Search

The integrated intensity of X-ray diffraction reflections has been measured for a series of epitaxial layers of AIII nitrides (GaN, AlN, AlGaN) grown on different substrates (sapphire, SiC) and characterized by different degrees of structural perfection. It has been shown that, despite a high density of dislocations and a significant broadening of the diffraction peaks, the obtained values are not described by the kinematic theory of X-ray diffraction and suggest the existence of extinction. The results have been analyzed on the basis of the Darwin and Zachariasen extinction models. The secondary extinction coefficients and the thicknesses of epitaxial layers have been determined using two orders of reflection both in the Bragg geometry (0002 and 0004) and in the Laue geometry (\(10\bar 10\)) and \(10\bar 20\)). It has been demonstrated that the secondary extinction coefficient is the greater, the smaller is the broadening of the diffraction peaks and, consequently, the dislocation density. It has been found that, for epitaxial layers with a regular system of threading dislocations, the secondary extinction coefficient for the Laue reflections is substantially greater than that for the Bragg reflections.

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al2O3 substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10−2) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.

The three-wave diffraction in epitaxial layers of an AlxGa1 − xN solid solution has been measured using the Renninger scheme. From a comparison with similar diagrams measured earlier for GaN and AlN layers, it follows that the curves for the solid solution have a significantly higher intensity in the range of azimuthal angles outside the three-wave peaks. This indicates the existence of the two-wave Bragg reflection 0001 forbidden for wurtzite structures. It has been shown that the appearance of this reflection is due to a partial ordering of the solid solution in AlxGa1 − xN layers. From the measured structure factor F(0001) of the layers with various Al concentrations, it follows that the degree of ordering (an Al excess in one cation AlGa plane and an Al deficit in another plane) of the given series of samples is almost independent of the solid solution layer composition.

Three-beam X-ray diffraction (XRD) has been measured using the Renninger scheme in epitaxial ZnO layers with various thicknesses and degrees of crystal perfection. The integral intensity of three-beam XRD reflections has been analyzed and compared to that of two-beam reflections in the Bragg and Laue geometry. It is established that, for thin ZnO layers grown in the presence of excess oxygen, the integral intensity of three-beam diffraction peaks and Laue reflections is much smaller than that for layers of the same thickness grown in the presence of excess zinc. This fact is explained by the formation of a textured sublayer in the former case.

The Alx Ga1–xN layers with a wide range of AlN molar fraction (0 < x < 0.6) were grown by ammonia MBE on (0001)-oriented sapphire substrates using silane as the silicon dopant. The structural, electrical and optical properties of the layers were investigated by atomic force microscopy, X-ray diffraction, Hall, Raman, photoluminescence and cathodoluminescence measurements. It was found that doping affects surface morphology, dislocation density and luminescence intensity of the Alx Ga1–xN layers. A sharp decrease of the luminescence intensity for the heavily doped GaN and Al0.3Ga0.7N layers was explained by enhancement of the nonradiative recombination rate in degenerate GaN layers and by an increase in the defect concentration in AlGaN layers. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray multiple diffraction in epitaxial films of III-nitrides has been studied. A series of single layers of GaN, AlN, AlGaN and superlattices AlGaN/GaN of different thickness and structural perfection grown on c-sapphire are under study. Renninger scans for a primary forbidden 0001 reflection was used. The three beam diffraction peaks were measured in both φ-scans and θ-scans and their FWHM was analyzed. In the Renninger pattern all the possible 10 multiple peaks in an angular range (0–30)° are observed. It is shown that the FWHM of the φ-peaks reflects a crystalline perfection level but does not depend markedly on the multiple combination type. The angular width of the θ-scan peaks also increases with increasing of dislocation density and strongly depends on the type of three-wave reflection. The combinations with pure Laue secondary reflection (1–100)/(–1101), (3–1–20)/(–3121) and (3–2–10)/(–3211) are most sensi-tive to the dislocations. Most narrow peaks for the samples with the large dislocation density take place for the multiple combination (01–13)/(0–11–2) with the largest Bragg component of the diffraction vector. For the superlattices, θ–2θ-scan curve measured in the multiple position on the φ-scale contains satellites with angular distance corresponding to the forbidden 0001 reflection. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Three-beam X-ray diffraction in AlGaN/GaN superlattices (SLs) grown by metalorganic chemical vapor deposition on c-sapphire has been measured in the Renninger scheme. The primary beam corresponds to a forbidden 0001 reflection. Then, θ-scan curves were measured at the maximum of each three-beam diffraction peak. The average parameters a and c of SLs have been determined using the angular positions of three-beam diffraction peaks on the Renninger diagram (φ-scan curves). It is shown that a diffraction pattern with satellites on the θ-2θ curve of 0001 reflection can be obtained in the azimuthal position of three-beam diffraction. The angular widths of three-beam diffraction peaks measured in both φ and θ scans have been analyzed as related to the defect structure of layers. On this basis, a new method of determining the structural parameters of SLs is proposed.

Three-wave diffraction of X-rays is measured using the Renninger scheme for a series of GaN epitaxial layers of various thicknesses and degrees of structural perfection. In each 30°-angular interval of azimuthal rotation, all ten three-wave peaks determined by the geometry of diffraction with the 0001 first forbidden reflection and CuKα radiation are observed. The φ- and θ-scanned diffraction curves are measured for each three-wave combination. The angular FWHM of the diffraction peaks formed in experiments and its relation with the parameters of the two-wave diffraction pattern and the dislocation structure of the layers are analyzed. It is shown that the φ-scan peaks are less sensitive to the degree of structural perfection than the γ-mode peaks. The strongest dependence on the dislocation density for the latter peaks is observed for the \((1\bar 100)/(\bar 1101)\) and \((3\bar 2\bar 10)/(\bar 3211)\) three-wave combinations with a pure Laue component of secondary radiation, while the \((01\bar 13)/(0\bar 11\bar 2)\) combination with a large Bragg component exhibits the weakest dependence. Splitting of three-wave Renninger peaks associated with the coarse-block structure of some of the layers with rotations of the blocks about the normal to the surface is detected. The total integrated intensity of all three-wave combinations is determined and their ratios are in qualitative agreement with the theory.

Using Si(As, P, B) and GaSb(Si) study, possibilities of X-ray diffraction methods for diagnostics of highly doped semiconductor crystals in characterization of dopant state - whether it is in the crystals in the form of solid solution or under various stages of its decomposition - are shown. The combination of techniques of X-ray diffraction topography and high resolution X-ray diffractometry, higher sensitive to the crystal lattice strain than that traditionally used is taken as the basis for investigating the crystals with slight and strong absorption of X-rays. These methods were supplemented with digital processing of the topographic images of growth striations and electrical measurements.

X-ray multiple diffraction in epitaxial films of GaN with various densities of dislocations has been measured using Renninger scans for a primary forbidden (0001) reflection. The angular widths of three-beam diffraction peaks measured in both φ scans (rotation about the normal to the sample surface) and θ scans (rotation about the Bragg angle) have been analyzed. It is established that the three-beam Renninger diffraction peaks exhibit splitting due to a large-block structure of epilayers. For some three-beam combinations, the half-width (FWHM) of θ scan peaks is highly sensitive to the dislocation density.

Si(As, P, B) and GaSb(Si) single crystals are used as examples to demonstrate the possibilities of methods of X-ray diffraction for the diagnostics (examination of a real structure) of highly doped semiconductor crystals. Prominence is given to characterizing the state of impurity: whether it is in a solid solution or at a certain stage of its decomposition. An optimum combination of X-ray diffraction methods is found to obtain the most complete information on the microsegregation and structural heterogeneity in crystals with low and high X-ray absorption. This combination is based on X-ray diffraction topography and X-ray diffractometry methods having an increased sensitivity to lattice strains.

The structure perfection in two samples of the InN-GaN bilayer heterosystem, grown by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) on (0001)-oriented sapphire substrates, has been studied by the X-Ray diffraction techniques. Components of the microdistortion tensor were determined from an analysis of the broadening of diffraction peaks measured in various geometries. These data were used to evaluate the densities of various dislocation families in each layer of the heterosystem and to trace a change in the dislocated structure from the lower (GaN) to upper (InN) layer. A difference in the behavior of dislocations in the two samples grown by different methods (MBE versus MOVPE) suggests that different mechanisms of relaxation of the elastic stresses between InN and GaN layers are operative in these cases.

The structural state of GaN epitaxial layers grown on r-plane sapphire through metal-organic vapor phase epitaxy has been investigated using X-ray diffraction. The interplanar spacings in two directions in the (11\( \bar 2 \)0) plane of the interface and in the direction perpendicular to it, as well as the diffraction peaks in the ϑ and ϑ-2ϑ scan modes in the Bragg and Laue geometries, are measured on double- and triple-crystal diffractometers. The intensity distribution maps for asymmetric Bragg reflections are constructed for two azimuthal positions of the sample. An analysis of the data obtained has demonstrated that the elastic strain is anisotropic and that the X-ray diffraction pattern parallel to the interface plane is broadened. The layers are contracted in the [1\( \bar 1 \)00] direction and unstrained in the [0001] direction. The broadening of the Bragg reflections in the [1\( \bar 1 \)00] direction is considerably larger than that in the [0001] direction. It is shown using the Williamson-Hall plots for the Bragg and Laue reflections that these broadenings are not related to different degrees of mosaicity but are determined by the local dilatations and misorientations around defects. The data obtained are analyzed, and the conclusions regarding the dislocation structure of the samples are drawn.

Multilayer structures based on the InxGa1 − xN/GaN compounds grown by gas-phase epitaxy from organometallic compounds are studied using photoluminescence spectroscopy and high-resolution X-ray diffraction. A method for analyzing the experimental rocking curves of multilayer structures in terms of the Parratt-Speriosu model is developed. This method permits one to determine the thickness, period, and average composition of InxGa1 − xN/GaN layers, as well as the deformation of the active region in the samples under study. The local indium content is determined using the theoretical model which describes the radiation energy as a function of the thicknesses of the InGaN layers taking into account the energy of quantum confinement, the energies of the spontaneous polarization and piezoelectric polarization, and the parameters determined from high-resolution X-ray diffraction data.

It is shown that effective diagnostics of strongly doped Czochralski-grown silicon single crystals in the initial (as-grown) state is provided by methods based on the interference phenomena of dynamic x-ray diffraction: the Lang section topography and the Borrmann effect diffractometry. The conditions of a test for the structural perfection of as-grown crystals, based on the observation of interference bands on the section topographs, are refined.

The defect structure of AlGaN/GaN superlattices and GaN layers grown through vapor-phase epitaxy from organometallic compounds is investigated using x-ray diffraction analysis before and after implantation with erbium ions at an energy of 1 MeV and a dose of 3 × 1015 cm−2, as well as after annealing. For a superlattice with a total thickness larger than the implantation depth, the satellites of the superlattice region strained under the action of ions disappear in the x-ray diffraction pattern after annealing at temperatures higher than 900°C. This suggests that the radiation-induced defects responsible for the positive deformation in the layer are annealed at these temperatures. However, annealing even at a temperature of 1050°C does not lead to complete recovery of the initial state and the positive deformation in the remaining regions is caused by residual defects. An analysis of the x-ray diffraction patterns demonstrates that, in samples with thin superlattices located at the depth corresponding to maximum radiation damage, the periodic structure that disappears after implantation at a dose of 3 × 1015 cm−2 is not recovered even after annealing at a temperature of 1050°C. This inference is confirmed by the results of examinations with an electron microscope.

High-resolution x-ray diffractometry and electron microscopy are used to study the defect structure and relaxation mechanism of elastic stresses in AlGaN/GaN superlattices grown by the MOCVD method on sapphire covered with a preliminarily deposited GaN and AlGaN buffer layer. Based on an analysis of the half-widths of three-crystal scan modes of x-ray reflections measured in different diffraction geometries, the density of different dislocation families is determined. For all the dislocation families, the density is shown to increase with the Al concentration in the solid-solution layers and depend only weakly on the superlattice period. From the electron-microscopic patterns of planar and cross sections, the types of dislocations and their distribution in depth are determined. It is shown that, in addition to high-density vertical edge and screw dislocations, which nucleate in the buffer layer and propagate through the superlattice layers, there are sloped intergrowing dislocations with a large horizontal projection and bent mixed dislocations with a Burgers vector $$\left\langle {11\overline 2 3} \right\rangle $$ at the interface between individual superlattice layers. The former dislocations form at the interface between the buffer layer and the superlattice and remove misfit stresses between the buffer and the superlattice as a whole, and the latter dislocations favor partial relaxation of stresses between individual superlattice layers. In samples with a high Al concentration (greater than 0.4) in AlGaN layers, there are cracks surrounded by high-density chaotic horizontal dislocations.

Paper presents an overview of recent results on novel CdSe quantum dot (QD) fabrication techniques with the main impact on a stressor-controlled self-organization process resulting in nucleation of real CdSe QDs optically active up to room temperature, with a narrower size distribution, a higher density and a high Cd content. The main idea of the stressor-controlled epitaxy is an intentional introduction of a super-strained fractional monolayer of the much higher lattice-mismatch compound - stressor - to create strong local stress fields on the growth surface which govern self-assembling of the main QD material. The studies are performed on a type-II non-common atom CdSe/BeTe system, where CdTe (Δa/a ∼ +14%) and BeSe (Δa/a ∼ -10%) interface bonds play a role of intrinsic stressors. Both experimental data (growth, structural and optical characterization) and Monte Carlo simulation of the growth process are presented.

Three-crystal x-ray diffractometry is used for structural studies of nitride AlGaN/GaN superlattices (SLs) grown by metal-organic chemical vapor deposition on sapphire with GaN and AlGaN buffer layers with widely varied SL period (from 50 to 3500 A), Al content in Alx Ga1−x N layers (0.1≤x≤0.5), and buffer layer composition. Satellite peaks characteristic of SLs are well pronounced up to the third order in θ-2θ scans of symmetric Bragg reflections and θ scans of the symmetric Laue geometry. The corresponding curves are well modeled by kinematic formulas. The average SL parameters, as well as the thickness, composition, and strain of individual layers, are determined using a combination of symmetric Bragg and Laue reflections. It is shown that all the samples under study are partially relaxed structures in which the elastic stresses between the entire SL and the buffer layer, as well as between individual layers, are relaxed. The AlGaN layers are stretched and the GaN layers are compressed. The GaN layer compression is larger in magnitude than the AlGaN layer tension because of thermoelastic stresses.

Molecular beam epitaxy was used for the first time to grow novel GaAs/GaSb heterostructures with ultrathin (0.8–3 monolayers) GaAs layers embedded in GaSb. These structures were studied by X-ray diffraction, transmission electron microscopy, and photoluminescence. By contrast to known structures with self-assembled quantum dots, GaAs layers in GaAs/GaSb structures are subject to elastic tensile stresses due to 7% lattice mismatch. The structures exhibit intense photoluminescence in the 2 µm region at low temperatures. Quantum-dimensional islands are formed in the structure at a nominal GaAs layer thickness exceeding 1.5 monolayers. The band alignment of the structures is of type II.

The X-Ray diffraction (XRD) reflections from epitaxial layers with various microstructures have been measured in the Bragg and Laue geometries. The shapes of XRD peaks measured in the θ and θ–2θ scan modes have been analyzed using the approximation by the Voigt function. It is shown that, for the structures with more regular dislocation systems, the Gaussian component predominates, whereas a more chaotic distribution of dislocations leads to an increase in the Lorentzian component. Far on the wings of XRD peaks, the rate of intensity decrease exceeds that predicted by the Voigt function.

The dislocation structure of hydride vapour phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming large angles with the basal plane) with two modes of scanning (θ and θ-2θ) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaN films grown on sapphire without and with undoped and Si-doped metal-organic chemical vapour deposited templates.

The dislocation structure of hydride vapor phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming a large angle with the basal plane) with two modes of scanning (θ and θ–2θ) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaNfilmsgrown on sapphire with and without undoped and Si-doped metalorganic chemical vapor deposited templates. Transmission electron microscopy was used to confirm the x-ray results by direct visualization of defect rearrangements.

The method of two-and three-crystal x-ray diffractometry (TCD) is used for studying the dislocation structure of thick GaN layers grown by chloride gaseous-phase epitaxy (CGE) on sapphire, as well as on a thin GaN layer, which is grown by the metalloorganic synthesis (MOS) method. Five components of the microdistortion tensor 〈ɛij〉 and the sizes of the coherent scattering regions along the sample surface and along the normal to it are obtained from the measurements of diffracted intensity in the Bragg and Laue geometries. These quantities are used to analyze the type and geometry of the dislocation arrangement and to calculate the density of the main types of dislocations. The density of the vertical screw dislocations, as well as of the edge dislocations, decreases (by a factor of 1.5 to 3) during growth on a thin GaN layer. The diffraction parameters of the thick layer on the MOS-GaN substrate suggest that it has a monocrystalline structure with inclusions of microcrystalline regions.

We present studies of the excitonic spectrum in superlattices (SLs) of CdSe insertions in a ZnSe matrix aimed at elucidating the CdSe/ZnSe interface morphology. The experimental photoluminescence excitation spectra are compared with the results of variational exciton calculations performed within the effective mass approximation. The shape of the average vertical (along the SL growth axis) distribution of CdSe within each insertion, used in the calculations, was obtained from a theoretical simulation of X-ray diffraction (XRD) rocking curves measured in the same samples. The results indicate that the thinnest layers are graded composition ZnCdSe quantum wells (QWs), generally homogeneous in the layer planes, whereas flat islands enriched by Cd appear at the CdSe nominal thickness larger than 0.5-0.6 monolayer (ML).

New pseudomorphic superlattices (SLs) based on calcium and cadmium fluorides have been grown from molecular beams and structurally characterized by high-resolution X-ray diffractometry. It was found that positions of the CdF 2 and CaF 2 emission bands in the SLs with the shortest periods shifted to the blue and red parts of the optical spectra, respectively. It was revealed that the Eu 2+ luminescence intensity under continuous optical excitation drastically decreases in a few seconds after the beginning of the excitation. This effect was accounted for by the photoionization of Eu 2+ ions with charge transfer from their 4f 6 5d excited state to the neighbouring CdF 2 layers.

Two-and three-crystal diffractometric study of the structural perfection of GaN epitaxial films grown on sapphire, GaAs, and SiC substrates is reported. The diffraction intensity distributions around the reciprocal-lattice points are shown to be extended in the direction parallel to the surface, which is connected with the anisotropy of the local strain fields in the layers. A comprehensive analysis is made of the broadening for several reflection orders measured in three geometries, namely, Bragg, symmetric Laue, and grazing-angle diffraction. The five independent components of the microdistorsion tensor δe ij , as well as the average coherent-scattering lengths in two directions, τ z and τ x , have been obtained. It is shown that for most samples the components responsible for reflection broadening along the surface are noticeably larger, i.e. δe xx >δe zz , and δe zx >δe xz , as well as τ z >τ x . All tensor components are related to a specific dislocation type. Electron microscopy of the samples revealed a high density of pure edge and pure screw dislocations extending normal to the interface, and which provide a dominant contribution to e xx and e zx , respectively.

Short-period superlattices (SL) with periods from 7 to 22 nm were grown by MBE in the CdF2-CaF2 system on Si(111). X-ray diffraction measurements of these structures in various reflection and transmission geometries demonstrate the possibility of producing such objects with a high crystal perfection. Specific features of diffraction from an SL with layers possessing substantially different diffracting abilities and strains of opposite signs with respect to the substrate are considered. The main parameters of the grown SLs have been obtained by simulation in semikinematic approximation. The applicability of the model of a perfect SL to objects with structural defects has been demonstrated.

Double-and triple-crystal diffractometry have been used to study structural perfection of a ∼1 µm-thick Ga1−xInxSb1−yAsy epitaxial film (x=0.9, y=0.8) on GaSb. It is shown that scattering from samples of this system can be divided into coherent and diffuse. The arrangement of reciprocal-lattice points of the film and substrate in the two-dimensional intensity distribution for asymmetrical reflections argues for the absence of elastic-strain relaxation. No dislocation networks are formed, and the diffuse scattering is produced by Coulomb-type defects. Localization of diffuse scattering in reciprocal space suggests that these defects reside in the epitaxial film. The diffuse-scattering distribution in asymmetrical reflections is shown to be anomalous; namely, it extends in a direction parallel to the surface and is split into two maxima. Schemes have been proposed and realized for measuring integral distributions of diffracted intensity along the surface and perpendicular to it, and their potential for studying diffuse scattering from defects is explored.

The paper presents the X-ray diffractometry analysis of thin-layer structures made by exploiting the combination of two diffraction geometries—the Bragg one and the Laue one. For this purpose a three-crystal setting was applied. Since the structural parameters of thin layers vary primarily along the surface normal, directing the diffraction vector along this normal, one can succeed in the assessment of the quality in whole, but not in the extraction of different components of lattice damage. The paper shows that, in order to evaluate the contributions, the application of the Laue geometry is promising; it substantially facilitates the study of relaxation, the determination of compositionally dependent properties and the evaluation of macro- as well as micro-strain components. The objects under study were GaAs/Si and SiGe/Si heterostructures as well as (CaF2+CdF2)/Si superlattices.

Growth of high quality wurtzite-structure GaN layers on (111) MgAl2O4 by gas source molecular beam epitaxy is described. Hydrazine was used as a source of active nitrogen. In situ reflection high energy electron diffraction was used to monitor the growth mode. Two-dimensional growth was obtained at temperatures above 750 °C on multi-step GaN buffer layers. The resulting GaN films show excellent luminescence properties.

X-ray diffraction measurements have been carried out on epitaxial superlattices (SLs) in symmetric Laue geometry. High quality pseudomorphic CdF2/CaF2 SLs on Si(111) have been used as samples. Satellites, due to periodic variations of structural factor value, are revealed at ω-scanning rocking curves. A comparison of information about SL provided by diffraction in Bragg and Laue geometries is presented. The possibility of direct determination of SL structural parameters is discussed.

New CdF/sub 2/-CaF/sub 2/:Eu superlattices (SLs) were grown from molecular beams and structurally characterized by high resolution X-ray diffractometry and high resolution transmission electron microscopy (HRTEM). A new optical phenomenon in luminescence of Eu/sup 2+/ ions in the SLs was revealed. It was found that the Eu/sup 2+/ luminescence intensity under continuous optical excitation drastically decreases in a few seconds after the beginning of the excitation. Possible application of the phenomenon in optical memory cells is discussed.

It is shown that such parameters of GaN/AlxGa1-xN superlattice as the period, build-in strain, composition of the alloy, and individual layer thicknesses can be extracted from the energy positions, intensities, and line shapes of various optical and acoustical modes detected in Raman scattering.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The photoluminescence spectra of samples of the solid solution In(0.5)Ga(0.5)P before and after implantation of high-energy nitrogen ions to doses of 1011−5×1012 cm−2 shows that the photoluminescence of the implanted (and annealed) samples may be the result of the formation of essentially one-dimensional semiconductor structures along the individual ion tracks.

It is shown that such parameters of GaN/Al x Ga 1-x N superlattice as the period, built-in strain, composition of the alloy, and individual layer thicknesses can be extracted from the energy positions, intensities, and line shapes of various optical and acoustic modes detected in Raman scattering.

The effects of the layer thickness and alloy composition on the Raman spectra of hexagonal GaN/Al x Ga 1-x N multilayer structures have been investigated. Our findings show that the A 1 (TO) optic mode can be regarded as propagating through the structure, whereas other optic modes are confined to the GaN or Al x Ga 1-x N layer. We report the first observation of folded acoustic modes in short-period GaN/Al x Ga 1-x N superlattices. The dispersion of the LA phonon branch was determined by using different Raman scattering configurations. The sound velocity for GaN/Al x Ga 1-x N SL with Al content x = 0.28 was found to be 8410 m/s.