Structural modifications of GaN after cerium implantation

Among the family of rare earth (RE) dopants, the doping of first member Ce into GaN is the least studied system. This article reports structure properties of Ce‐doped GaN realized by technique of ion implantation. Ce ions were implanted into metal organic chemical vapor deposition grown n‐ and p‐GaN/sapphire thin films at doses 3 × 10¹⁴ and 2 × 10¹⁵ cm⁻². X‐ray diffraction scans and Raman scattering measurements exhibited expansion of lattice in the implanted portion of the samples. First order Raman scattering spectra show appearance of several disorder‐activated Raman scattering modes in addition to typical GaN features. A dose‐dependent decrease in intensity of E₂ mode was observed in Raman the spectra of the implanted samples. Ultraviolet Raman spectra of implanted samples show complete quenching of photoluminescence emission and appearance of multiple A₁(LO) phonon scattering modes up to fifth order. Moreover, a decrease in intensity and an increase in line width of LO modes as a function of wavenumber were observed for implanted samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation of weak damage in Al0.25Ga0.75As/GaAs by using RBS/C and Raman spectroscopy

The weak damage induced by 0.8 MeV Si ion implantation in the Al_0.25Ga_0.75As films epitaxially grown on GaAs substrates was studied by using Rutherford backscattering spectrometry/channeling (RBS/C) and Raman spectroscopy. RBS/C spectra measured from the implanted samples showed rather low damage level induced by the ion implantation with ion dose from 1×10¹⁴ to 5×10¹⁵ cm⁻². The Raman spectra were measured on these samples. Two kinds of phonon modes, GaAs-like and AlAs-like, are observed, which indicate the existence of multiple phonon vibrational modes in the epitaxial Al_0.25Ga_0.75As films on the GaAs substrate. Compared with the unimplanted sample, the Raman photon peaks for the implanted sample shift gradually to lower energy with the increase of the implantation dose. The strains induced in the implanted layer were also evaluated from the Raman spectra. The result from high resolution double crystal X-ray diffractometry (HRXRD) also verified the evolution of the strains in the implanted layers.     

Photoluminescence studies of ZnO thin films on R-plane sapphire substrates grown by sol–gel method

Zinc oxide (ZnO) thin films on R-plane sapphire substrates were grown by the sol–gel spin-coating method. The optical properties of the ZnO thin films were investigated using photoluminescence. In the UV range, the asymmetric near-band-edge emission was observed at 300 K, which consisted of two emissions at 3.338 and 3.279 eV. Eight peaks at 3.418, 3.402, 3.360, 3.288, 3.216, 3.145, 3.074, and 3.004 eV, which respectively correspond to the free exciton (FX), bound exciton, transverse optical (TO) phonon replica of FX recombination, and first-order longitudinal optical phonon replica of FX and the TO (1LO+TO), 2LO+TO, 3LO+TO, 4LO+TO, and 5LO+TO, were obtained at 12 K. From the temperature-dependent PL, it was found that the emission peaks at 3.338 and 3.279 eV corresponded to the FX and TO, respectively. The activation energy of the FX and TO emission peaks was found to be about 39.3 and 28.9 meV, respectively. The values of the fitting parameters of Varshni's empirical equation were α=4×10^?3 eV/K and β=4.9×10³ K, and the S factor of the ZnO thin films was 0.658. With increasing temperature, the exciton radiative lifetime of the FX and TO emissions increased. The temperature-dependent variation of the exciton radiative lifetime for the TO emission was slightly higher than that for the FX emission.     

Morphological and micro-Raman investigations on Ar-ion irradiated nanostructured GaAs surface

Low energy Ar⁺-ion irradiation at normal incidence is used to fabricate nanostructured GaAs surface. Atomic force microscopy (AFM) images reveal the formation of GaAs surface nanodots with an average size of about 25-35 nm. The swelling of irradiated surface is observed at a higher energy due to the ion beam-induced porosity in the amorphized GaAs surface. Micro-Raman scattering shows a gradual increase in the downward shift and line shape broadening of optical phonon modes from the nanostructured GaAs prepared with increasing ion dose and beam energy. The rapid broadening of the transverse-optical phonon mode at a higher energy and dose represents the onset of plastic deformation of the irradiated surface. Furthermore, the influence of rapid thermal annealing (RTA) shows a reverse LO and TO phonon peakshift and the change in the lineshape due to reduction of the amorphous disorder.     

Au5+ ion implantation induced structural phase transitions probed through structural,microstructural and phonon properties in BiFeO3 ceramics,using synergistic ion beam energy

Implanted Au⁵⁺-ion-induced modification in structural and phonon properties of phase pure BiFeO₃ (BFO) ceramics prepared by sol–gel method was investigated. These BFO samples were implanted by 15.8?MeV ions of Au⁵⁺ at various ion fluence ranging from 1?×?10¹⁴ to 5?×?10¹⁵?ions/cm². Effect of Au⁵⁺ ions’ implantation is explained in terms of structural phase transition coupled with amorphization/recrystallization due to ion implantation probed through XRD, SEM, EDX and Raman spectroscopy. XRD patterns show broad diffuse contributions due to amorphization in implanted samples. SEM images show grains collapsing and mounds’ formation over the surface due to mass transport. The peaks of the Raman spectra were broadened and also the peak intensities were decreased for the samples irradiated with 15.8?MeV Au⁵⁺ ions at a fluence of 5?×?10¹⁵?ion/cm². The percentage increase/decrease in amorphization and recrystallization has been estimated from Raman and XRD data, which support the synergistic effects being operative due to comparable nuclear and electronic energy losses at 15.8?MeV Au⁵⁺ ion implantation. Effect of thermal treatment on implanted samples is also probed and discussed.     

First order Raman scattering analysis of transition metal ions implanted GaN

Transition Metal (TM) ions V, Cr, Mn and Co were implanted into GaN/sapphire films at fluences 5×10¹⁴, 5×10¹⁵ and 5×10¹⁶ cm⁻². First order Raman Scattering (RS) measurements were carried out to study the effects of ion implantation on the microstructure of the materials, which revealed the appearance of disorder and new phonon modes in the lattice. The variations in characteristic modes 1GaN i.e. E₂(high) and A₁(LO), observed for different implanted samples is discussed in detail. The intensity of nitrogen vacancy related vibrational modes appearing at 363 and 665 cm⁻¹ was observed for samples having different fluences. A gallium vacancy related mode observed at 277/281 cm⁻¹ for TM ions implanted at 5×10¹⁴ cm⁻² disappeared for all samples implanted with rest of fluences. The fluence dependent production of implantation induced disorder and substitution of TM ions on cationic sites is discussed, which is expected to provide necessary information for the potential use of these materials as diluted magnetic semiconductors in future spintronic devices.     

Exciton-phonon coupling in indirect gap AgBr nanocrystals

The resonance Raman scattering observed in the exciton region of indirect AgBr nanocrystals with mean particle radius R ≈ 5 nm is analyzed. Considering the processes as absorption followed by emission and calculating the size dependent exciton energies by the donor-like exciton model of Ekimov et al. [1], the 1TO(L) and 2TO(L)&LO(Γ) resonance behavior can be well-reproduced. The analysis of the Raman spectral lineshape based on linear exciton-phonon coupling shows a substantial increase of coupling strength with excitation photon energy. It is attributed to enhanced acoustic and surface phonon interaction of higher exciton states.     

Raman spectra in doped cadmium oxide

Raman spectra of polycrystalline CdO-samples with electron-densities between 0.8 × 10¹⁹ and 13 × 10¹⁹ cm^?3 and mobilities between 80 and 250 cm²V^?1sec^?1 were observed at 300 and 2 K. Two first order Raman peaks are found at 404 and 345 cm^?1 while the second order spectrum is interpreted as due to the following processes: 2LO(L) near 970 cm^?1, 2LO(X) near 780 cm^?1, 2TO(X) or 2TO(L) at 480 cm^?1 and TA + TO(X) at 270 cm^?1. The 2LO(L)-peak shift to lower energiesand broadens with increasing electron density. This effect cannot be explained by existing theories.     

Formation of InAs quantum dots in silicon by sequential ion implantation and flash lamp annealing

InAs quantum dots (QDs) were successfully formed in single-crystalline Si by sequential ion implantation and subsequent milliseconds range flash lamp annealing (FLA). Samples were characterized by μ-Raman spectroscopy, Rutherford Backscattering Spectrometry (RBS) high-resolution transmission electron microscopy (HRTEM) and low temperature photoluminescence (PL). The Raman spectrum shows two peaks at 215 and 235 cm^?1 corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs phonon modes, respectively. The PL band at around 1.3 μm originates from the InAs QDs with an average diameter 7.5±0.5 nm and corresponds to the increased band gap energy due to the strong quantum confinement size effect. The FLA of 20 ms is sufficient for InAs QDs formation. It also prevents the out-diffusion of implanted elements. Moreover, the silicon layer amorphized during ion implantation is recrystallized by solid-phase epitaxial regrowth during FLA.     

Waveguide effect in ZnO crystal by He+ ions implantation: Analysis of optical confinement from implant-induced lattice damage

Waveguide effect was observed in He⁺ implantation ZnO with different energies and doses. Computer code was used to simulate the process of ion implantation into ZnO crystal and the implantation-produced damage distribution is extracted according to RBS experimental result. The prism coupling and end-face coupling technique are used to investigate the waveguide properties. The reconstructed refractive index profile shows that the ordinary index decreases at the near surface region after He⁺ implantation under different conditions. The damage layer, which is governed by nuclear energy deposition of He⁺ ions, makes itself a reduced index barrier for guiding light. Ion-implantation, generally used for electrical isolation, may play a role for optical confinement in ZnO light emitting devices.     

离子注入ZnO薄膜的拉曼光谱研究

室温下,用80 keV N⁺和400 keV Xe⁺离子注入ZnO薄膜,注入剂量分别为5.0×10¹⁴—1.0×10¹⁷/cm²和2.0×10¹⁴—5.0×10¹⁵/cm².利用拉曼散射技术对注入前后的ZnO薄膜进行光谱测量和分析,研究了样品的拉曼光谱随离子注入剂量的变化规律.实验结果发现,未进行离子注入的样品在99,435 cm<     

Phonon dispersion in AgBr and exchange of the transverse mode Eigenvectors at L

Using inelastic neutron scattering, phonon dispersion curves for AgBr at 85 K are measured along the 〈100〉, 〈110〉 and 〈111〉 directions in reciprocal lattice. Special attention is payed to the anomalous behaviour of the TA and TO branches at the L-point (0.5; 0.5; 0.5). With high resolution (Δv = 0.24 THz) their frequencies are determined to be 1.54 and 1.93 THz, respectively. The ratio of their integrated intensities is found to be 2.15 ± 0.4. This value is in good agreement with the ratio of 2.38 calculated under the assumption that at L the heavier (Ag⁺) ions is vibrating with the higher and the lighter (Br^-) ion with the lower frequency, as suggested by recent lattice dynamical calculations. Comparison of our phonon frequencies with corresponding optical data prove that the momentum-conserving phonons associated with the lowest indirect exciton transition belong to the TO and LA phonon branches at L. Since the lowest conduction band minimum at Γ is well established experimentally, our results in turn imply that the uppermost valence band maximum is right at the L-point.     

Effect of Helium ion irradiation on the structure,the phase stability,and the microhardness of TiN,TiAlN, and TiAlYN nanostructured coatings

The radiation resistance of nanostructured TiN, TiAlN, and TiAlYN coatings is studied after 500-keV He⁺ ion irradiation in the fluence range 5 × 10¹⁶–3 × 10¹⁷ ions/cm². The radiation-induced changes in the phase composition, the structure, the lattice parameters, the morphology, and the mechanical properties of coatings are investigated. Blistering is found to be absent, and the radiation fluence is shown to affect the strength properties of the thin coatings nonlinearly. A significant decrease in the grain sizes is detected upon ion irradiation, which causes an increase in the microhardness and the radiation resistance of the coatings. The TiN, TiAlN, and TiAlYN coatings are found to be radiation-resistant coatings, which do not undergo serious degradation during high-fluence ion irradiation.     

2.5MeV的He+离子辐照316L不锈钢中氦泡的形核与生长研究

利用透射电子显微镜分析了0.3—0.5T_m温区（T_m为材料溶点）316L奥氏体不锈钢经高剂量氦离子辐照后辐照损伤峰区氦泡的形成行为.实验结果支持氦泡的双原子形核模型，并证实氦泡的形成主要受制于自间隙子/氦置换机制扩散.材料中高密度位错的存在显著增强氦泡形核并抑制氦泡生长.与前人低剂量辐照实验结果的比较表明0.3—0.5T_m温区氦泡形核机制不随辐照剂量或剂量率发生显著变化． 关键词：     

Effect of Cr implantation on structural and optical properties of AlN thin films

Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr⁺ ions for various dose from 10¹³ to 10¹⁵ cm⁻². The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E₂(high) and A₁(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr⁺-implanted AlN with a ion dose of 1×10¹⁵ cm⁻². Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose.     

Preferential sputtering of TIC under keV Ar+ ion bombardment: Simultaneous sputtering-ISS measurement with He+ and Ar+ ions

The composition change of the outermost atom layer of TiC(110) under ion bombardment with 1.5–3 keV He⁺ and He⁺ + Ar⁺ ions has been measured by ion scattering spectroscopy with He⁺ ions at different sample temperatures. It has been found that the preferential sputtering of C atoms takes place for both the He⁺ and Ar⁺ ion bombardment, however the preferred sputtering is more pronounced for Ar⁺ ions than for He⁺ ions. The ion bombardment with He⁺ ions at elevated sample temperatures hardly results in any change in surface composition below ～800°C, while Ar⁺ ion bombardment results in C enrichment for elevated temperatures as reported so far.     

Structural and Chemical Modification in a Polymer by Metal Ion Implantation

Physical and chemical properties changes in a polymer have been studied for polycarbonate (PC) implanted with 100 keV Ni⁺ ions with varying fluence from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². The changes in the surface morphology and composition have been observed with atomic force microscopy (AFM) and X-ray diffraction (XRD). The ions implanted induce changes in topography of PC and indicate that the roughness increases dramatically with ion fluence. Implanted metal ions shows direct evidence of compound formation on the surface. The chemical changes in the surface region have been carried out by Raman Spectroscopy and UV-VIS spectroscopy. UV-VIS absorption analysis indicates a drastic decline in optical band gap from 5.46 eV to 1.76 eV at an implanted dose of 1 × 10¹⁶ ions/cm². It could be shown that the partial destruction of chemical bonding under ion implantation leads to the creation of new amorphous and graphite-like structures, which is confirmed by Raman spectroscopy.     

Changes in Structural and Optical Properties of Polycarbonate Induced by Ag+ Ion Implantation

Transparent polycarbonate samples were implanted with 1 MeV Ag⁺ ions to various doses ranging from 5 × 10¹⁴ to 3 × 10¹⁶ ions cm^?2 with a beam current density of 900 nA cm^?2. Modification in the structure of polycarbonate as a function of the implantation fluence was investigated using micro-Raman spectroscopy, glancing angle X-ray diffraction, and UV-Vis spectroscopy. Raman spectroscopy pointed toward the formation of graphite structures/clusters due to the ion implantation. UV-Vis absorption analysis suggests the formation of a carbonaceous layer and a drastic decrease in optical band gap from 4.12 eV to 0.50 eV at an implanted dose of 3 × 10¹⁶ ions cm^?2. The correlation between the decrease in band gap and the structural changes is discussed.     

Large electric-field-induced enhancement of resonant Raman scattering of a single quantum well

The electric-field enhancement of the resonant Raman efficiency of confined optical phonon modes in a single quantum well has been observed in an asymmetrical n-type triple-barrier GaAs/AlAs resonant tunneling structure. The measurement takes advantage of an outgoing resonance with the e₂-hh₁ exciton transition confined to the wide quantum well, and according to the polarization properties, the Fröhlich interaction dominates the scattering mechanism. A fifteenfold increase is found from zero field to 7.5 × 10⁴ V/cm, which results from break-down of the parity selection rules for the photon-exciton and the exciton phonon coupling mechanisms.     

Soft modes and phonon interactions in studied by neutron scattering

The low frequency lattice dynamics and its relationship to the second order paraelectric-to-ferroelectric transition in Sn₂P₂S₆ is studied. The dispersion branches of the acoustic and lowest lying optical phonons in the a^*-c^* plane have been obtained in the ferroelectric phase, for x-polarized phonons. Close to the phase transition a considerable softening is found for the lowest optical mode (P_x), comparable to the behaviour observed in previous Raman investigations. As found previously in Sn₂P₂Se₆, a strong coupling between the TO(P_x) and TA(u_xz) phonons is observed, although, apparently, not strong enough to lead to an incommensurate phase. The soft TO(P_x) mode at the zone center is observed. The temperature dependence of its frequency and damping shows that the transition is not entirely displacive. At low temperatures an unusual apparent negative LO-TO splitting is observed which is shown to arise from the coupling of the x-polarized soft mode to the nearby z-polarized optical phonon. For comparison, the soft TO(P_x) dispersion in the a^*-b^* plane is measured in both the paraelectric and ferroelectric phases. Consistent frequency changes and LO-TO splitting are observed, revealing a significant interaction between the TA(u_yx) and LA(u_xx) acoustics branches and the TO and LO soft optic branches, respectively. In contrast, the nearby y-polarized optic branch shows almost no temperature dependence. Finally, the influence of piezoelectric effects on the limiting acoustic slopes in the ferroelectric phase is discussed. Received: 11 May 1998 / Revised and Accepted: 15 June 1998