Rutherford Backscattering Channeling Research Articles

Correlation of Mn lattice location, free hole concentration, and curie temperature in ferromagnetic GaMnAs

We provide experimental evidence that the electrical and magnetic characteristics of Ga 1-x Mn x As for a given x depend primarily on the distribution of Mn atoms over their different possible locations in the crystal lattice. Using combined channeling Rutherford backscattering and particle-induced X-ray emission, we show that optimal postgrowth annealing-which leads to an increase of the Curie temperature T C and is accompanied by an increase of free hole concentration and saturation magnetization-is caused by the reduction in the number of Mn atoms occupying interstitial positions. On the other hand, when Ga 1-x Mn x As is additionally doped with Be, we observe that-while the hole concentration remains nearly constant-there occurs a strong decrease of T C together with a dramatic increase in the concentration of Mn interstitials. These results indicate that there is a thermodynamic limit imposed on the maximum Curie temperature in Ga 1-x Mn x As.

RBS and ion channelling study of YBCO/STO and YBCO/LSMO/STO structures. Oxygen content estimated by X-ray diffraction

The structure and the elemental depth distributions of Y 1Ba 2Cu 3O 7− δ (YBCO) and La 0.7Sr 0.3MnO 3 (LSMO) were examined by θ−2 θ XRD, and by 1.7 MeV 4He + Rutherford Backscattering Spectrometry (RBS) in random and channelling geometry. The YBCO layers were magnetron sputtered, with the varying parameters oxygen pressure and annealing time. The layers have high crystalline quality and an almost sharp interface with the substrate as revealed by the analysis. It is shown that the oxygen content influences considerably not only the superconducting behaviour, but also the lattice parameters and the χ min parameter (the minimum yield which is the ratio of aligned to random Rutherford backscattering spectra). We have found by high-precision RBS simulation that, independent on the film quality, a disordered interface region of 20–30 nm is present in all structures. As a complementary study we have performed also AES depth profiling.

Effect of low dose high energy O3+ implantation on refractive index and linear electro-optic properties in X-cut LiNbO3: Planar optical waveguide formation and characterization

X-cut LiNbO3 crystals were implanted at room temperature by 5.0 MeV O3+ ions with doses ranging from 1.0×1014 to 6.0×1014 O/cm2. Secondary ion mass spectrometry profiles of atomic species migration as well as damage profiles by the Rutherford backscattering channeling technique and refractive index variation were investigated as a function of dose and subsequent annealing conditions. Two different kinds of damage produced by oxygen implantation were seen: near-surface damage correlated to electronic stopping, which causes an increase of the extraordinary refractive index, and end-of-ion range damage generated by collision cascades, which decreases the extraordinary refractive index values. The different nature of the two kinds of damage is also seen by the different temperature conditions needed for recovery. Low loss planar optical waveguides were obtained and characterized by the prism coupling technique.

Application of ion beam techniques in superconducting electronics

In superconducting electronics ion beams are used traditionally in deposition of thin films by magnetron sputtering and in patterning films by dry ion etching. By means of ion implantation one can fabricate also weak links (Josephson junction) from high- T c materials. If multiple ion implantation with different energy and doses is used, it is possible to improve ion implanted high critical temperature weak links either by creating a homogeneous profile or by forming a conducting channel inside the film. In this paper we present investigation of the properties of oxygen ion modified YBCO films intended to be used as barriers in HT c Josephson junctions by optical methods and Rutherford backscattering spectroscopy and channelling.

Irradiation-induced improvement of crystalline quality of epitaxial Cu/Si(100) films

We have demonstrated that ion-irradiation greatly improves the crystalline quality of epitaxial grown Cu films on Si(100) substrates. For the Cu/Si system, it is well known that thermal annealing is inapplicable to the improvement of the crystalline quality of the Cu films because inter-diffusion easily occurs at the Cu/Si interfaces at temperatures as low as 470 K. Accordingly, ion-irradiation is used to anneal the epitaxial Cu films. Irradiation with 0.5 MeV 28Si ions was carried out to doses ranging from 1×10 16 to 4×10 16 cm −2 at temperatures of 323 and 123 K. The quality of the Cu crystalline films (∼80 nm thick) was analyzed by Rutherford backscattering spectrometry/channeling (RBS/C) before and after irradiation. In the RBS/C spectra, the minimum yield at the Cu surface decreases from 90% to 42% after irradiation to 3×10 16 cm −2 at 323 K. On the other hand, the minimum yield at the Cu/Si interface decreases up to 2×10 16 cm −2, but increases above that dose due to the reaction between the Cu film and the Si substrate. It is found that irradiation at 123 K effectively prevents the interfacial reaction. The RBS/C analysis reveals that the improvement of the crystalline quality of the Cu film is brought about by the decrease in mosaic spread in the Cu film. Also, it is suggested that collision-induced atomic rearrangements reduce the mosaic spread in the Cu film.

Modification of new photoelectric material GaN by implantation of H +, He + and N + ion beam

The structure and crystal quality of GaN using Rutherford Backscattering Spectrometry and Channeling were studied. The samples were grown on sapphire by metal-organic vapor-phase epitaxy. The H +, He +, N + with different ion energies and doses were implanted into GaN. Post-implantation annealing were investigated. We observed 7–8 orders increasing of resistivity by Hall measurements after specific temperature annealing, and the optimized annealing temperature is approximately 200–400 °C for H +, He + and N + respectively. Even after 600–700 °C annealing, the resistivity is still very high. We think vacancies and radioactive damage by implantation are responsible for resistivity changes in GaN samples.

Effect of the location of Mn sites in ferromagneticGa1−xMnxAson its Curie temperature

We report a strong correlation between the location of Mn sites in ferromagnetic ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ measured by combined channeling Rutherford backscattering and by particle-induced x-ray emission experiments and its Curie temperature. The concentrations of free holes determined by electrochemical capacitance-voltage profiling and of uncompensated ${\mathrm{Mn}}^{2+}$ spins determined from superconducting quantum-interference device magnetization measurements are found to depend on the concentration of unstable defects involving highly mobile Mn interstitials. This leads to large variations in ${T}_{C}$ of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ when it is annealed at different temperatures in a narrow temperature range. The fact that annealing under various conditions has failed to produce Curie temperatures above \ensuremath{\sim}110 K is attributed to the existence of an upper limit on the free hole concentration in low-temperature-grown ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}.$

High-energy (MeV) Al and B ion implantations into 4H-SiC and fabrication of pin diodes

High-energy (MeV) implantation of Al+ or B+ into 4H-SiC epilayers has been investigated. A 3 μm deep pn junction was formed by multiple-step Al+ or B+ implantation with implantation energies up to 6.2 or 3.4 MeV, respectively. Rutherford backscattering channeling and cross-sectional transmission electron microscopy analyses have revealed residual damages in the implanted layers even after high-temperature annealing at 1600–1800 °C. Nevertheless, high electrical activation ratios over 90% have been achieved for both Al+- and B+-implanted layers by annealing at 1800 °C. Mesa pin diodes with a 15-μm-thick i layer formed by MeV implantation have exhibited high breakdown voltages of 2860–3080 V. The reverse characteristics of diodes have been substantially improved by increasing annealing temperature up to 1800 °C. The diode performance is discussed with the results of deep level analyses near the junctions.

Channeling energy loss of He 2+ in Si by transmission and back-scattering measurements: Experiments and computer modeling

Path-dependent electronic stopping of 3.35 MeV He 2+ ions in Si, is investigated by Rutherford back-scattering channeling in Si/SiO 2 wafers and transmission energy loss measurements in thin (1 1 0) membranes. A model which makes use of the 3-D Si electron density to calculate the stopping due to valence electrons, and the program convolution approximation for swift particles (CASP) to calculate the stopping due to core electrons, has been introduced into a Monte Carlo code for the simulation of channeling. The only adjustment allowed is the normalization to the empirical random stopping. An agreement of simulations and experiments within ±10–15% is obtained if both valence and core electron stopping components are scaled in the normalization procedure. To perform a significant comparison with the results obtained by a full atomic (CASP) model, we have also used a different normalization scheme, keeping the core component fixed and scaling only the valence electron contribution. In this case the results of the solid model, although slightly less accurate, become very similar to those obtained with the free-atom model.

Amorphization and annealing of LiTaO3 single crystal irradiated with Ar+ ions at 77 K

The defect structure of radiation damage due to irradiation of Ar+ ions and the regrowth of LiTaO3 single crystal has been studied using Rutherford backscattering-channeling, cross-sectional transmission electron microscopy, optical transmittance, and surface profilometer. The irradiation were carried out at 77 K with 217 keV Ar+ ions to various doses between 3×1013 and 6×1015 Ar+/cm2. Postannealing was performed in dry O2 ambient at temperatures from 648 to 823 K, which are below Curie temperature (878 K). The optical measurement showed that the as-irradiated samples are as transparent as the unirradiated sample, indicating that the radiation-induced point defects are highly mobile even at 77 K. However, the long-range migration of oxygen interstitials were suppressed at 77 K. Volumetric expansion occurred when irradiation doses exceeded 1.25×1014 Ar+/cm2. Collective lattice distortion was observed in the sample that had received a dose of 1.5×1014 Ar+/cm2. This study shows that both disorder overlapping and the disorder-induced strain energy play important roles in the amorphization process. The regrowth of the amorphized layers depends on the microstructure of the damage. The activation energy for the regrowth of the amorphized layer that received more irradiation (6×1015 Ar+/cm2) is 0.74 eV, lower than the activation energy of the amorphized layer (1.20 eV) that received less irradiation (6×1014 Ar+/cm2).

Remarkable lattice recovery and low sheet resistance of phosphorus-implanted 4H–SiC (112̄0)

High-dose ion implantation of phosphorus into 4H–SiC has been investigated. Phosphorus ion implantation with a 1×1016 cm−2 dose at 800 °C into 4H–SiC (0001) has resulted in a sheet resistance of 80 Ω/□ after annealing at 1700 °C. A similar sheet resistance of 110 Ω/□ was achieved even by room-temperature implantation when 4H–SiC (112̄0) was employed, owing to excellent recrystallization of this face revealed by Rutherford backscattering channeling spectroscopy. The sheet resistance could be further reduced down to 27 Ω/□ by 800 °C implantation into 4H–SiC (112̄0) followed by annealing at 1700 °C. 4H–SiC (112̄0) showed a very flat surface after annealing.

Planar MeV ion channeling on strained buried nanofilms

Planar MeV ion channeling experiments have been used to characterize a buried Si 1− x Ge x film with a thickness of 2.2 nm in a silicon host crystal. The tetragonal deformation in the film shows up as a translation of the {0 1 1} planes across the film, which was measured as a step in the yield of the planar channeled Rutherford backscattering spectra. The flux distribution between the planes acts as a probe for the position of the planes. The angular dependence of the step height has been measured for different incident ion energies and interpreted with Monte Carlo calculations. Simulations only resemble the measured spectra when the Hartree–Fock potential is used for the ion–atom interaction. The translation of the planes can be measured with an accuracy of approximately 10%, which is comparable to results obtained with axial channeling experiments.

Clustering in Pb thin films on Si(1 1 1) and Pb-induced Si surface ordering

Pb thin films (10 nm) were deposited from a Knudsen cell on sputter-cleaned Si(1 1 1) substrates under ultrahigh vacuum conditions. Films were deposited at room temperature and subsequently annealed at 300 °C for 30 min. Rutherford backscattering spectrometry and channeling (RBS/C) measurements did not show any channeling in the as-deposited as well as annealed Pb layer. For the annealed sample the spectral broadening in RBS/C spectra occurred due to clustering of Pb, with a simultaneous reduction in the minimum yield from the Si substrate. Prior to Pb deposition the sputter-cleaned Si substrate was annealed at 500 °C, which was insufficient to remove all the damages introduced by Ar + sputtering. Thus the reduction of minimum yield in the substrate for the annealed Pb/Si(1 1 1) system compared to unannealed Pb/Si(1 1 1) may be interpreted as Pb-induced ordering of the Si surface. From the analysis of the step structure observed near the Si edge of the RBS/C spectrum for the annealed sample, it was found that Pb islands (average height ∼35 nm) have been formed on a uniform Pb layer of ∼1 nm thickness. The island formation has been confirmed by atomic force microscopy measurements.

Structural, optical and electrical properties of the novel semiconductor alloy ZnOxTe(1-x)

ABSTRACTEpitaxial films of undoped ZnOxTe(1-x) have been prepared on double-side polished c-axis oriented sapphire substrates with pulsed laser deposition. The method of epitaxial growth is expected to have the same domain matching epitaxial relationship with sapphire as does pure ZnO, where six lattice planes of ZnOxTe(1-x) match with seven lattice planes of sapphire [1,2]. High quality, single crystal, epitaxial alloys with around 4% Te have been grown that demonstrate excellent optical properties and a pronounced, sharp excitonic peak, in optical transmission. The incorporation of Te makes the compound more covalent, and less ionic than pure ZnO. Transmission electron microscopy (TEM) demonstrates single-crystal growth with a sharp interface. The low-resolution X-ray diffraction (XRD) pattern of ZnOxTe(1-x) films is almost indistinguishable from those of pure ZnO, except a usually diminished intensity of the (0004) peak. The incorporation of Te in ZnO was verified by a shift in excitonic peak position in absorption, and through a shift in cathodoluminescence (CL) peak. X-ray photoelectron spectroscopy (XPS) data verifies incorporation of telluride chemical state of tellurium atoms. Rutherford backscattering/channeling (RBS/C) confirmed crystal quality for the pure ZnO films. Hot-point probe measurements indicate as-grown, undoped films to be somewhat higher in resistivity than pure ZnO with inconclusive carrier type, as compared to the naturally n-type ZnO. This may be a consequence of the more covalent bonding between Zn and Te and suggests a possible strategy for p-type doping.

Electrical Characteristics of Sol-Gel Derived (100) Oriented Ba 0.5 Sr 0.5 TiO 3 Thin Films on LaAlO 3 (100) Substrates

The nature of in-plane epitaxy and texture quality of highly oriented (100) Ba 0.5 Sr 0.5 TiO 3 [BST (50/50)] thin films on (100) LaAlO 3 (LAO) substrates were analyzed using X-ray pole figure analysis and RBS channeling measurements. The temperature dependent (100 to 325 K) electrical properties of the BST (50/50) films were characterized in terms of their low frequency (<1 MHz) dielectric behavior, ferroelectric properties and leakage current characteristics. Mn doping up to 3 at % was found to increase the phase shift from 260° (undoped film) to 340° (at 400 V). However, the insertion loss was also increased from 6.34 dB to 9.52 dB with Mn doping and as a result there was no appreciable improvement in the s factor (∼35 to 41°/dB). The observed microwave properties are correlated in terms of the degree of texturing and surface morphology of these films.

Resonant Rutherford backscattering spectrometry and channeling studies on the effect of annealing of La 0.67Ca 0.33MnO 3 epilayers grown on SrTiO 3( [formula omitted]) substrates using a facing-target sputtering technique

La 0.67Ca 0.33MnO 3 films are known to release oxygen upon vacuum annealing due to lattice expansion caused by change of valence state of Mn from Mn 4+ to Mn 3+. RBS measurements using O( α, α) resonance reaction at 3.043 MeV show that oxygen concentration decreases from 60% to 57% in 450 °C-vacuum annealed samples. There is also oxygen loss from the SrTiO 3 substrate upto a certain depth. The measure of crystalline quality χ min degrades from 5.9% to 10%. A 45° in-plane orientation is observed which is due to the dominant presence of [1 1 0] 0 texture in the epilayer. The measured channeling half width ψ 1/2 decreases upon vacuum annealing. In the samples annealed in oxygen at high pressure at 700 °C, there is no measurable change in oxygen concentration and χ min improved to 4.4%. ψ 1/2 increases upon high pressure oxygen annealing. Our measurements directly show that there is lattice disorder upon vacuum annealing and ordering upon high pressure oxygen annealing and it is the largest for the oxygen lattice sites.

Lattice deformation in InAs/GaAs superlattices characterized by MeV ion channeling

Axial and planar MeV ion-channeling experiments are performed on a InAs/GaAs superlattice with ten coherent buried InAs nanofilms in GaAs. We have measured a step in the channeled Rutherford backscattering spectra, which depends on the incidence angle of the ions. With Monte Carlo simulations, the average tetragonal distortion in the nanofilms can be determined from the axial channeling measurements, although the separate contributions of each individual nanofilm cannot be resolved in the measured spectra. Planar channeling measurements show a higher step, but a detailed resemblance between measurements and simulations cannot be achieved.

Study of ion implanted Al0.25Ga0.75As/GaAs by Raman spectroscopy

This paper reported the effect of the weak damage in the Al 0.25 Ga 0.75 As/GaAs epitaxial layer induced by 0.8 MeV Si ions implantation with ion dose from 1×10 14 to 5×10 15 cm -2 . The Raman spectra measured on these samples showed that there were two kinds of phonon modes existing in the epitaxial Al 0.25 Ga 0.75 As films. The strains induced in the implanted layer and the corresponding lattice parameters were also evaluated as a function of the implanted dose. In addition, the Rutherford backscattering spectrometry/channeling (RBS/C) was also measured on these samples. These two measurement techniques all confirmed that the implantation only induced weak damage in the material.

Investigation of H + and B +/H + implantation in LiTaO 3 single-crystals

LiTaO 3 single-crystals have been implanted by hydrogen or boron mixed with hydrogen ions. The behavior of ion implantation and annealing has been investigated because they are the essential problems to be investigated for checking the possibility to realize LiTaO 3 single-crystal layer transfer on other substrates. Optical microscope image shows that LiTaO 3 implanted with 5×10 16 ions/cm 2 H + will generate bubbles at the temperature of 250 °C with air ambient. Atomic force microscopy (AFM) image shows that the bubbles would make the surface of LiTaO 3 split at 600 °C, but the samples that have been implanted with both B + and H + did not generate any bubbles, even when annealed at temperatures as high as 800 °C for 20 min in air ambient. The damage behavior and/or internal stress because of ion implantation and recovery of damage after annealing were also investigated by X-ray rocking curves and Rutherford backscattering spectroscopy and channeling (RBS/C).

Channeling on boron clusters in silicon

Low energy ion implantation at high doses of boron (&amp;gt;1015 cm−2) in Si is necessary for the fabrication of ultrashallow junctions but can result in the undesirable presence of boron clusters. Values for the dimensions of the lattice distortions in the implanted Si are obtained by comparing the enhanced dechanneling and the direct scattering peak in the region with clusters in a channeled Rutherford backscattering spectrometry spectrum to those from Monte Carlo calculations on a curved crystal structure. Values of about 0.17 and 65 nm are found for the maximum deformation and the length of the distortions in the crystal, respectively, which implies that the lattice distortions extend significantly outside the layer in which the B clusters are supposed to be present.