Rutherford Backscattering Ion Channeling Research Articles

On the manifestation of phosphorus-vacancy complexes in epitaxial Si:P films

In situ doped epitaxial Si:P films with P concentrations >1 × 1021 at./cm3 are suitable for source-drain stressors of n-FinFETs. These films combine the advantages of high conductivity derived from the high P doping with the creation of tensile strain in the Si channel. It has been suggested that the tensile strain developed in the Si:P films is due to the presence of local Si3P4 clusters, which however do not contribute to the electrical conductivity. During laser annealing, the Si3P4 clusters are expected to disperse resulting in an increased conductivity while the strain reduces slightly. However, the existence of Si3P4 is not proven. Based on first-principles simulations, we demonstrate that the formation of vacancy centered Si3P4 clusters, in the form of four P atoms bonded to a Si vacancy, is thermodynamically favorable at such high P concentrations. We suggest that during post epi-growth annealing, a fraction of the P atoms from these clusters are activated, while the remaining part goes into interstitial sites, thereby reducing strain. We corroborate our conjecture experimentally using positron annihilation spectroscopy, electron spin resonance, and Rutherford backscattering ion channeling studies.

Role of the substrate on the magnetic anisotropy of magnetite thin films grown by ion-assisted deposition

Magnetite (Fe3O4) thin films were deposited on MgO (001), SrTiO3 (001), LaAlO3 (001) single crystal substrates as well on as silicon and amorphous glass in order to study the effect of the substrate on their magnetic properties, mainly the magnetic anisotropy. We have performed a structural, morphological and compositional characterization by X-ray diffraction, atomic force microscopy and Rutherford backscattering ion channeling in oxygen resonance mode. The magnetic anisotropy has been investigated by vectorial magneto-optical Kerr effect. The results indicate that the magnetic anisotropy is especially influenced by the substrate-induced microstructure. In-plane isotropy and uniaxial anisotropy behavior have been observed on silicon and glass substrates, respectively. The transition between both behaviors depends on grain size. For LaAlO3 substrates, in which the lattice mismatch between the Fe3O4 films and the substrate is significant, a weak in-plane fourfold magnetic anisotropy is induced. However when magnetite is deposited on MgO (001) and SrTiO3 (001) substrates, a well-defined fourfold in-plane magnetic anisotropy is observed with easy axes along [100] and [010] directions. The magnetic properties on these two latter substrates are similar in terms of magnetic anisotropy and coercive fields.

Optical properties of pseudomorphic Ge1−xSnx (x = 0 to 0.11) alloys on Ge(001)

The characterization of the optical properties of pseudomorphic Ge1−xSnx/Ge/Si (x = 0 to 0.11) alloys from the IR to UV is presented. The Ge1−xSnx alloys were epitaxially grown on relaxed Ge grown on Si. Rutherford backscattering (RBS) and RBS ion channeling methods were used to confirm the Sn composition and substitutional nature of the Sn into the Ge lattice. The pseudomorphic nature of the Ge1−xSnx on Ge is confirmed using high resolution x-ray diffraction (HRXRD) and transmission electron microscopy. Although HRXRD reciprocal space maps indicated that the Ge1−xSnx was pseudomorphic to Ge, the shape of the Bragg peaks indicated that the sample surface was rough. The rough surface morphology is confirmed using atomic force microscopy. The complex dielectric function is reported in the IR, visible, and UV spectrum in the wavelength range of 0.2–5.06 eV. The E1, E1 + Δ1, E2, and E0 critical points are extracted using second and third derivative line shape fitting and are compared with the elastic theory calculations of strained Ge1−xSnx (x = 0 to 0.11) alloys and fully relaxed Ge1−xSnx (x = 0 to 0.11) alloys. The E0 critical point energies are observed to have slightly larger values than those calculated for completely relaxed Ge1−xSnx alloys due to the presence of compressive strain.

Investigation of Si/SiGe/Si heterostructure implanted by H ion and annealed in vacuum and dry O2 ambient

The 20-nm-thick Si cap layer/74-nm-thick Si0.72Ge0.28 epilayer/Si heterostructures implanted by 25keV H+ ion to a dose of 1×1016cm−2 were annealed in ultra-high vacuum ambient and dry O2 ambient at the temperature of 800°C for 30min, respectively. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristics of the Si0.72Ge0.28 layer. Investigations by RBS/C demonstrated that the crystal quality of the Si/Si0.72Ge0.28/Si heterostructure sample implanted by 25keV H+ in conjunction with subsequent annealing in dry O2 ambient is superior to that of identical sample annealing in ultra-high vacuum ambient. The less strain relaxation of SiGe layer of the Si/Si0.72Ge0.28/Si heterostructures implanted by H ion and annealed in dry O2 ambient at the temperature of 800°C for 30min could be doublechecked by Raman spectra as well as HRXRD, which was compared with that in an identical sample annealed in ultra-high vacuum ambient for identical thermal budget. In addition, the SiGe layer of the H-implanted Si/SiGe/Si heterostructural sample annealed in dry O2 ambient accompanied by better crystal quality and less strain relaxation made its surface morphology superior to that of the sample annealed in ultra-high vacuum ambient at the temperature of 800°C for 30min, which was also verified by AFM images.

Characterization of strained silicon on relaxed SiGe layer made by H ion implantation and annealing in ultra-high vacuum ambient

Twenty-nanometer-thick Si cap layer/74-nm-thick Si 0.72Ge 0.28 epilayer/Si heterostructural sample was implanted by 25 keV H + ion to a dose of 1 × 10 16 cm −2 and subsequently annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristic of Si/SiGe/Si heterostructure. Investigations by RBS/C demonstrate that the Si 0.72Ge 0.28 layer show good crystal quality (21.1% of channel minimum yield). The relaxation degree of partially relaxed Si 0.72Ge 0.28 layer was around 74%, which was obtained by HRXRD. The computation process of the relaxation degree of strain in SiGe layer according to HRXRD rocking curve was also thoroughly introduced. Raman analysis revealed that stress, σ and strain, ε in the thin strained-Si layer were around 1.2 Gpa and 0.52%, respectively. In addition, the small surface roughness in the formed strained-Si/relaxed Si 0.72Ge 0.28 layer/Si heterostructural sample was observed via AFM image.

Search for ferromagnetism in conductive Nb:SrTiO3 with magnetic transition element (Cr, Co, Fe, Mn) dopants

Thin films of (0.5%, 1%) Nb:SrTiO3 dilutely doped with (2at.%) magnetic transition elements (Cr, Co, Fe, Mn) are examined for ferromagnetism. X-ray diffraction, Rutherford backscattering ion channeling, scanning transmission electron microscopy Z-contrast imaging, and electron energy loss spectroscopy techniques establish high crystalline quality of the films with no impurity phase(s) and highly uniform dopant distribution. Although the film conductivity improves dramatically by Nb doping, no ferromagnetism is found in any of our samples over the temperature range of 365 down to 5K. This is contrasted to the case of ferromagnetism reported in cobalt doped (La,Sr)TiO3.

Structure and optical properties of sapphire implanted with boron at room temperature and 1000 °C

Many previous studies of ion-implanted sapphire have used gas-forming light ions or heavier metallic cations. In this study, boron (1017cm−2, 150keV) was implanted in c-axis crystals at room temperature, 500 and 1000°C as part of a continuing study of cascade density and “chemical” effects on the structure of sapphire. Rutherford backscattering-ion channeling (RBS-C) of the RT samples indicated little residual disorder in the Al-sublattice to a depth of 50–75nm but almost random scattering at the depth of peak damage energy deposition. The transmission electron micrographs contain “black-spot” damage features. The residual disorder is much less at all depths for samples implanted at 1000°C. The TEM photographs show a coarse “black-spot damage” microstructure. The optical absorption at 205nm is much greater than for samples implanted with C, N, or Fe under similar conditions.

Growth of highly oriented HfO2 thin films of monoclinic phase on yttrium-stabilized ZrO2 and Si substrates by pulsed-laser deposition

We report on the growth of highly oriented HfO2 thin films of monoclinic phase stabilized by 5% Co doping on (001) yttrium-stabilized zirconia (YSZ) using pulsed-laser deposition at 700°C at an oxygen partial pressure of 10−4Torr. On the other hand, pure HfO2 of such quality did not grow on YSZ in wide range of growth parameters. Rutherford backscattering-ion channeling in this film showed a 24% minimum yield (χmin) indicating highly oriented film growth, while hardly any ion channeling was observed in the undoped sample. High-resolution transmission electron microscopy revealed a sharp interface, and no signature of Co clusters. Electron energy loss spectroscopy showed that Co is in the 2+ state. Attempts were also made to grow films on a (001) Si substrate, and the results showed a very low ion channeling yield (∼8%).

Synthesis of ternary SiGeSn semiconductors on Si(100) via SnxGe1−x buffer layers

Single-phase Si1−x−yGexSny alloys with random diamond cubic structures are created on Si(100) via ultrahigh vacuum chemical vapor deposition reactions of SnD4 with SiH3GeH3 at 350 °C. Commensurate heteroepitaxy is facilitated by Ge1−xSnx buffer layers, which act as templates that can conform structurally and absorb the differential strain imposed by the more rigid Si and Si–Ge–Sn materials. The crystal structure, elemental distribution and morphological properties of the Si1−x−yGexSny/Ge1−xSnx heterostructures are characterized by high-resolution electron microscopy, including electron energy loss nanospectroscopy, x-ray diffraction (rocking curves) and atomic force microscopy. These techniques demonstrate growth of perfectly epitaxial, uniform and highly aligned layers with atomically smooth surfaces and monocrystalline structures that have lattice constants close to that of Ge. Rutherford backscattering ion channeling shows that the constituent elements occupy random substitutional sites in the same average diamond cubic lattice and the Raman shifts are consistent with the lattice expansion produced by the Sn incorporation into SiGe tetrahedral sites.

Compositionally-tuned epitaxial cubic MgxZn1−xO on Si(100) for deep ultraviolet photodetectors

We report on the epitaxial growth of wide-band-gap cubic-phase MgxZn1−xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and MgxZn1−xO have been overcome by using a thin SrTiO3 buffer layer. The heteroepitaxy of cubic-phase MgxZn1−xO on Si was established with epitaxial relationship of MgxZn1−xO(100)//SrTiO3(100)//Si(100) and MgxZn1−xO[100]//SrTiO3[100]//Si[110]. The minimum yield of the Rutherford backscattering ion channeling in MgxZn1−xO layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg0.68Zn0.32O/SrTiO3/Si show peak photoresponse at 225 nm, which is in the deep UV region.

The structure of sapphire implanted with nitrogen at room temperature and 1000 °C

The structure of N-implanted sapphire (single crystal α-Al 2O 3) has been studied using Rutherford backscattering-ion channeling spectroscopy (RBS-C), transmission electron microscopy (TEM) and optical absorption. Specimens having the c-axis normal to the optically polished surface were implanted with 3×10 16 N/cm 2 (150 keV) at room temperature and 1000 °C. Little residual disorder was observed in the RBS-C spectra for the RT samples. A band of bubbles or voids (diameters 1–10 nm) extending from about 75 to 300 nm below the surface was observed in cross-sectioned TEM specimens. The disorder was greater in the 1000 °C sample and the TEM examination indicated the presence of extended defects lying parallel to the c-planes.

Growth and hydrogenation of epitaxial yttrium switchable mirrors on CaF 2

Rutherford backscattering (RBS) ion channeling measurements and X-ray diffraction experiments are performed to study the epitaxial nature of as-deposited yttrium on CaF 2〈111〉 substrates and the effect of hydrogenation on the crystalline quality. The RBS and X-ray results clearly demonstrate the unique epitaxial relation between as-deposited films and the substrate, which is preserved upon loading with hydrogen. X-Ray diffraction reveals: (i) a remarkably large lattice expansion in the direction normal to the substrate, which decreases with increasing film thickness; and (ii) an in-plane compression of the lattice. This peculiar result is related to the difference in thermal expansion coefficients of film and substrate. RBS ion channeling measurements reveal a thickness dependence of the mismatch-induced stresses. As expected, the stresses relax with increasing distance from the film/substrate interface, but surprisingly, even with films as thick as 400 nm considerable dechanneling is still observed at the film surface. Film quality, i.e. the film/substrate mismatch as well as the induced stresses and their relaxation, are discussed in relation to atomic force microscopy (AFM) results on these epitaxial films.

Incorporation site of Tbin GaN studied by Rutherford-backscattering ion channellingmeasurements and x-ray absorption fine-structure analysis

We report single-crystalline growth of Tb-doped GaN grown by gassource molecular beam epitaxy using NH3 as a nitrogensource, and the incorporation site of Tb in GaN. It was found thatmost of the Tb atoms are substitutionally incorporated into the Galattice site by Rutherford-backscattering ion channelling andextended x-ray absorption fine-structure analysis. Photoluminescence spectra, which show sharp peaks originatingfrom 4f intra-atomic transitions of Tb3+ ions, with near-band-edge emission of GaN, were observed from the film whose Tbcontent was roughly estimated to be 2%, and theirproperties are discussed.

Quenching mechanism of luminescence in Sm-doped ZnS

The quenching mechanism of luminescence by heavy Sm doping in ZnS was investigated by the Rutherford backscattering ion channeling (RBS/C) method. Red luminescence around 650 nm due to the 4f intra transition of Sm 3+ ion was observed in the Sm-doped ZnS, and the emission intensity becomes maximum at an Sm concentration of about 2×10 19 cm −3. The RBS/C measurements showed a much shallower dip in the angular profile of Sm yields and a shallower and broader Zn-dip in the heavily Sm-doped ZnS than those in the moderately Sm-doped sample. These results indicate that the quenching of the luminescence by heavy doping of Sm is caused by the deterioration of the structural quality of ZnS and the large displacement of Sm atoms from the lattice sites.

Compensation centers in ZnSeTe

Extended x-ray absorption fine structure (EXAFS), Rutherford-backscattering ion channeling, and particle induced x-ray emission channeling (PIXE/C) measurements have been performed in order to investigate compensation centers in Cl doped ZnSeTe. The EXAFS results from Cl doped ZnSeTe suggest that almost all Cl atoms are incorporated into substitutional Se lattice sites, which seems to indicate that Cl atoms themselves are not responsible for the compensation centers. The PIXE/C angular profiles were measured across the 〈100〉, 〈110〉, and 〈111〉 axes for undoped ZnSeTe. Comparing the angular profiles for Zn Kα, Se Kα, and Te Lα x-ray yields, it was found that some portion of the Te atoms (∼1020 cm−3) are located at tetrahedral interstitial sites. From these results, the difficulty of realizing n-type ZnSeTe is considered to be due to the existence of the interstitial Te atoms which act as acceptors.

Effect of crystal orientation on damage accumulation and post-implantation annealing for iron implantation into sapphire

This study confirms that the rate of damage accumulation is higher for sapphire crystals having the c-axis approximately parallel to the ion beam than for the a-axis orientation. Iron was implanted at room temperature to fluences of 1 × 10 16, 4 × 10 16 and 1 × 10 17 ions/cm 2 with an energy of 160 keV. Damage recovery was studied after annealing for 1 h in oxidizing and reducing atmospheres. The lattice disorder at the peak damage position was determined from Rutherford backscattering-ion channeling measurements. Recovery for the a-axis orientation was faster in the reducing atmosphere than in the oxidizing atmosphere. For the same implanted fluence, recovery in the a-axis crystals was faster than c-axis ones in the reducing atmosphere but slower in the oxidizing atmosphere.

Nanometer-size dispersions of iron in sapphire prepared by ion implantation and annealing

Abstract Some of the metal ions implanted into sapphire (single crystal α-Al2O3) are often present as metallic colloids or dispersions. Nano-composites consisting of iron particles in sapphire were prepared by implantation of 160 keV 56Fe at room temperature. The colloids were coarsened by annealing in the temperature range of 973–1673 K in a reducing atmosphere. Rutherford backscattering-ion channeling (RBS-C) and transmission electron microscopy (TEM) were used to determine the lattice damage as well as the nature, size and distribution of the iron. A range of particle sizes and shapes can be obtained by choice of implantation and/or annealing parameters.

Morphology of the implantation-induced disorder in GaAs studied by Raman spectroscopyand ion channeling

Disorder was introduced into GaAs by implantation of $^{30}\mathrm{Si}^{+}$ions, using a very wide range of ion doses, dose rates, and implant temperatures, and studied by Raman scattering (RS) and Rutherford backscattering ion channeling (RBS). RS spectra were deconvoluted consistently and systematically into up to four components, one of them being an apparent background signal interpreted here as a boson peak. Arguments are given that this signal represents the second amorphous phase different from a continuous random network. An intercascade distance model (ICD) was postulated, which estimates the average distance, ${\mathrm{L}}_{\mathrm{ICD}}$, between implantation-induced cascades as a function of ion dose. An analogous parameter, ${\mathrm{L}}_{\mathrm{RBS}}$, was calculated from the RBS damage fraction ${\mathrm{f}}_{\mathrm{RBS}}$. From RS data the correlation length ${\mathrm{L}}_{\mathrm{RS}}$, representing the size of crystalline regions with preserved translational symmetry, was determined by fitting the LO signal within the spatial correlation model. All three L's agree nicely, proving the equivalency of the correlation length and intercascade distance. This enabled a straightforward comparison of relevant signals and a direct correlation between RS and RBS. While measure of damage in RBS (${\mathrm{f}}_{\mathrm{RBS}}$) reflects the disordered volume fraction of the implanted layer, RS measures simultaneously the lowering of the translational symmetry (an effect that prevails at lower doses) and the fraction of disordered volume (prevailing at higher doses). A considerable difference in sensitivity between RS and RBS to particular defects enabled the differentiation of six different types of implantation-introduced disorder.

Ion beam mixing of chromium or zirconium films with sapphire

Ion beam mixing of thin metallic films deposited on sapphire substrates was studied for Cr or Zr films deposited on singlecrystal α-Al 2O 3 substrates. Evidence for the influence of equilibrium thermodynamic factors was sought by comparing the effects of bombarding with O ions (300 and 1073 K) with those of bombarding with Ne ions (300 K). Thermodynamic calculations indicate that mixing might occur for Zr/sapphire at 1073 K but not at 300 K. On this basis, Cr/sapphire should not mix at either temperature. The implantation energy placed the peak O concentration at the metal-sapphire interface in an attempt to maintain an equilibrium ratio of cations to anions to promote a radiation-induced chemical reaction across the interface. No evidence for long-range mixing was found from Rutherford backscattering-ion channeling measurements. Other experiments employed a heavier ion (Kr) as the mixing ion (300 K) in order to increase the mixing efficiency. Rutherford backscattering-ion channeling and X-ray photoelectron spectroscopy (XPS) were used to determine the extent and nature of any interface modification. The XPS results indicated that only metallic Cr was present near the interface in the as-deposited specimens and in those irradiated with Kr at 300 K. Zirconium exhibited only the metallic state (Zr 0) in the as-deposited film but was present as both Zr 0 and Zr 4+ after irradiation. Some metallic Al (Al 0) was detected near the Zr-sapphire interface after irradiation, suggesting that a local chemical reaction between Zr and the sapphire may have occurred during bombardment. No long-range material transport was detected for any experimental condition examined; the width of the “mixed” region in each case was below the limits of detection for RBS or consistent with that expected for ballistic effects.

Preparation of nanometer-size dispersions of iron in sapphire by ion implantation and annealing

Some of the metal ions implanted into sapphire (α-Al 2O 3) are often present as metallic colloids or dispersions. Nano-composites of iron colloids in sapphire were prepared by implantation of 160 keV Fe 56 at room temperature. The colloids were coarsened by annealing in the temperature range of 973 to 1673 K in a reducing atmosphere. Rutherford backscattering-ion channeling (RBS) and transmission electron microscopy (TEM) were used to determine the lattice damage as well as the nature, size and distribution of the iron. Second phase particles having diameters of 1–3 nm, and accounting for 45% of the implanted iron at a fluence of 1 × 10 17 Fe/cm 2 were identified by electron diffraction as having the α-Fe (body-centered cubic) structure. Annealing samples implanted at lower fluences produced metallic iron particles (3–20 nm diam.) with attached voids. The matrix was amorphous at 2 × 10 17 Fe/cm 2 and contained “strings” of crystalline iron particles (5–10 nm). Annealing in the reducing atmosphere produced iron platelets several hundreds nanometers long by 25–35 nm thick. It was observed that a range of particle sizes and shapes can be obtained by choice of implantation and/or annealing parameters.