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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]

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]

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 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 a time-resolved photoluminescence study for GaInNAs and GaNAsSb p-i-n bulk solar cells grown on GaAs(100). In particular, we studied the extent to which the carrier lifetime decreases with the increase of N content. Rapid thermal annealing proved to significantly increase the decay times by a factor of 10 to 12 times, for both GaInNAs and GaNAsSb heterostructures, while for the 1-eV bandgap GaNAsSb structure, grown at the same growth conditions as the GaInNAs, the photoluminescence decay time remained slightly below 100 ps after annealing; the approximately 1.15-eV GaInNAs p-i-n solar cell exhibited a lifetime as long as 900 ps. PACS: 78.47.D; 78.55.Cr; 88.40.hj [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]

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 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]

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: 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: We present time-resolved photoluminescence (PL) results of a series of samples with x up to 0.01. The temperature dependence, the concentration dependence as well as the temporal behavior indicate that the PL is dominated by excitation transfer processes between the extended band states and localized N-related states (such as the isolated N-impurity, various N-pair states and higher N-clusters) as well as by excitation transfer between the various localized N-related states themselves. The excitation transfer processes in conjunction with the concentration-dependent statistics of the various N-related states alone are sufficient to explain the observed red-shift of the luminescence of with increasing x as well as the spectral dependence of the PL decay times. However, this implies that the PL data alone do not give any conclusive evidence that a hard transformation from an indirect to a direct-gap semiconductor takes place in Ga(N,P) with increasing N up to 2% as often stated. [Copyright &y& Elsevier]

Dilute nitrides are promising alloys in view of extending potential micro- and opto-electronics applications of GaAs technology. Orientation effects on nitrogen incorporation in GaAs have been scarcely addressed. Here, GaAsN on (1 0 0) and on As(B)- and Ga(A)-rich (1 1 1) substrates was grown by molecular beam epitaxy at different substrate temperatures. Nitrogen content measured by secondary ion mass spectrometry as a function of the growth temperature highlights the influence of orientation on nitrogen incorporation. Furthermore, thermal annealing is shown to improve the optical quality of GaAsN quantum wells whatever their substrate orientations. [Copyright &y& Elsevier]

We use a combination of magneto-tunnelling and photoluminescence spectroscopy techniques to explore the admixing of the extended GaAs conduction band states with the localised N-impurity states in dilute GaAs1−yNy quantum wells (QWs) incorporated in resonant tunnelling diodes. When y is increased from 0% to 0.08%, the current resonance due to electrons tunnelling through the lowest quasi-bound state of the QW splits into two main features due to electron tunnelling into the N-induced E− and E+ hybridised subbands of the GaAs1−yNy layer. These subbands have a very well-defined character even for a small N-content (∼0.08%) and have non-parabolic energy–momentum dispersions. A further increase of y smears out the resonances and quenches the current due to electron trapping on strongly localised N-levels. [Copyright &y& Elsevier]

Electron irradiation is found to cause a large blue shift of photoluminescence from a 1.3-μm laser-like strain-compensated GaInNAs/GaNAs/GaAs quantum well structure when annealed after irradiation. The line shift is assigned to the presence of complex defect centers in the quantum wells. The defects are very unstable. The peak position and line shape of the spectra are restored to their original values by an ageing effect, which occurs even at room temperature. The mechanism causing the blue shift/red shift of photoluminescence is qualitatively described. [ABSTRACT FROM AUTHOR]

Abstract: The use of a nitrogen electron cyclotron resonance (ECR) plasma source has allowed the growth of GaAsN at GaAs substrate temperatures as high as 600°C, unlike the case for growth using radio frequency (RF) plasma sources, for which there is significant loss of nitrogen at substrate temperatures as low as 480–520°C. Photoluminescence (PL) intensities are significantly improved at a substrate temperature of 600°C and are further improved slightly by using an ion trap to extract charged species from the beam. As the trap voltage is increased there is a reduction in the total nitrogen concentration, as measured by secondary ion mass spectrometry (SIMS), and a slight increase in the active nitrogen concentration, as measured by PL. These observations are consistent, for example, with charged and active nitrogen species together being involved in the formation of point defects, however more work is needed to clarify what may well prove to be a complex situation. [Copyright &y& Elsevier]

Abstract: Dilute GaAsN layers are grown by liquid phase epitaxy (LPE) technique, using polycrystalline GaN as the source of nitrogen. A band gap lowering of 100 meV is obtained from low temperature photoluminescence (PL) measurements which correspond to a little more than 0.5% nitrogen in the layer. Using 10 K photocapacitance measurements, a 0.7 eV electron trap is detected in the material which is assigned to an interstitial (N–N)As defect. Annealing of the material at 750 °C for 1 h greatly reduced this trap and new electron traps with activation energies of 0.8 and 0.9 eV are detected. These new traps are suggested to be due to individual nitrogen-related defect complexes, produced by the thermal annihilation of the N–N bond. After a high temperature treatment of the GaAsN growth melt with 0.1 wt.% Er, nitrogen is found to be removed from the layer and no electron trap was detected. [Copyright &y& Elsevier]

This work investigates the effect of the thickness of the epitaxial layer (100 nm and 1 μm) on the optical properties of quaternary GaAs 0.1 P 0.89 N 0.01 alloys. Furthermore, the effect of rapid thermal annealing (RTA) on their properties has been studied using the Photoluminescence (PL) technique. Increasing the thickness of the epilayer led to an enhancement of the PL intensity as well as the energy bandgap, which was shifted to higher energy (from 1.82 eV in 100 nm to 1.94 eV in 1 μm layer). However, the 1.94 eV bandgap energy is not ideal for solar cells based materials grown on GaP substrates. Post-growth thermal annealing by rapid thermal annealing (RTA) for both samples resulted in an enhancement in the optical properties as observed by a decrease of the Full Width at Half Maximum (FWHM) and an increase of the PL intensity. Therefore, all results obtained in this study indicate that GaAs 0.1 P 0.89 N 0.01 with 100 nm epilayer thick is better choice to fabricate good efficiency solar cells based materials on GaP substrates as compared to 1 μm sample. • PL investigation of the effect of thickness and thermal annealing on the optical properties of GaAs 0.1 P 0.89 N 0.01 alloys. • Increasing the GaAs 0.1 P 0.89 N 0.01 epilayer thickness leads to an enhancement of the PL intensity and the energy bandgap. • RTA improves the optical properties of both thin and thick as-grown GaAs 0.1 P 0.89 N 0.01 epilayers but PL energy blue shifts. • PL blue shift after RTA is assigned to a decrease of point defects and localized states radiative effects. • Observation of S-shaped bandgap energy in as-grown and annealed 1 μm thick GaAs 0.1 P 0.89 N 0.01 due to N localization effect. [ABSTRACT FROM AUTHOR]

GaAsN and GaInAsN have been grown on As(B)- and Ga(A)-rich {1 1 1} substrates by molecular beam epitaxy. N incorporation has been found to be highly dependent on the substrate orientation. The influence of growth conditions on optical properties of (1 1 1)A and (1 1 1)B oriented GaAsN quantum wells has been determined. The better orientation appears to be the Ga-rich one for GaAsN and GaInAsN/GaAs wells. [Copyright &y& Elsevier]