Local vibrational properties of gaas studied by extended x

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Micro-Raman measurements have been carried out using and nm lines of diode lasers, and the nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements.

Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples.

Line shapes of the Raman scattering spectrum with the and nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the nm line has exhibited only vibrational modes.

As a complementary tool of Raman scattering measurements with the excitation source of nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. Raman spectroscopy has been a useful instrumental tool for characterization of semiconductors in terms of crystal quality, strain-induced effects, impurity modes and phonon energies[ 12 ]. Recently, it has been shown that Raman spectroscopy is also a powerful method to determine carrier effective mass and carrier concentration of doped semiconductors by analysing the line shape of LO-plasmon coupled modes[ 3 ].

Raman scattering is based on the inelastic scattering process of monochromatic light and mainly gives valuable information about vibrational normal modes.

The energy of excitation source in conventional Raman spectroscopy is much higher than the phonon energies; therefore, the process does not only involve electron—phonon interaction, but also creates electron—hole pairs via absorption and then annihilation of electron—hole pairs via recombination.

The radiative recombination process originating from transitions between electronic states can dominate the spectra and makes it impossible to resolve vibrational modes.

Therefore, in Raman spectroscopy, selection of the excitation source is a crucial issue[ 1 ]. Raman and infrared absorption spectroscopies have also been widely used to probe the bond configuration of dilute nitride semiconductors[ 2 ].

The presence of N in a host III-V material restructures the conduction band of the host material, and this modification has been well explained using the interaction between the localized N level and the extended conduction band state of the host material in terms of the band anti-crossing model[ 4 ]. Even a small percentage of N causes a large redshift of the band gap; therefore, incorporation of N into the III-V lattice brings more flexibility to tailor the band gap of the material[ 5 ].

However, the optical quality of dilute nitrides is drastically affected by the presence of N. Post- or in situ thermal annealing has been used as an effective method to improve optical and crystal qualities, but this process is responsible for a significant blueshift of the band gap energy[ 67 ].

The reason of the blueshift has been theoretically explained with the considerations of re-arrangement of the nearest neighbour configuration of the N environment[ 8 ] and re-shaping of quantum well QW from a square to a parabolic-like shape due to Ga-In interdiffusion[ 6 ]. Raman and infrared IR absorption spectroscopies have been used as experimental tools to confirm the theory[ 2 ]. In this work, we present the Raman scattering spectroscopy carried out with different laser linesand nm in order to reveal the importance of the excitation source energy on the nature of the Raman scattering line shape as electronic, vibrational or both.

The results obtained with the and nm excitation sources showed that when the energy of the excitation source is close to the electronic band gap energy of any constituent semiconductor material in the sample, a broad peak, which was supposed to stem from the electronic transitions, dominated the spectrum, making it impossible to resolve vibrational modes of respective semiconductors.

A comparison between the results of Raman and PL spectroscopies supported our interpretation of Raman scattering spectroscopy. Both techniques followed the same trend under different N concentrations and thermal annealing process. However, the intensity of the vibration modes has been observed to be very weak due to the multi-layered structure of the samples.

In order to analyse the effect of the N amount and thermal annealing on vibrational modes, attenuated total reflectance ATR IR absorption method is preferred as a complement to the micro-Raman scattering results.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. Dilute nitride III—V semiconductor alloys in thin films with variable bandgap have been on the extensively studied material systems [ 1 — 10 ] for optical telecommunications applications. Introduction of very low nitrogen concentrations is sufficient to modulate the band gap of such systems over a wide range. Amongst the possible III—V-based dilute nitride materials, GaAsSbN systems in the thin film configuration have been proven to be one of the promising systems for the spectral window of 1.

Simultaneous reduction in the band gap with lattice parameter and also independent tuning of conduction and valence band offsets by the N and Sb constituents, respectively, are the distinguishing features of this system. However, large disparity in the atomic radius of N and Sb creates N-induced defects and compositional disorder leading to non-radiative recombination centers, which adversely affect the optoelectronic properties of the thin film.

It is well established that considerable improvement in the optical properties occurs on annealing due to the annihilation of N-related centers. Reducing dimensionality further to nanowires, for example, may prove to be advantageous for this system in terms of efficient annihilation of point defects and enhanced photon collection due to the large surface to volume ratio. However, little work has been reported on dilute nitride GaAsSbN nanowires due to the complexities involved in growth of quaternary alloy nanowires.

These nanowires exhibited planar defects in addition to point defects, which is in contrast to thin films where only the latter dominates [ 12 ]. Thus, it is necessary to investigate the effect of defects and annealing on dilute nitride nanowires to understand and improve the optical properties. Temperature dependent PL was examined to understand the effects of localized states and recombination mechanisms. A constant Sb BEP of 1. Detailed growth procedures and characterization techniques are provided in our previous reports [ 111314 ].

To avoid possible short circuits at the sample edges, the top contacts were deposited using a shadow mask consisting of an array of 1-mm-diameter circular apertures to produce discrete contact pads. Then, a contact on the bottom of the substrate was deposited by electron beam evaporation. Electrical measurements were performed at room temperature using a Keithley characterization system by a two-probe method. The existence of twins and stacking faults in these nanowires indicate that annealing does not affect the planar defects present in the as-grown nanowires as described in an earlier publication [ 11 ].

This observation is not surprising as it is well known that annealing dilute nitride thin films primarily annihilates N-related point defects. Contributors to band tail-induced states include compositional fluctuations, localized defect states, and inhomogeneous lattice deformation [ 17 ].

With increasing annealing temperature, the intensity of band to band emission increases by fivefold with a corresponding decrease in the full width at half maxima FWHM of the PL peak while the intensity of the N-related defect peak at 0. These are typical signatures for annihilation of N-related defects, which results from significant reduction in the density of recombination centers responsible for non-radiative processes as in thin films.

Suppression of these non-radiative centers facilitates PL emission from higher energy states, which leads to increased PL intensity [ 891618 ] with increasing annealing temperature. An emission peak at 0. In addition, evolution of a distinct PL peak at 1. Temperature dependence of PL emission was studied for all samples, as shown in Fig.

This behavior is attributed to exciton localization in band tail states [ 19 — 22 ] due to potential fluctuations. This has been commonly explained in dilute nitride thin films [ 1623 ] as follows. In the low-temperature regime, with rising temperature, the excitons confined in the local potential minimum obtain sufficient thermal energy to surmount small barriers and thus relaxing to lower energy states.

The recombination of these excitons is responsible for the reduced PL emission energy causing an initial red shift. With further increase in temperature, the excitons gain sufficient energy to populate the higher energy band tail states, and the recombination from these states is responsible for the observed blue shift in the band gap. Beyond this temperature, free carrier recombination dominates, and the regular temperature-induced band gap shrinkage occurs due to the electron-phonon interaction and lattice relaxation.

Such an additional feature is normally reported to be due to splitting of the heavy hole HH and light hole LH leading to the corresponding excitonic transitions [ 24 ].

However, the PL spectra shown in Fig.Micro-Raman measurements have been carried out using and nm lines of diode lasers, and the nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak.

local vibrational properties of gaas studied by extended x

In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the and nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements.

On the other hand, Raman scattering spectrum with the nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out.

Raman spectroscopy has been a useful instrumental tool for characterization of semiconductors in terms of crystal quality, strain-induced effects, impurity modes and phonon energies [ 12 ]. Recently, it has been shown that Raman spectroscopy is also a powerful method to determine carrier effective mass and carrier concentration of doped semiconductors by analysing the line shape of LO-plasmon coupled modes [ 3 ].

Raman scattering is based on the inelastic scattering process of monochromatic light and mainly gives valuable information about vibrational normal modes. The energy of excitation source in conventional Raman spectroscopy is much higher than the phonon energies; therefore, the process does not only involve electron—phonon interaction, but also creates electron—hole pairs via absorption and then annihilation of electron—hole pairs via recombination.

The radiative recombination process originating from transitions between electronic states can dominate the spectra and makes it impossible to resolve vibrational modes. Therefore, in Raman spectroscopy, selection of the excitation source is a crucial issue [ 1 ]. Raman and infrared absorption spectroscopies have also been widely used to probe the bond configuration of dilute nitride semiconductors [ 2 ].

The presence of N in a host III-V material restructures the conduction band of the host material, and this modification has been well explained using the interaction between the localized N level and the extended conduction band state of the host material in terms of the band anti-crossing model [ 4 ]. Even a small percentage of N causes a large redshift of the band gap; therefore, incorporation of N into the III-V lattice brings more flexibility to tailor the band gap of the material [ 5 ].

However, the optical quality of dilute nitrides is drastically affected by the presence of N. Post- or in situ thermal annealing has been used as an effective method to improve optical and crystal qualities, but this process is responsible for a significant blueshift of the band gap energy [ 67 ].

The reason of the blueshift has been theoretically explained with the considerations of re-arrangement of the nearest neighbour configuration of the N environment [ 8 ] and re-shaping of quantum well QW from a square to a parabolic-like shape due to Ga-In interdiffusion [ 6 ]. Raman and infrared IR absorption spectroscopies have been used as experimental tools to confirm the theory [ 2 ]. In this work, we present the Raman scattering spectroscopy carried out with different laser linesand nm in order to reveal the importance of the excitation source energy on the nature of the Raman scattering line shape as electronic, vibrational or both.

The results obtained with the and nm excitation sources showed that when the energy of the excitation source is close to the electronic band gap energy of any constituent semiconductor material in the sample, a broad peak, which was supposed to stem from the electronic transitions, dominated the spectrum, making it impossible to resolve vibrational modes of respective semiconductors.

A comparison between the results of Raman and PL spectroscopies supported our interpretation of Raman scattering spectroscopy.The main and secondary features in the XANES show that there are differences in the average local Eu environment for the SnO 2 :Eu isolated thin films and heterostructures, being more organized in the latter.

Electrical characterization evidences that the portion of the resistivity reduction that corresponds to photo-ionized intrabandgap states is responsible for the persistent photoconductivity phenomenon in the heterostructures. There is currently great interest in semiconductor oxides and their heterostructures due to their potential applications in spintronic devices [ 1 ], photocatalysis [ 2 ], light-emitting diodes, lasers [ 3 ] and solar cells [ 4 ].

Tin dioxide SnO 2 is one of the most used semiconductor oxides, related to outstanding properties such as high transparency in the visible range, high reflectivity in the infrared [ 5 ] and high n-type free carrier concentration [ 6 ], even in the undoped form, which may lead to a high conductivity when electron scattering phenomena are prevented.

Doped SnO 2 thin films are used as transparent electrodes in several systems: perovskite solar cells [ 7 ], lithium-ion batteries [ 8 ] and organic photovoltaic cells [ 9 ]. The interest in doping semiconductor oxides with rare-earth RE ions has increased considerably, due to its radiative emissions over a large wavelength range, which allows several types of applications such as LEDs, displays, telecommunications, analytical sensors and biomedical images [ 10 ].

Its properties depend on the location of the rare-earth ion incorporation within the crystalline lattice of the matrix [ 11 ]. Grzeta and coworkers [ 15 ] have determined the oxidation state of Eu doping and the coordination within the BaAl 2 O 4 host structure. The coexistence of europium doping divalent and trivalent ions in Ga 2 O 3 nanocrystals was demonstrated by Layek and coworkers [ 16 ].

The Eu valence increases with pressure and Ca concentration, agreeing with f - d hybridization in determination of the electronic structure; besides, it changes almost linearly with applied pressure. The chemical pressure exerts a very weak influence on the Eu valence compared with the external pressurewhich leads to EuCo 2 As 2 crystal lattice softness. Rare-earth doping presents high quantum efficiency on the photoluminescence PL when incorporated into wide bandgap semiconductors [ 18 ].

However, they affect significantly the electrical transport in oxide semiconductor due to the acceptor-like behavior. Moreover, photo-induced current decay data for different temperatures, excited with below and above SnO 2 -bandgap light energies, reveal the possible confinement of electrons at the heterostructure interface region and that the persistent photoconductivity PPC phenomenon comes from intrabandgap states in the SnO 2 top layer [ 2526 ], which presents typically local lattice relaxation.

Moreover, in SnO 2several sorts of PL emission may be present related to the matrix itself. As can be seen, the broader band is clearly present in our data and is highly dependent on the thermal annealing temperature. The origin of this band has been the issue of another publication [ 20 ], and it will not be treated here.

local vibrational properties of gaas studied by extended x

Thin films of gallium arsenide were resistively evaporated using an Edwards AUTO evaporator system. The film growth is done at room temperature and air atmospheric conditions. This procedure is repeated 10 times for the formation of a layer deposited sample. Another sample is also done with the remaining powder of SnO 2 :2at.

Then, they were cleaned with ethyl alcohol to remove any impurity from the surface.Calculated total magnetic moment for the unit cell within the magnetic ordering provided see below. Typically accurate to the second digit. Calculated formation energy from the elements normalized to per atom in the unit cell. Stability is tested against all potential chemical combinations that result in the material's composition.

In general, band gaps computed with common exchange-correlation functionals such as the LDA and GGA are severely underestimated. We additionally find that several known insulators are predicted to be metallic. Persson, Geoffroy Hautier, Gian-Marco Rignanese, High-throughput density functional perturbation theory phonons for inorganic materials, Scientific Data doi Documentation Visualization: Henrique P.

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Miranda and Ludger Writz in preparation phononwebsite. Select an element to display a spectrum averaged over all sites of that element in the structure. Download spectra for every symmetrically equivalent absorption site in the structure. Explore more synthesis descriptions for materials of composition GaAs. Text computed by synthesisproject. Note the primitive cell may appear less symmetric than the conventional cell representation see "Structure Type" selector below the 3d structure.

These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. Material Details Final Magnetic Moment 0. Density 5.

Band Structure and Density of States. Semi-local DFT tends to severely underestimate bandgaps. Please see the wiki for more info.Extended X-ray absorption fine structure EXAFS has been measured at both the K edges of gallium and arsenic in GaAs, from 14 to K, to investigate the local vibrational and thermodynamic behaviour in terms of bond expansion, parallel, and perpendicular mean square relative displacements and third cumulant.

The separate analysis of the two edges allows a self-consistent check of the results and suggests that a residual influence of Ga EXAFS at the As edge cannot be excluded.

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The relation between bond expansion, lattice expansion, and expansion due to anharmonicity of the effective potential is quantitatively clarified. The comparison with previous EXAFS results on other crystals with the diamond or zincblende structure shows that the values of a number of parameters determined from EXAFS are clearly correlated with the fractional ionicity and with the strength and temperature interval of the lattice negative expansion.

Abstract Extended X-ray absorption fine structure EXAFS has been measured at both the K edges of gallium and arsenic in GaAs, from 14 to K, to investigate the local vibrational and thermodynamic behaviour in terms of bond expansion, parallel, and perpendicular mean square relative displacements and third cumulant.These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily.

Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online.

local vibrational properties of gaas studied by extended x

Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. First-principles FP calculations of the electronic and vibrational properties of three different Haeckelite structures have been performed. The relatively low cohesive energies when compared to C 60 of these phases suggest the possible synthesis of such novel carbon arrangements.

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In agreement with previous tight-binding calculations Terrones, H. In addition, within the ab initio framework, we predict the IR and Raman frequencies, which constitute the fingerprint of their structure and allow for their unambiguous identification.

STM images and quantum conductances of various tubular Haeckelite structures are also calculated within a tight-binding framework. The three investigated Haeckelite structures are shown to be good candidates of conducting wires with great potential in nanoelectronics. The results presented here provide a catalog of properties that will aid in the identification of other Haeckelite structures as well as carbon systems containing pentagonal and heptagonal defects.

View Author Information. Cite this: Nano Letters45— Article Views Altmetric. Citations Cited By. This article is cited by 51 publications. The Journal of Physical Chemistry C51 Journal of the American Chemical Society17 Journal of the American Chemical Society46 ACS Nano3 11 Nano Letters7 12 Peeters, Biplab Sanyal.

PAI-graphene: A new topological semimetallic two-dimensional carbon allotrope with highly tunable anisotropic Dirac cones. Carbon, Talla, Arwa F.


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