Rutherford Backscattering Channeling Research Articles

Investigation of ZnO films on Si substrate grown by low energy O + assisted pulse laser deposited technology

Zinc oxide thin films (ZnO) with different thickness were prepared on Si (111) substrates using low energy O + assisted pulse laser deposition (PLD). The structural and morphological properties of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. The quality of ZnO films was also examined by using Rutherford backscattering spectroscopy/ion channeling (RBS/C) techniques. XRD showed that there was only one sharp diffraction peak at 2 θ = 34.3° with the full width at the half maximum (FWHM) of around 0.34° for two ZnO samples, which also indicated that ZnO thin films had a good c-axis preferred orientation. Results of Rutherford backscattering and ion channeling clearly indicated that the Zn:O ratio in zinc oxide thin film approached to unity and the ZnO thin film grown by low energy O + assisted pulse laser deposition had a polycrystalline structure. In the case of ZnO film fabricated by low energy O + assisted pulse laser deposited under identical experimental conditions except growth time, AFM analysis has shown that the root mean square (RMS) roughness (2.37 nm) of thinner ZnO film (35 nm) was far below that (13.45 nm) of the thicker ZnO film (72 nm).

Bismuth containing III–V quaternary alloy InGaAsBi grown by MBE

AbstractInGaAsBi epilayers were created on InP substrates by molecular beam epitaxy for the first time. The high crystalline quality of the InGaAsBi epilayer with smooth interface was confirmed by high resolution X‐ray diffraction measurements. Up to 2.5% Bi was incorporated in the film based on Rutherford back scattering (RBS) results. The RBS channeling spectra give clear evidence that the Bi atoms were substitutionally located in the InGaAs zinc‐blende lattice sites. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Groups III and V impurity solubilities in silicon due to laser, flash, and solid-phase-epitaxial-regrowth anneals

In this work the authors studied impurity solubilities of groups III and V elements in silicon resulting from laser anneal, flash anneal, and solid-phase-epitaxial regrowth. Rutherford backscattering channeling analysis was used to determine substitutional impurity depth profiles generated from the difference between the random and aligned spectra. Despite the large difference in peak temperatures and times, the anneals produce similar results with maximum solubilities beating the maximum equilibrium values by one to two orders of magnitude depending on the impurity. The correlation between the metastable solubility and the equilibrium distribution coefficient allows a prediction of values for other impurities not extracted experimentally.

Correlation of contact resistance with metal diffusion for oxidized Au/Ni/p-GaN contacts studied using Rutherford backscattering spectroscopy

The temperature- and time-dependent diffusion behaviours of oxidized Au/Ni/p-GaN ohmic contacts were studied with Rutherford backscattering spectroscopy/channelling (RBS/C). It was found that, after annealing at 450 °C, the Au diffused into the electrodes and contacted to the p-GaN and the O diffused into the electrodes to form NiO. Both of these processes are believed to be responsible for the sharp decrease in the specific contact resistance (ρc) at 450 °C. At 500 °C, the O diffused deeper into the interface. As a result, the ρc reached the lowest value at this temperature. The influence of the annealing time was also investigated. It was found that, at 500 °C, 1 min annealing caused obvious in-diffusion of Au and O and out-diffusion of Ni. The Au has even diffused into the p-GaN/metal interface. These diffusion behaviours are believed to cause the sharp decrease of ρc. Annealing for 5 min at 500 °C caused Au and Ni to in-diffuse and out-diffuse further, respectively. A longer annealing time, e.g. 10 min, only caused further in-diffusion of O. As for Au and Ni, no further in-diffusion and out-diffusion has been found for the samples annealed for 10 min at 500 °C. Therefore, the further decrease of ρc (5 × 10−4 Ω cm2) after 10 min annealing is attributed to the formation of more NiO at the interface. However, when the annealing temperature reached 600 °C, the ρc increases greatly. The reason for the increase of the ρc is also discussed.

Molecular Dynamics as a tool to interpret macroscopic amorphization-induced swelling in silicon carbide

We present here an investigation of the irradiation-induced swelling of SiC using Classical Molecular Dynamics simulations. Heavy ion irradiation has been assumed to affect the material in two steps: (a) creation of local atomic disorder, modeled by the introduction of extended amorphous areas with various sizes and shapes in a crystalline SiC sample at constant volume (b) induced swelling, determined through relaxation using Molecular Dynamics at constant pressure. This swelling has been computed as a function of the amorphous fraction introduced. Two different definitions of the amorphous fraction were introduced to enable meaningful comparisons of our calculations with experiments and elastic modeling. One definition based on the displacements relative to the ideal lattice positions was used to compare the Molecular Dynamics results with data from experiments combining ion implantations and channeled Rutherford Backscattering analyses. A second definition based on atomic coordination was used to compare the Molecular Dynamics results to those yielded by a simplified elastic model. The simulation results using the lattice-based definition of the amorphous fraction compare very well with the experimental results. This proves that the modeling in two steps chosen for the creation of the amorphous regions is reasonable. Moreover, the results show very clearly that SiC swelling does not scale linearly with the amorphous fraction introduced. Two swelling regimes are observed relatively to the size of the amorphous area. Comparison of the elastic model with the Molecular Dynamics results using the coordination-based definition of the amorphous fraction has also enabled us to shed light on the swelling mechanisms and has shown that amorphization-induced swelling exhibits an elastic behavior. Furthermore, scalings for the swelling as a function of the two amorphous fractions considered, which can be used by larger scale models, have been determined. Finally, our study shows that classical Molecular Dynamics calculations enable one to connect the results of the available experiments with the elastic calculations and to get further insight into the swelling mechanisms.

Solid phase epitaxy of Na-ion irradiated α-quartz: Cathodoluminescence, kinetics and surface morphology

Even at low fluences doping of quartz by ion implantation results in amorphization. Here we report on the measurement of cathodoluminescence and surface structures during solid phase epitaxy in Na-implanted α-quartz annealed in 18O2 atmosphere. Complete epitaxy was achieved under appropriate conditions of ion fluence, annealing temperature and time. The crystalline structure of the samples was studied by Rutherford backscattering channelling spectroscopy and the 18O–16O exchange between the matrix and 18O2 annealing gas by elastic recoil detection analysis. In the cathodoluminescence spectra taken at room temperature, five bands were identified and assigned to various defect centres. Two of the bands in the violet region at 3.25 and 3.65eV strongly vary in intensity at 843–1173K annealing temperature and appear to be intimately correlated with the presence of Na-ions in the implanted region of the matrix. Finally, atomic force microscopy enabled, for the first time, the observation of the correlation of surface structures and epitaxy.

A new iterative process for accurate analysis of displaced atoms from channeling Rutherford backscattering spectrometry

We have developed an iterative process to distinguish the yield contribution of the channeled He ions directly backscattered by displaced atoms and the yield contribution from the dechanneled He ions backscattered by lattice displaced atoms in channeling Rutherford backscattering spectrometry (RBS). The iterative process is able to accurately calculate the dechanneled fraction, the directly backscattered fraction and the dechanneling cross-section. It can also improve the accuracy of quantitative analysis of disorder profiles in monocrystalline solids by using channeling RBS. We demonstrate this technique by applying it to the measurement of the disorders in Si induced by 60keV 1H+ ion implantation to a fluence of 7×1016cm−2.

Low temperature air-annealing of Cu(InGa)Se 2 single crystals

CuInSe 2 and CuIn 0.95Ga 0.05Se 2 single crystals, grown by vertical Bridgman, were annealed in air at temperatures from 100 to 160 °C. Both CuInSe 2 and CuIn 0.95Ga 0.05Se 2 samples were studied using photoluminescence (PL). The CuInSe 2 samples were also studied using Rutherford Backscattering Channeling (RBS/C) and nuclear reaction analysis (NRA). Before annealing the samples showed low dechanneling parameters suggesting high quality lattice structure. The PL spectra of both CuInSe 2 and CuIn 0.95Ga 0.05Se 2 revealed bands associated with band-tail recombination mechanism. Annealing at 120 °C and higher temperatures considerably modified the RBS/C and PL spectra. NRA indicated a gradual increase in the oxygen content. PL analysis suggested that annealing increases both the mean-square amplitude of potential fluctuations and the level of compensation. Changes in the RBS/C spectra demonstrated that annealing at up to 160 °C does not result in the growth of In 2O 3 surface layer but modifies primarily the Se- and Cu-related RBS/C yield. These modifications are consistent with an increase in the concentration of defect complexes.

Charge-state dependence of energy loss of MeV dimers inGaAs(100)

Carbon and oxygen dimers with charge states $1+$ and $3+$ were implanted into $\mathrm{GaAs}$ along the [100] direction at an energy of $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{atom}$. The defect depth profiles are extracted from Rutherford backscattering spectrometry and channeling. The depth profile of carbon is extracted from secondary ion mass spectrometry measurements. The defect density produced by dimer ions is larger than monomer ions. The depth profile of carbon in dimer implanted $\mathrm{GaAs}$ is deeper than that of monomer implanted $\mathrm{GaAs}$ showing negative molecular effect. The defect depth profile of oxygen dimer implanted $\mathrm{GaAs}$ is deeper for $3+$ than that for $1+$ charge state. This indicates that energy loss of ${\mathrm{O}}_{2}^{3+}$ is smaller than that of ${\mathrm{O}}_{2}^{+}$. It is attributed to charge asymmetry and a higher degree of alignment of ${\mathrm{O}}_{2}^{3+}$ along the [100] axis of $\mathrm{GaAs}$.

Growth and properties of epitaxial rare-earth scandate thin films

Epitaxial rare-earth scandate thin films of 100–1500 nm in thickness have been prepared by pulsed laser deposition on SrTiO3(100) and MgO(100) substrates. Stoichiometry and crystallinity were investigated by Rutherford backscattering spectrometry/channelling (RBS/C), transmission electron microscopy, and X-ray diffraction. Electrical measurements on microstructured capacitors with a SrRuO3 bottom electrode and Au top contacts reveal dielectric constants of 20 to 27, leakage currents of 0.85 to 6 μA/cm2 at 250 kV/cm, and breakdown fields of 0.6 to 1.2 MV/cm. The optical bandgaps of the films range from 5.5 to 6 eV. The results substantiate the high potential of rare-earth scandates as alternative gate oxides.

NITROGEN LATTICE LOCATION IN MOVPE GROWN Ga1-xInxNyAs1-y FILMS USING ION BEAM CHANNELING

We have investigated the nitrogen lattice location in MOVPE grown Ga 1- x In x N y As 1- y with x = 0.07 and y = 0.025 by means of ion beam channeling technique. In this system, the lattice constant of the Ga 1- x In x N y As 1- y film is equal to GaAs lattice. Therefore, we can grow apparently no strain, high quality and very thick GaInNAs film on GaAs substrate. The quality of the films as well as the lattice location of In and N were characterized by channeling Rutherford backscattering spectrometry and nuclear reaction analysis using 3.95 MeV He 2+ beam. The fraction of substitutional nitrogen in the film was measured using the 14 N (α, p )17 O endothermic nuclear reaction. Our results indicate that more than 90% of In and N atoms are located the substitutional site, however, N atoms are slightly displaced by ~0.2 Å from the lattice site. We suggest that the GaInNAs film has a local strain or point defects around the N atoms.

Study of radiation damage in Mg+-implanted GaN

The GaN films grown on sapphire by metal-organic chemical vapor deposition (MOCVD) have excellent crystalline quality (χmin=2.00%). Combining Rutherford backscattering/channeling (RBS/C) and high-resolution X-ray diffraction (HXRD) measurements, we investigate the radiation damage in GaN films with various doses and angles of Mg+-implantation. The results of experiments reveal that the radiation damage rises with the increasing implantation dose. Under the dose of 1×1015atom/cm2, χmin is less than 4.78%, and when implantation dose exceeds the threshold of 1×1016atom/cm2, χmin will be up to 29.5%. Random implantation causes more serious damage than channeled implantation, and in a definite range the damage level rises with a larger implantation angle. At the implantation angles of 0°,4°,6°and 9°deviating from〈0001〉, χmin(%)is 6.28,8.46,10.06 and 10.85, respectively, at a dose of 4×1015atom/cm2. After annealing at 700℃ for 10min and then 1050℃ for 20s, the damage recovers to some extend. The crystalline quality of the sample with 1×1016atom/cm2 implanted was reduced to 19.08%. In addition, the annealing condition of 1000℃ for 30s is more efficient and the damage recovers better.

Ab initiostructures ofAsmVcomplexes and the simulation of Rutherford backscattering channeling spectra in heavily As-doped crystalline silicon

Geometrical models of neutral single vacancy-arsenic complexes are determined from first principles and used for atomistic simulation of Rutherford backscattering channeling (RBS-C) spectra in heavily As-doped crystalline silicon, both with and without compensating Si self-interstitials. The goal is to investigate whether the relaxation patterns of complexes containing different numbers (from 1 to 4) of As atoms can be used as a fingerprint in structural analysis by conventional RBS-C. Simulation of RBS-C spectra in million-atoms supercells containing a population of ${\mathrm{As}}_{m}\mathrm{V}$, show the off-lattice displacement of the Si atoms neighboring the vacancy, due to Jahn-Teller effect. On the other side, As displacement is found to be similar in all clusters investigated. The present results suggest that in the case of samples equilibrated at high temperature, the lack of any significant disorder of Si atoms is consistent with the hypothesis of electrically inactive As being in the form of either ${\mathrm{As}}_{3}\mathrm{V}$ or ${\mathrm{As}}_{4}\mathrm{V}$ complexes.

Self-assembling of nanocavities inTiO2dispersed with Au nanoclusters

There has been considerable research effort on tailoring the nonlinear optical properties of dielectric materials by dispersing nanometer-sized metallic clusters in them. It has been proposed that the optical response of this type of material is related to the quantum antidots (vacancy clusters), which is spatially located at the interface between the metal cluster and the dielectric matrix. In order to clarify the vacancy clustering behavior as well as its correlation with Au clustering, single crystal ${\mathrm{TiO}}_{2}$ has been implanted with Au ions at $975\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and subsequently annealed at $1275\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $10\phantom{\rule{0.3em}{0ex}}\mathrm{h}$. A characteristic self-assembling of nanocavities along the boundary between the region of Au clusters and the free surface has been observed in the present system. These cavities are faceted along ${\mathrm{TiO}}_{2}(110)$ and have a size of $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. High angle annular dark-field (HAADF) imaging in an aberration corrected scanning transmission electron microscope (STEM) revealed that vacancy clusters of $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in size also exist in the Au populated regions. Formation of cavities in Au-irradiated ${\mathrm{TiO}}_{2}$ strongly indicates that vacancy clustering processes prevail over Frenkel-pair recombination. Furthermore, the Au atoms substitution for Ti in ${\mathrm{TiO}}_{2}$ is also directly observed by STEM-HAADF imaging and by channeling Rutherford backscattering spectrometry.

Temperature dependent diffusion and epitaxial behavior of oxidized Au/Ni/p-GaN ohmic contact

The temperature dependent diffusion and epitaxial behavior of oxidized Au/Ni/p-GaN ohmic contact were studied with Rutherford backscattering spectroscopy/channeling (RBS/C) and synchrotron X-ray diffraction (XRD). It is found that the Au diffuses to the surface of p-GaN to form an epitaxial structure on p-GaN after annealing at 450 °C. At the same time, the O diffuses to the metal–semiconductor interface and forms NiO. Both of them are suggested to be responsible for the sharp decrease in the specific contact resistance ( ρ c) at 450 °C. At 500 °C, the epitaxial structure of Au develops further and the O also diffuses deeper into the interface. As a result, the ρ c reaches the lowest value at this temperature. However, when annealing temperature reaches 600 °C, part or all of the interfacial NiO is detached from the p-GaN and diffuses out, which cause the ρ c to increase greatly.

Thermal stability of ion-implanted ZnO

Zinc oxide single crystals implanted at room temperature with high-dose (1.4×1017cm−2) 300 keV As+ ions are annealed at 1000–1200 °C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO.

Interfaces in heterostructures of AlInGaN/GaN/ Al2O3

Rutherford backscattering/channeling (RBS/C) and X-ray diffraction (XRD) are used to comprehensively characterize a heterostructure of AlInGaN/GaN/Al2O3(0001). The AlInGaN quaternary layer was revealed to process a high crystalline quality with a minimum yield of 1.4% from RBS/C measurements. The channeling spectrum of (1 (2) under bar 13) exhibits higher dechanneling than that of (0001) at the interface of AlInGaN/GaN. XRD measurements prove a coherent growth of AlInGaN on the GaN template layer. Combining RBS/C and XRD measurements, we found that the interface of GaN/Al2O3 is a nucleation layer, composed of a large amount of disorders and cubic GaN slabs, while the interface of AlInGaN/GaN is free of extra disordering (i.e. compare with the GaN layer). The conclusion is further evidenced by transmission electron microscopy (TEM). (c) 2005 Elsevier Ltd. All rights reserved.

Irradiation fluence dependent microstructural evolution of porous InSb

Ion irradiation of InSb yields not only amorphization but also causes the material to become porous. This irradiation-induced porosity in InSb has been investigated using implantation of 1MeV 69Ga+ ions. Initially, voids form which then develop into a sponge-like structure. Further irradiation generates a network of rods ∼20nm in diameter. The precursors to porosity, i.e. small voids and dislocation loops, are apparent with transmission electron microscopy in the damaged region below the porous layer. Rutherford backscattering spectrometry and channeling indicates that damage to the crystalline lattice builds up more rapidly in implants performed at liquid nitrogen temperature than at room temperature.

Generation of amorphous surface layers in LiNbO3 by ion-beam irradiation: thresholding and boundary propagation

The refractive-index profiles induced by high-energy (5 MeV, 7.5 MeV) silicon irradiation in LiNbO3 have been systematically determined as a function of ion fluence in the range 1013–1015 cm-2. At variance with irradiations at lower energies, an optically isotropic (‘amorphous’) homogeneous surface layer is generated whose thickness increases with fluence. These results have been associated with an electronic excitation mechanism. They are discussed in relation to the well-documented phenomenon of latent (amorphous) track generation under ion irradiation, requiring a threshold value Se,th for the electronic stopping power Se. Our optical data have yielded a value of ≈5 keV/nm for such a threshold, within the range reported by independent single-track measurements. The propagation of the amorphous boundary into the crystal during irradiation indicates that the threshold value decreases on increasing the fluence. Complementary Rutherford backscattering–channeling and micro-Raman (on samples irradiated at 30 MeV) experiments have been performed to monitor the induced structural changes.

Cathodoluminescence and epitaxy after laser annealing of Cs+-irradiated α-quartz

In the course of a systematic investigation of dynamic, chemical, and laser-induced solid phase epitaxy of α-quartz after ion implantation, we have studied epitaxy and cathodoluminescence emission after 250 keV Cs-ion implantation and subsequent pulsed excimer laser treatment in air. Rutherford backscattering channelling analysis showed partial epitaxy for all the laser-irradiated samples; however, no full epitaxy was achieved. The optical properties of these samples were analyzed using cathodoluminescence spectroscopy, giving evidence of five emission bands at 2.42, 2.79, 3.25, 3.65, and 4.30 eV photon energy. Their intensity relation to the laser power and retained Cs-ion fraction are discussed and the present results will be compared with those obtained after chemical and dynamic epitaxy of quartz after alkali-ion, Ge, and Ba implantation.