GaAsN Alloys Research Articles

Onset of tetrahedral interstitial formation in GaAsN alloys

Onset of tetrahedral interstitial formation in GaAsN alloys

Light helicity probed through spin dependent recombination in GaAsN alloys

In this paper we briefly review the main experimental and theoretical aspects of the spin-dependent recombination in dilute nitride GaAsN point interstitial defects leading to a large contrast between the photoluminescence intensity under circularly and linearly polarized light excitations as well as to the implementation of a chiral photodetector. We discuss the interplay of the spin-selective capture of free electrons in deep paramagnetic Ga2+ interstitial defects and the hyperfine coupling among the defect nucleus and the bound electron. These factors combined confer GaAsN the capability of discriminating the handedness of an incident light beam.

P-n nanostructure formation effect of low-energy N2+ ions on n-GaAs surface

The electronic structure and chemical composition of the n-GaAs surface after implantation of N2+ ions with energy Ei = 3000 eV and fluence Q ∼ 3 × 1015 cm−2 were studied by synchrotron-based X-ray photoelectron spectroscopy to clarify effects of low-energy nitrogen ion implantation on A3B5 semiconductor surfaces. Conversion of the conductivity type and creation of a p-n structure on the n-GaAs surface were revealed under N2+ ion irradiation. The conductivity type transformation was shown to occur due to pure mechanical action of nitrogen ions, resulting in formation of Ga anti-site acceptors. The ∼ 10 nm-thick p-layer obtained consisted of concentrated GaAs1-xNx (x ∼ 0.1) alloy whose bandgap width is known to be essentially narrower compared to the pristine GaAs semiconductor. Therefore, the structure formed is a nano-heterosctructure incorporating the semiconductor alloy whose properties are considered to be attractive for infrared applications. The obtained GaAsN electron binding energies (EB (N1s) = 397.0 eV, EB (Ga3d) = 19.42 eV and EB (As3d) = 41.25 eV) can be used for identification of the GaAsN alloy phase. An approach to 3D p-n structures formation was suggested using nitrogen ion beam without wet lithography.

GaAs1-xNx candidate material for a high efficiency based homojunction solar cell

The GaAsN alloy has a great potential in the manufacture of the photovoltaic devices. A simple optimized GaAsN junction can reach conversion efficiency from > 20%, comparable with that reached by the best cells of die CISGS. Because the band gap of GaAsN can be modified from 1.4 eV to 3.4 eV by increasing the nitrogen content with multi-junction cells, it is theoretically possible to achieve the record performance 70% with this only material system, whereas the theoretical record in technology GaAs multi-junctions is less than 50%. The work presented in this paper concerns the study of photovoltaic cells based on GaAsN nitrided materials. The main objective is to optimize the front and base with their thickness and doping, on the electrical characteristic of the photovoltaic cell and subsequently its output parameters under solar illumination of AM1.5G. 54.1 % efficiency is predicted for this new GaAs1-xNx based on a simple single solar cell. This structure can also provide a fundamental solar cell unit for developing very high efficiency IBSC solar cell.

Opposite Hydrogen Behaviors in GaAsN and InAsN Alloys: Band Gap Opening Versus Donor Doping

Experiments suggest that atomic H neutralizes the effects of N (i.e., it recovers the host energy gap) without inducing any band filling effect (i.e., without behaving as a shallow donor) in the Ga...

PL characterization of GaN nanolayer obtained by N ion implantation into Si3N4/GaAs

Photoluminescence measurements (PL) and Transmission Electron Microscopy (TEM) were employed to characterize the GaN nanolayer (~70 nm) obtained by Ion Beam Synthesis (IBS). N+ ions at 50 keV were implanted up to a fluence of 3 × 1017 cm−2 into a GaAs (001) capped by 125 nm Si3N4 layer. N+ implantation was performed with samples held at 450 °C and subsequently annealed in a temperature range between 550 and 1000 °C for 5 min by Rapid Thermal Annealing (RTA) under N2 flow. An amorphous GaAsN alloy is obtained at the as-implanted state, which is converted to a N-rich GaN-nanolayer only after annealing at 850 °C. However, the band-gap emission at 3.4 eV (FWHM = 0.63 eV) is present already in the spectrum from the as-implanted sample, and it does not significantly change in shape and intensity after any annealing temperature up to 850 °C. It was additionally observed three more emission bands: 2.34 eV (FWHM = 0.48 eV), 2.63 eV (FWHM = 0.34 eV) and 2.92 eV (FWHM = 0.31 eV) that might be due to VGa and VGa clusters in the N-rich GaN-nanolayer. The 850 °C annealing increases their intensities by factors of 1.34, 1.43, and 1.61, respectively, when compared to the as-implanted sample. Therefore, the optical signature for the formation of an ion beam synthesized N-rich GaN-nanolayer does not come from an increase in the band-gap emission but by an increase in the bands associated with defects. The emission from the sample annealed at 1000 °C is majority from the defect bands which were intensified by a factor of ~10.

Surfactant-induced chemical ordering of GaAsN:Bi

We have examined the influence of an incorporating surfactant on chemical ordering in GaAsN:Bi alloys. Epitaxy with a (2 × 1) reconstruction leads to the formation of GaAsN alloys, while the introduction of a Bi flux induces long-range chemical ordering of the {111} planes of GaAsN:Bi. We propose a mechanism in which Bi enhances the alignment of dimer rows along the [110] direction, facilitating N incorporation beneath surface dimers and Bi incorporation between dimer rows to form alternating N-rich and Bi-rich {111} planes. These findings suggest a route to tailoring the local atomic environment of N and Bi atoms in a wide range of emerging dilute nitride-bismide alloys.

Formation energies of substitutional NAs and split interstitial complexes in dilute GaAsN alloys with different growth orientations

To quantitatively evaluate the formation energies of the (N–N)As/(N–As)As/(As–As)As split interstitials in dilute GaAsN alloys, first-principles total-energy calculations using a projector augmented wave method are performed. The formation energies for different defects are calculated as a function of the atomic chemical potentials of constituent elements. We compare the formation energies for the NAs substitution and split interstitial complexes based on the traditional (100) and high-index GaAs (311) A/B plane under Ga-rich and As-rich conditions. According to the results of comparison, the chemical potential condition of forming-related defect and the dominant defect for all planes are determined.

High nitrogen composition–induced low interfacial roughness of GaAs0.978N0.022/GaAs multiple quantum wells grown through solid-source molecular beam epitaxy

GaAs1−xNx/GaAs multiple quantum wells (MQWs) were grown on GaAs(001) substrates through solid-source molecular beam epitaxy under various nitrogen background pressures (NBPs), and the crystal quality at the interface of GaAs1−xNx and GaAs was investigated. X-ray diffraction and electron microscopy confirmed the low interface roughness of MQWs grown at a NBP of 5×10−6Torr. Surface morphology measurements revealed a smooth surface without whisker-like defect structures. The fabricated MQWs exhibited high photoluminescence intensity because of the reduction in surface recombination with high nitrogen incorporation. Raman spectroscopy confirmed the presence of N-like local vibrational mode, and this was attributed to the presence of phase separation in GaAsN alloys. Rapid thermal annealing improved photoluminescence intensity by 100-fold and substantially reduced full width at half maximum because of MQW homogenization. These results evidence the favorable crystal interface of GaAs0.978N0.022 alloys. Hence, GaAs0.978N0.022/GaAs MQWs grown under high pressure might be useful in fabricating optoelectronic devices.

Spin-dependent recombination in GaAs1–x N x alloys at oblique magnetic field

We have studied experimentally and theoretically the optical orientation and spin-dependent Shockley-Read-Hall recombination in a semiconductor in a magnetic field at an arbitrary angle between the field and circularly polarized exciting beam. The experiments are performed at room temperature in GaAsN alloys where deep paramagnetic centers are responsible for the spin-dependent recombination. The observed magnetic-field dependences of the circular polarization r(B) and intensity J(B) of photoluminescence can be approximately described as a superposition of two Lorentzian contours, normal and inverted, with their half-widths differing by an order of magnitude. The normal (narrow) Lorentzian contour is associated with depolarization of the transverse (to the field) component of spin polarization of the localized electrons, whereas the inverted (broad) Lorentzian is due to suppression of the hyperfine interaction of the localized electron with the defect nucleus. The ratio between the height of one Lorentzian and depth of the other is governed by the field tilt angle. In contrast to the hyperfine interaction of a shallow-donor-bound electron with a large number of nuclei of the crystal lattice, in the optical orientation of the electron-nuclear system under study no additional narrow peak appears in the oblique field. This result demonstrates that in the GaAsN alloys the hyperfine interaction of the localized electron with the single nucleus of the paramagnetic center remains strong even at room temperature. For a theoretical description of the experiment, we have extended the theory of spin-dependent recombination via deep paramagnetic centers with the nuclear angular momentum I = 1/2 developed previously for the particular case of the longitudinal field. The calculated curves r(B), J(B) agree with the approximate description of the experimental dependences as a sum of two Lorentzians.

<p class="IJOPCMTitle">A study on structural and electronic properties of GaAs<sub>1-x</sub>N<sub>x </sub>and GaAs<sub>1-x</sub>Bi<sub>x</sub> alloys</p>

<p>We have performed first principles method to investigate structural and electronic properties of GaAs<sub>1-x</sub>N<sub>x</sub> and GaAs<sub>1-x</sub>Bi<sub>x</sub> ternary semiconductor alloy using Density Functional Theory and pseudo potential method within the Generalized Gradient Approximations and Local Density Approximation. The Zinc-Blende phase is found stable for GaAsN and GaAsBi alloys. In this study we investigate the both bowing parameters changing with Bismuth concentration in GaAsBi and Nitrogen concentration in GaAsN alloys. By using the bowing parameter of GaAsBi and GaAsN alloys we obtained the bandgap energies for all x concentrations (0 < x < 1) and lattice constant of both alloys which are important for wide range device application. For studied materials, lattice parameters and band gap energies are compared with available theoretical and experimental works.</p>

Growth and characterization of GaAs1−x−ySbxNy/GaAs heterostructures for multijunction solar cell applications

The GaAsSbN dilute-nitride alloy can be grown lattice-matched to GaAs with a bandgap of 1 eV, making it an ideal candidate for use in multijunction solar cells. In this work, using molecular beam epitaxy in conjunction with a radio-frequency nitrogen plasma source, the authors focus first on the growth optimization of the GaAsSb and GaAsN alloys in order to calibrate the Sb and N compositions independently of each other. After the optimum growth conditions to maintain two-dimensional growth were identified, the growth of GaAsSbN films was demonstrated. Both a GaAsSb0.076N0.018/GaAs heterostructure (100 nm thick) and a GaAsSb0.073N0.015/GaAs quantum well (11 nm thick) were grown. X-ray diffraction analysis reveals quite high crystal quality with a small lattice mismatch of 0.13%–0.16%. Secondary ion mass spectrometry profiling revealed that nitrogen was unintentionally incorporated in the GaAs buffer layer during the plasma ignition and stabilization. Nevertheless, a low temperature photoluminescence peak energy of 1.06 eV was measured for the GaAsSbN heterostructure sample while the quantum well emitted photoluminescence at 1.09 eV, which demonstrates promise for realizing 1-eV solar cells.

First-principles calculation of band-gaps reduction in GaAsN alloys and (110) growth axis GaAs/GaN superlattice

First-principles calculations are performed to study the structural and electronic properties of GaAs and GaN zinc-blende/zinc-blende superlattices using the full potential linear muffin-tin orbitals method in its plane wave approximation which enables an accurate treatment of the interstitial regions. The choice of this method ensures the present work to be free from adjustable parameters and enabled us to perform a microscopic study. The results for GaAs/GaN superlattices with both (001) and (110) growth axis are investigated and compared. We have found that bowing, which is known to occur for ternary GaAsN dilute nitrides, is absent from GaAs/GaN “dilute nitride” of (001) growth axis superlattices for N concentrations beyond 7%, but it can be obtained in the (110) system.

Molecular-beam epitaxy growth of dilute GaAsN alloys by surface nitridation

This paper presents the growth of GaAsN pseudo-alloys by a surface nitridation method that consisted of a repeated cycle of nitridation of the GaAs (001) surface, growth interruption and growth of a GaAs overlayer. Surface reconstruction during the nitridation process changed from (2×4) to (1×4) and (3×4) phases above 540°C with the increase of nitridation time, resulting in a higher N compositions of the alloys. It was revealed that an excessive nitridation resulted in the degradation of the photoluminescence (PL) intensity. While the N composition slightly decreased with the interruption time, less impact appeared on their crystallinity characterized by PL measurement. As a result, the N composition was controllable between 1% and 5% by the combination of growth temperatures (460–600°C) and thicknesses of the GaAs overlayer (2–8 monolayers; MLs). The thickness of the GaAs overlayer should be designed over 4 ML to form a flat surface for the next nitridation process. The integrated PL intensity of GaAs0.97N0.03 alloys was increased by 7 times compared to the one grown by conventional growth method (continuous supply), indicating the improved crystalline quality of the GaAsN alloys.

Identifying the dominant interstitial complex in dilute GaAsN alloys

Significant composition-dependent incorporation of N into non-substitutional sites is often reported for dilute GaAsN alloys. To distinguish (N-N)As, (N-As)As, and (AsGa-NAs) complexes, we compare Rutherford backscattering spectrometry and nuclear reaction analysis (NRA) spectra with Monte Carlo-Molecular Dynamics simulations along the [100], [110], and [111] directions. For the Monte Carlo simulation, we assume that (N-N)As is aligned along the [111] direction, while (N-As)As is aligned along the [010] direction. The measured channeling NRA spectra exhibit the highest (lowest) yield in the [111] ([100]) directions. Similar trends are observed for simulations of (N-As)As, suggesting that (N-As)As is the dominant interstitial complex in dilute GaAsN.

Growth orientation dependence of Si doping in GaAsN

The incorporation of Si in GaAsN alloys grown simultaneously on (100), (311)A, (311)B, and (211)B GaAs substrates by the chemical beam epitaxy has been investigated. The decrease in electron concentration with the increasing N composition suggests the occurrence of N and Si interaction, whereas the interaction exhibits evidently different extent depending on the growth orientation. Combined with the secondary ion mass spectrometry and photoluminescence measurements, it is revealed that (311)B and (211)B are the promising substrate orientations to reduce the N-Si passivation and improve n-type Si doping in GaAsN over a wider N composition range. A surface bonding model is utilized to explain the plane polarity dependent incorporation behaviors of Si and N.

Electron impact induced collective and atomic-like single-electron Ga3d → εl excitations in GaAsN alloy

Nitride nanolayer of about 4nm thickness formed on the GaAs (100) surface by N2+ ion bombardment with energy Ei=2500eV has been studied in situ by electron energy loss spectroscopy (EELS). Collective (plasmonic) and single-electron excitations were resolved in the EELS spectrum. Analysis of the plasmonic contributions from different chemical phases showed domination of the phase of GaAsN alloy in the nitrated layer. Single-electron excitations were shown to be related to the transitions from core- and valence band states into unoccupied local atomic-like states Ga3d→εl and “GaAs4p”→εl. The model of the atomic-like state formation in a temporary quantum dot near Ga atom was assumed. It has been shown that analysis of collective and single-electron excitations enables synchronous EELS diagnostics of both the chemical composition and unoccupied states of GaAs nitrides.

Optical density of states in ultradilute GaAsN alloy: Coexistence of free excitons and impurity band of localized and delocalized states

Optically active states in liquid phase epitaxy-grown ultra-dilute GaAsN are studied. The feature-rich low temperature photoluminescence spectrum has contributions from excitonic band states of the GaAsN alloy, and two types of defect states—localized and extended. The degree of delocalization for extended states both within the conduction and defect bands, characterized by the electron temperature, is found to be similar. The degree of localization in the defect band is analyzed by the strength of the phonon replicas. Stronger emission from these localized states is attributed to their giant oscillator strength.

Photoreflectance study of the temperature dependence of excitonic transitions in dilute GaAsN alloys

We have studied the temperature dependence of optical transitions in dilute GaAsN alloys using photoreflectance (PR). A delocalized‐state transition is clearly observed in PR spectra while several localized‐state emission lines due to isoelectronic centers appear in photoluminescence spectra. The energy of optical transitions observed in PR spectra is in agreement with the excitonic transition energy in photoluminescence excitation spectra, clearly showing that the optical transitions in PR spectra are excitonic transitions. We analyzed the temperature dependence of the excitonic transition energies using the Bose–Einstein statistical expression, and found that even dilute alloys follow the same trend as GaAsN alloys with higher nitrogen concentrations. We discuss the coexistence of localized and delocalized states in dilute GaAsN alloys in terms of the random distribution of N atoms.

First‐principles study on the conduction band electron states of GaAsN alloys

AbstractWe have analyzed the electronic states of the lowest conduction band of GaAsN alloys based on the first‐principles calculation. In order to study the nitrogen concentration dependence of the electron effective mass, we calculated the electronic structure of GaAsN alloys using a full‐potential density functional theory program. The calculated effective mass of GaAsN with a dilute nitrogen concentration is about twice as heavy as that of GaAs. In addition, the effective mass is found to decrease with increasing nitrogen concentration although it is always heavier than that of GaAs. In addition, we calculated the density of states of GaAsN to examine what the cause of the decrease in the effective mass is. Our calculations suggest the discontinuity of the physical property from GaAs to GaAsN and provide an important insight into the formation of the conduction band states of GaAsN alloys. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)