temperature ensuring the best cell parameters was found to be 440°C. At this temperature we were able to incorporate up to 4% of nitrogen and achieve a good material quality. Further increase of the N composition to 5% led to phase separation. For the lattice matched samples grown within the optimal temperature range, we have identified a clear (1×3) surface reconstruction. Using the optimized growth we have demonstrated a GaInNAs p-i-n solar cell structure containing 4% nitrogen, that exhibited a short-circuit current density as high as 33.8mA/cm2 in respect to effective area illuminated. These measurements have been performed under real sun AM1.5 (~1000W/m2) illumination. [ABSTRACT FROM AUTHOR]

Determination of indium and nitrogen content in InGaAsN quantum wells (QWs) is often based on the analysis of high-resolution X-ray diffraction (HRXRD) measurements. The comparison of diffraction curves of two similar samples, with and without nitrogen, together with an assumption of constant indium incorporation efficiency during the growth of layers with and without nitrogen, may lead to a large deviation in the determined In and N content. The HRXRD curve simulations supported by bandgap determination and calculations seem to be a solution of this problem. Comparison of the results achieved from simulated HRXRD curves with the calculations of all QWs transitions measured by contactless electro-reflectance (CER) can lead to reduction of deviations in composition determination of InGaAsN quantum wells. The proposed algorithm was applied for investigation of InGaAsN QWs grown by atmospheric pressure metalorganic vapor phase epitaxy (APMOVPE). [ABSTRACT FROM AUTHOR]

The effects of growth temperature (410 and 470°C) and subsequent rapid thermal annealing (RTA) on luminescence performance of lattice-matched 1-eV GaInNAs-on-GaAs epilayers, grown by molecular beam epitaxy under constant fluxes, has been studied experimentally by 9-K photoluminescence (PL) and 300-K photoreflectance (PR) spectroscopy. The near band edge PL has been found to noticeably decrease and red-shift as the growth temperature (T gr) is reduced from 470 to 410°C. This red-shift is the consequence of a reduction in the alloy band gap with decreasing T gr, as confirmed by PR. An N-related broad PL band, whose intensity remarkably enhances with increasing T gr, has been detected at longer wavelengths in the 9-K PL's. Post-growth RTA (1min at 800°C) significantly enhanced the near band edge PL but it did so at the expense of a PL blue-shift: the more the PL enhancement and blue-shift the lower the T gr. This annealing-induced blue-shift is due to In–N bonds formation, whose magnitude enhanced as the T gr is decreased. The broad PL band also enhanced upon the RTA, but the ratio between its intensity and the intensity of the near band edge PL reduced, especially for the sample grown at 410°C. 7-MeV electron irradiation to the dose of around 1015 cm−2 applied prior to annealing considerably reduced the broad PL band upon annealing. [ABSTRACT FROM AUTHOR]

Abstract: We adapted the atomic layer epitaxy (ALE) technique to grow GaAsN thin films. The effects of the gas flow sequences used on the self-limiting mechanism (SLM), the N incorporation ratios, and the concentrations of residual impurities were investigated. A pulse of the N precursor (monomethylhydrazine) was added after that of the Ga precursor (trimethylgallium) or the As (trisdimethylaminoarsenic) precursor, which were part of the conventional sequence used for the growth of GaAs films via ALE. If it was noticed that the SLM was in effect, the N precursor was supplied on the Ga- or As-terminated surface (the corresponding sequences and their resulting films are labeled as On-Ga and On-As, respectively). The On-As film exhibited rough surfaces, nonuniform N concentration, and disordered lattices owing to defects. On the other hand, in the case of the On-Ga sequence, GaAsN films with high-quality crystals were grown with the SLM in effect and the concentration of N being a few percent. The concentrations of the residual impurities (C and H) in the On-Ga film were low. This demonstrated that the On-Ga sequence was effective for growing GaAsN thin films on precisely controlled surfaces using the ALE technique. [Copyright &y& Elsevier]

Abstract: GaP0.98N0.02 layers having a thickness from 75nm to 600nm are grown on GaP substrates by metalorganic vapor phase epitaxy. Back-reflection X-ray topographs made with a synchrotron radiation of the thick GaP0.98N0.02 layers reveal images of misfit dislocations. The critical thickness of the grown GaP0.98N0.02 layer on GaP substrate is evaluated from the topographs to be about 200nm. The strain relaxation is also observed from high resolution X-ray diffraction curves. X-ray diffraction curves and atomic force microscopy studies indicate that the GaP0.98N0.02 layers with thickness smaller than 200nm possess a very good crystal quality, an atomically smooth surface with a roughness less than 0.3nm and a well-defined interface without misfit dislocations between the layer and the substrate. [Copyright &y& Elsevier]

Abstract: We have investigated the influence of 7-MeV electron irradiation (1.2×1015 and 1.8×1016 electrons/cm−2 doses) and subsequent rapid thermal annealing (RTA) on luminescence efficiency of nearly lattice-matched 1-eV GaInNAs-on-GaAs thin epilayers, grown by molecular beam epitaxy. The study has been done by means of 9K photoluminescence (PL) in conjunction with 300K photoreflectance (PR) spectroscopy and x-ray diffraction (XRD) measurements. An enhancement in PL has been found for the lower dose whereas a drastic deterioration in PL has been seen for the higher dose. When rapid thermally annealed at 800°C for 1min an enhancement in PL has been observed, noticeably for the sample irradiated at a higher dose, as compared to the reference non-irradiated sample. The irradiation-promoted enhancement in PL upon annealing has been accompanied by a small additional blue shift (BS) of the PL. This additional annealing-induced BS has been found, by PR and XRD, to be due to an irradiation-promoted enhancement in In–N bonds formation, whose magnitude appears to not depend on dose within the studied range. [Copyright &y& Elsevier]

The wavelength filtering characteristics of active defective Photonic Band Gap (PBG) waveguides based on dilute nitrides are examined. The analyzed structure is made of GaInNAs-GaInAs MQW ridge waveguides in which a geometrical active defect in the periodic lattice induces selective transmission spectral regions centered at different wavelengths inside the PBG. The device show the advantage of simultaneous DWDM selective filtering and amplification of the filtered signal. The performances of the active PBG filters are investigated as a function of the geometrical and the electrical parameters. The analysis is performed by using proprietary codes, based on the Bidirectional Beam Propagation Method with the Method of Lines introducing the rate equations. Highly selective 9-channel active filter with minimum value of the bandwidth at half-height transmittance B3dB=0.12 nm has been calculated. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The properties of InGaAsN V-groove QWRs are assessed here by polarization-dependent photoluminescence (PL) and micro-magneto-PL. Both the polarization anisotropy of the QWR emission and the strong dependence of the diamagnetic shift on the orientation of the applied magnetic field confirm the 1D nature of the QWR excitons. Further, the possibility of passivating N impurities by H irradiation is used to estimate the N content ( x) in the QWRs by turning off the effects of N incorporation. Both the H-induced blueshift of the QWR emission (70 meV) and the measured value of the electron effective mass are consistent with x ∼1%. Nitrogen is also found to enhance the In intake in the QWR, likely due to the strain reduction resulting from the smaller lattice parameter of the InGaAsN alloy. Such strain reduction is also responsible for the quick decay of the degree of linear polarization (ρ) of the QWR emission with increasing temperature, indicating a small splitting between the QWR valence-band levels. In fully hydrogenated samples, conversely, ρ remains roughly constant up to ∼240 K, suggesting the recovery of a larger energy separation between the QWR hole states upon N passivation. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: This paper highlights the electrical characterization of three types of the multiple quantum well (MQW) InGaAsN/GaAs heterostructures labelled NI58n, NI59n and NI66n with the nitrogen concentration of about 0.4% and indium content of 12.1%, 13.5% and 13.0%, respectively, using capacitance methods. These MQW InGaAsN/GaAs heterostructures were grown by atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) at various growth conditions. The capacitance-voltage and DLTS measurements of these structures were performed utilizing the measurement system BIORAD DL8000. The CV characteristics measured at different temperatures on all heterostructures show very fine fluctuations of capacitance in the voltage range around 0V, which is suggested to be a result of free carriers’ emission from quantum wells. The absence of GaAs “cap” layer in one of the samples shifted its CV characteristic to lower values of capacity. According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. The presence of the deep level ET1 is clear in all samples and its parameters were calculated by multi level evaluation (the activation energy of the defect which is approx. ΔE T =0.62eV, value of effective capture cross-section of the defect σ T is about 10−16 cm2, and defects concentration N T is about 1014 cm−3). [Copyright &y& Elsevier]

Abstract: In this study, we demonstrated the fabrication and characterization of p-GaAs/i-InGaAsN/n-GaAs double hetero-junction solar cells (DHJSCs). The intrinsic InGaAsN absorption layer which is lattice-matched with GaAs substrates was grown by the metal-organic vapor phase epitaxy (MOVPE) system. The metal-organic sources used in the MOVPE growth induced unintentionally-doped carbon adatoms, and this in turn caused some carbon-related defects. This carbon pollution subsequently deteriorated the optical and electrical characteristics of the dilute nitride material. With ex-situ post-annealing being carried out in the furnace, it could not only modify the crystallinity of the InGaAsN material, but the deterioration in the performance of the dilute nitride solar cell due to the nitrogen incorporation could also be mitigated. After conducting the thermal annealing at 550°C for 1h in nitrogen ambience, the conversion efficiency of the DHJSCs was increased from 0.61% to 4.46% under Air Mass 1.5 Global (1000W/m2, AM1.5G) irradiance. The external quantum efficiency (EQE) spectrum further revealed that the efficiency of DHJSCs had been enhanced significantly owing to the crystalline improvement of the intrinsic InGaAsN absorption layer after the ex-situ post-thermal annealing was implemented. This improvement also led to a significant increase in the short-circuit current. The X-ray photoelectron spectroscopy (XPS) measurement result also showed that the ex-situ thermal annealing contributed to the improvement of crystal quality and the reduction of carbon related defects and clusters in the as-grown InGaAsN absorption layer. [Copyright &y& Elsevier]

Abstract: Dilute nitride InAsN epitaxial layers were produced using both liquid phase and molecular beam epitaxial growth techniques. The spectral features in the photoluminescence of samples containing up to 1% N with emission energies in the mid-infrared spectral region are described and compared. The emission intensities of both LPE and MBE grown materials were found to be comparable. Increasing the N content in the InAsN alloys resulted in a significant increase in the activation energy for thermal quenching of the photoluminescence emission due to a combination of lowering of the conduction band edge and Auger de-tuning. [Copyright &y& Elsevier]

Abstract: The photoconductivity of p-i-n GaInNAs/GaAs multiple quantum well (MQW) mesa structures is investigated. When illuminated with photons at energy greater than the GaAs bandgap, a number of oscillations are observed in the current–voltage I–V characteristics. The amplitude and position of the oscillations is shown to depend upon the temperature, as well as upon the exciting wavelength and intensity. Due to the absence of the oscillations in the dark I–V and at temperatures above T =200K, we explain them in terms of photogenerated electrons escaping from quantum wells via tunnelling or thermionic emission. Magnetic fields up to B =11T were applied parallel to the planes of the QWs. A small voltage shift in the position of the oscillations was observed, proportional to the magnetic field intensity and dependent upon the temperature. Calculation of the Landau level energy separation (16meV) agrees with the observed experimental data. Magneto-tunnelling spectroscopy probes in detail the nature of band- or impurity-like states responsible for resonances in first and second subbands, observing the I–V plot in dark condition and under illumination. The field-dependence of the amplitude of the oscillation peaks in I–V has the characteristic form of a quantum mechanical admixing effect. This enhancement is also probably due to the hole recombination with majority electrons tunnelling in the N-related states of the quantum wells. [Copyright &y& Elsevier]

Abstract: This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method. [Copyright &y& Elsevier]

We have measured the absorption, gain and spontaneous emission spectra of GaInNAsSb (3.3%N), GaInNAs (0.5%N) and GaInAs quantum well structures to compare their merits as laser gain media. The parameters describing the relations between peak gain and current provide only limited insight. From the analysis of absorption spectra we have determined the intrinsic properties of the structures, represented by the product [reduced density of states \times matrix element \times overlap integral], taking account of differences in operating wavelength, well width and confinement. We find only a small variation in this product across the samples. The GaInNAsSb structure has a low radiative recombination current due in part to its low photon energy and also to differences in conduction and valence band densities of states and less inhomogeneous broadening relative to GaInNAs. We speculate that Sb brings benefits as a surfactant producing more homogeneous wells so Sb may also be beneficial in structures at shorter wavelength. However, there is a large non-radiative current in GaInNAsSb and achieving further reductions in the non-radiative current is the major challenge in taking advantage of the good gain potential of this system. [ABSTRACT FROM PUBLISHER]

The reverse-bias current–voltage characteristics of a series of \Ga1\-x\Inx\Ny\As1\-y diodes with bandgap of between 0.87 and 1.04 eV are reported. At low bias, diffusion and generation–recombination currents are dominant at high and low temperatures, respectively. At high reverse bias, the dark current is insensitive to changes in temperature, which is indicative of tunneling current mechanisms. We also observe an exponential dependence of the dark current with the electric field in the mid-bias range for all our diodes, which may be explained by the Poole–Frenkel effect. [ABSTRACT FROM AUTHOR]

Abstract: The electrical and optical characteristics of a set of MBE-grown 1.3μm emitting GaInNAs/GaAs quantum well (QW) resonant cavity light-emitting diodes (RCLEDs) have been analyzed as a function of the growth temperature of the distributed Bragg reflector (DBR) and the contact alloying. The RCLEDs consist of a λ-long microcavity delimited on one side by an 8-pair AlAs/GaAs DBR and on the opposite side by a metallic mirror, with the QW located at one of the antinodes of the standing wave. The structures are designed for extraction of the light through the substrate. Room-temperature electroluminescence at 1.3μm is demonstrated with 38% In and 1.3% N in the quantum well. It is found that the RCLEDs with the DBR grown at the lowest temperature of 670°C show a lower differential slope efficiency and degraded current–voltage characteristics, i.e. higher ideality factor, lower shunt resistance and lower threshold voltage. This degradation can be explained to arise from the higher roughness observed in the DBRs grown at 670°C, which likely enhance the formation of point defects and compositional inhomogeneities in the quantum well. Alloying of the ohmic contacts also results in a widening of the electroluminescence emission, probably due to the degradation of the top metallic mirror sharpness caused by the diffusion of the metal into the GaAs. The best results in terms of differential slope efficiency and electrical characteristics are obtained when the DBRs are grown at 750°C and the contacts are left non-alloyed. [Copyright &y& Elsevier]

Abstract: This paper will describe the first-of-a-kind development and demonstration of dilute nitride strained layer superlattice detectors with detectivity as high as 4×1010 cmHz1/2/W and cut-off wavelength of 11-μm for an LWIR design and a cut-off wavelength of 22-μm for a VLWIR design. The developed dilute nitride SLS detectors are based on ultra-low leakage dilute nitride epitaxial layers and/or strained layer superlattices (SLS) of InAs/InAsSbN and InAs/GaInSbN that could enable high VLWIR detectivities at elevated temperatures and at low cost. [Copyright &y& Elsevier]

Abstract: The effect of atomic hydrogen irradiation during molecular beam epitaxy (MBE) on the electrical properties of GaInNAs thin films and the characteristics of homojunction GaInNAs solar cells are presented. We found that an optimum amount of atomic H flux irradiated during MBE growth of GaInNAs material is effective for suppressing or passivating the defects that act to mainly trap the electrons. Furthermore, an enhanced layer-by-layer growth improves the uniformity of GaInNAs layers thereby reducing the segregation and clustering of N atoms. A p–i–n Ga0.984In0.016N x As1− x solar cell fabricated by atomic H-assisted MBE shows a short-circuit current density of 22.2mA/cm2. [Copyright &y& Elsevier]

Low-bandgap GaInNAsSb single junction solar cells incorporating a planar Au back surface reflector for enhancing the photocurrent generation are reported. In particular, a 700 nm thick GaInNAsSb junction with a bandgap of 0.78 eV (corresponding to 6.2% N) incorporating the back reflector exhibited a short-circuit current density of 15.2 mA/cm2 for AM1.5D (1000 W/m2) illumination, when placed underneath a GaAs-filter mimicking the operation of a multijunction architecture. The corresponding external quantum efficiency represents the highest external quantum efficiency reported so far for dilute nitride solar cells with bandgaps below 0.8 eV. Electrical simulations reveal that the relatively high value of the quantum efficiency is attributed to a low p-type carrier concentration and partially to the varying doping level in the GaInNAsSb region. Moreover, the absorption coefficients for low-bandgap GaInNAsSb materials are estimated and used in a comprehensive optical analysis to understand the photon harvesting performance of the solar cells with reflector. The analysis reveals incomplete absorption in the GaInNAsSb layers for the double-pass configuration enabled by the planar back reflector pointing to the need for deploying more advanced structured reflectors. However, the structures exhibited high collection efficiencies laying the foundation for further improvements of the quantum efficiency values. Moreover, the low-bandgap dilute nitride solar cells show potential to meet the current-matching requirements in next-generation multijunction devices with five or more junctions, thus being a prospective alternative for replacing Ge as the bottom junction. • First demonstration of a low-bandgap (0.8 eV) GaInNAsSb solar junctions incorporating a back surface reflector. • Highest quantum efficiency reported for low-bandgap GaInNAsSb/GaAs-based solar cells. • First report on absorption coefficients for 0.8 eV GaInNAsSb materials. • Proving the potential of low-bandgap GaInNAsSb to achieve current matching in advanced solar cells with 5 or more junctions. [ABSTRACT FROM AUTHOR]

We present an experimental and theoretical investigation of the temperature dependence of the threshold current for double quantum well GaInNAs-GaAs lasers in the temperature range 10 °C-110 °C. Pulsed measurements of the threshold current have been performed on broad and narrow ridge wave guide (RWG) lasers. The narrow RWG lasers exhibit high characteristic temperatures (To) of 200 K up to a critical temperature (Tc), above which To is reduced by approximately a factor of 2. The To -values for broad RWG lasers are significantly lower than those for the narrow RWG lasers, with characteristic temperatures on the order of 100 (60) K below (above) Tc. Numerical simulations, using a model that accounts for lateral diffusion effects, show good agreement with experimental data and reveal that a weakly temperature dependent lateral diffusion current dominates the threshold current for narrow RWG lasers. [ABSTRACT FROM AUTHOR]

Abstract: We employ the optically detected magnetic resonance (ODMR) technique to study and identify important grown-in defects in Ga(In)NP grown by molecular-beam epitaxy (MBE). Several types of defects were revealed from ODMR studies. The dominant defects were found to be related to Ga interstitials, evident form their characteristic hyperfine interaction arising from the spin interaction between the electron and the Ga nucleus. Some other as yet unidentified intrinsic defects were also found to be commonly present in the alloys. The effects of growth conditions (ion bombardment, N2 gas flow, etc.) and post-growth rapid thermal annealing on the formation of these defects were studied in detail, shedding light on the formation mechanism of defects. [Copyright &y& Elsevier]

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga1- x In x N y As1- y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (d E/d T) is tabulated as a function of nitrogen concentration and the type of dopant. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the optical properties of GaInNAs quantum dot (QD) structures, emitting at 1.55 µm wavelength. The theoretical model is based on a 10 × 10 k · p band-anti-crossing Hamiltonian, incorporating valence, conduction and nitrogen-induced bands. We have investigated the influence of the nitrogen to the conduction band mixing, and piezoelectric field on the ground state optical matrix element. For QDs grown on GaAs substrate with a reduced amount of indium and an increased amount of nitrogen in the QD the e x polarized optical matrix element becomes on the average larger and less sensitive to the variation of both the QD shape and size than is the case of an InNAs QD. For the QD grown on InP substrate the dominant optical dipole matrix element is of the e z light polarization. Our results identify the specific In and N content in the QDs required for optimal long-wavelength emission on both substrates. [ABSTRACT FROM AUTHOR]

Abstract: Ultra-high-resolution infra-red local vibrational mode (IR LVM) spectroscopy measurements together with density-functional calculations have been used to identify the signatures of close substitutional nitrogen () pairs in alloys with concentrations of . We show that the presence of sub-peaks close to the absorption band can be attributed to nitrogen pairs up to fourth neighbor position. Additionally, we suggest that the nitrogen pairs which give rise to the deepest levels below the conduction band edge are the first to be removed upon annealing. [Copyright &y& Elsevier]

Abstract: Highly mismatched alloys (HMAs) are dilute alloys whose fundamental properties are dramatically modified through the substitution of a relatively small fraction (up to ∼5%) of host atoms with a very different element. Specific examples are dilute III–V nitrides (e.g. GaN x As1−x ) and II–VI oxides (e.g. ZnO x Te1−x ) in which the conduction bands are strongly modified by the anticrossing interaction between localized states of O or N and the extended states of the semiconductor matrix. Using a highly non-equilibrium method: the combination of ion implantation and pulsed laser melting (II-PLM) we have synthesized a wide variety of III-N x -V1−x and II-O x -VI1−x alloys with N or O content up to 2%. The structural and optical properties of these HMAs have been systematically investigated. In particular, we demonstrated that the Zn1−y Mn y O x Te1−y dilute oxide is a multiband alloy that can be used for the realization of the single junction, high efficiency intermediate band solar cells. [Copyright &y& Elsevier]

Dilute nitride GaInNAs and GaInNAsSb alloys grown on GaAs have quickly become excellent candidates for a variety of lower cost 1.2–1.6 μm lasers, optical amplifiers, and high power Raman pump lasers that will be required in the networks to provide high speed communications to the desktop. Because these quantum well active regions can be grown on GaAs, the distributed mirror technology for vertical cavity surface emitting lasers coupling into waveguides and fibers and photonic crystal structures can be readily combined with GaInNAsSb active regions to produce a variety of advanced photonic devices that will be crucial for advanced photonic integrated circuits. GaInNAs(Sb) provides several new challenges compared to earlier III–V alloys because of the limited solubility of N, phase segregation, nonradiative defects caused by the low growth temperature, and ion damage from the N plasma source. This paper describes progress in overcoming some of the material challenges and progress in realizing record setting edge emitting lasers, the first VCSELs operating at 1.5 μm based on GaInNAsSb and integrated photonic crystal and nanoaperture lasers. [ABSTRACT FROM AUTHOR]

Abstract: GaIn(N)As/GaAs and GaIn(N)As/GaNAs/GaAs quantum well samples, with and without GaNAs strain-compensating layers (SCL), were grown on GaAs (001) substrates by molecular beam epitaxy. Photoluminescence (PL) was used to study the effects of the GaNAs SCL on the properties of the Ga(In)NAs QWs upon annealing. It is found that an extra blue-shift (ΔE =5.2 meV) in the PL emission from the GaInNAs QW sample at the initial annealing stage (t ann =40 s) was induced by the GaNAs SCLs. However, for the GaInAs QW sample, the blue-shift induced by GaNAs SCL is only 1.1 meV. As the annealing time was increased, the blue-shift of both GaInNAs and GaInAs QWs showed saturations at 16 meV and 8 meV, respectively. The PL blue-shifts were much enhanced by inserting GaNAs SCLs showing a non-saturable behavior. X-ray diffractions from the strain compensated GaIn(N)As QWs before and after annealing show no N atom diffusion but Ga/In atom interdiffusion across the QW interfaces. The Ga/In atom interdiffusion caused by annealing was also confirmed by high-resolution transmission electron microscopy from the GaInNAs/GaAs QW sample. [Copyright &y& Elsevier]

Abstract: GaN x As1−x multiple-quantum-well (MQW) samples (x ≤0.025) grown by molecular beam epitaxy have been studied by photoluminescence (PL) spectroscopy, high-resolution X-ray diffraction (HR-XRD), secondary-ion mass spectrometry (SIMS) and ultra-high-resolution infrared local-vibrational-mode (IR LVM) spectroscopy in order to determine their compositional and structural properties. Compositional data from PL spectroscopy and HR-XRD, derived using simple models of the superlattice structure, show good agreement. SIMS depth profiles show that the wells are triangular, and are wider and shallower than predicted, with nitrogen present in the barrier layers. A comparison between SIMS and HR-XRD suggests the presence of interstitial nitrogen for samples with the highest nominal concentrations. By contrast, IR LVM measurements demonstrate that substitutional nitrogen incorporates linearly with increasing nitrogen fraction. [Copyright &y& Elsevier]

Abstract: We present a theoretical study of the electronic structure and optical properties of zinc-blende GaSb1− x N x semiconducting dilute alloys for small amounts of N (0⩽x⩽0.05). Our calculations are based on the pseudo-potential scheme within the virtual crystal approximation that takes into consideration the effects of compositional disorder. In agreement with previous studies, it is found that the introduction of only a few percent of N into GaSb reduces substantially the energy band gaps. It is shown that GaSb1− x N x can be a direct or an indirect semiconductor depending on the N content. Negative band gaps in the material of interest are predicted to occur when the N concentration exceeds 0.026. The information derived from the present study shows that GaSb1− x N x (0⩽x⩽0.017) should enable access to wavelengths in the 2–4μm range. [Copyright &y& Elsevier]

Abstract: Recently, the growth of patterned surfaces is being used to demonstrate the site control of the three-dimensional nanostructures, and in particular quantum dots. Nevertheless the pre-patterning techniques show some disadvantages. In this work, we report a novel in situ hole-patterning technique which consists of growing by molecular beam epitaxy a dilute nitride GaAsN layer on 1° and 2° towards [2¯11] misoriented GaAs(111)B substrates. Later, we carry out a regrowth of GaAs layers on this patterned surfaces in order to improve the surface quality and the homogeneity of the characteristics of holes (size, depth, etc.). Consecutively, we use these patterned surfaces to grow InAs quantum dots, whose growth on these misorientations results in a greater difficulty. A structural characterization of the resulting samples, both hole-patterns and quantum dots, has been performed. Besides, we have realized studies of the dependence of the surface morphology on some important parameters (including substrate misorientation, thicknesses of the GaAsN and GaAs layers grown and growth conditions). [Copyright &y& Elsevier]

Abstract: Contactless electroreflectance (CER) spectroscopy has been applied to investigate the optical transitions in Ga(In)NAs/GaAs quantum well (QW) structures containing Sb atoms. The identification of the optical transitions has been carried out in accordance with theoretical calculations which have been performed within the framework of the effective mass approximation. Using this method, the bandgap discontinuity for GaN0.027As0.863Sb0.11/GaAs, Ga0.62In0.38As0.954N0.026Sb0.02/GaAs, and Ga0.61In0.39As0.963N0.017Sb0.02/GaN0.027As0.973/GaAs QW structures has been determined. It has been found that the conduction-band offset is ∼50 and ∼80% for GaN0.027As0.863Sb0.11/GaAs and Ga0.62In0.38As0.954N0.026Sb0.02/GaAs QWs, respectively. It corresponds to 264 and 296meV depth QW for electrons and heavy-holes in GaN0.027As0.863Sb0.11/GaAs QW; and 520 and 146meV depth QW for electrons and heavy-holes in Ga0.62In0.38As0.954N0.026Sb0.02/GaAs QW. In the case of the Ga0.61In0.39As0.963N0.017Sb0.02/GaN0.027As0.973/GaAs step-like QW structure it has been shown that the depth of electron and heavy-hole Ga0.61In0.39As0.963N0.017Sb0.02/GaN0.027As0.973 QW is ∼144 and ∼127meV, respectively. [Copyright &y& Elsevier]

Abstract: The pressure dependence of optical transitions in Ga0.64In0.36As/GaAs and Ga0.64In0.36N0.01As0.99/GaAs single quantum well (SQW) structures were studied in photoreflectance (PR) spectroscopy. In order to apply high hydrostatic pressure, up to ∼11kbar, the liquid-filled clamp-pressure cell with a sapphire window for optical access has been adopted in the PR set-up with the so called ‘bright configuration’. It has been found that the linear hydrostatic pressure coefficient for the ground state transition are equal to 8.6 and 7.3meV/kbar for the GaInAs/GaAs and GaInNAs/GaAs SQWs, respectively. This result shows that the incorporation of only 1% of N atoms into GaInAs/GaAs leads to ∼15% decrease in the pressure coefficient. In addition, a non-linearity in the pressure dependence of the ground state transition has been resolved for the GaInNAs/GaAs SQW. [Copyright &y& Elsevier]

Abstract: Raman scattering of coherently strained GaN x As1−x alloys grown on GaAs (001) substrates by molecular beam epitaxy has been investigated in the temperature range of 80–150 K. The intensity of GaAs-like longitudinal optical (LOGaAs) phonon and nitrogen-localized vibration mode (NLVM) decrease with temperature and the line width of both these modes show substantial broadening at higher temperatures. Temperature dependence of phonon line width and peak frequency of LOGaAs modes were analyzed in terms of anharmonic damping effect induced by thermal and compositional disorder. It is found that the anharmonicity is higher for GaNAs than that for GaAs, and increases with N concentration in GaNAs alloys. Both thermal- and disorder-induced anharmonicities can change the line width, line frequency, and lifetime of LOGaAs mode in GaNAs alloys. These results obtained from Raman investigation would lead to a better understanding of the anharmonic effects in dilute nitrides. [Copyright &y& Elsevier]

We consider two GaAs-based laser materials emitting at telecommunication wavelengths, namely the dilute nitride (GaIn)(NAs) as well as Ga(AsSb), and model their optical properties by including scattering and dephasing on a microscopic basis. The theory shows an excellent agreement with experiment without the inclusion of fit parameters such as phenomenological scattering times. By careful comparison of measurements and computations, one can extract controversial bandstructure parameters such as the band offset. [ABSTRACT FROM AUTHOR]

Abstract: Using the pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model, we have studied the effect of nitrogen content x (0< x ≤0.05) on mechanical properties of GaAs1−x N x dilute alloys in zinc-blende structure. The agreement between our results and the available experimental data is found to be satisfactory. We have found that except for the anisotropy factor and the [100] Poisson ratio, the incorporation of only a few percentage of nitrogen affects the mechanical properties being studied here. In addition, the effect of compositional disorder on the calculated parameters has been examined and found to have an important effect on most studied quantities. [Copyright &y& Elsevier]