Reciprocal Lattice Mapping Research Articles

Application of high-resolution x-ray diffraction for detecting defects in SiGe(C)materials

The application of high-resolution x-ray diffraction for detecting and distinguishing defectsin SiGe(C) layers is presented. A depth profile of the defects in SiGe/Si multilayers hasbeen performed by using high-resolution reciprocal lattice mapping at different asymmetricreflections. Transmission electron microscopy was also applied in order to observe defects inthe layers and these results were linked with the x-ray analysis. The substitutional C or Bconcentration in SiGe was measured by the shift of layer peak compared to the intrinsiclayers. The thermal stability of the SiGe layers was investigated in order to rank theepitaxial quality of the SiGe below the detection limit of x-ray technique. It has also beendemonstrated that x-ray analysis can be used for in-line process monitoring oflayers grown in small device openings on patterned substrates. These types ofanalysis have also been used routinely for the evaluation of processed samples.

Ion beam nitriding of single and polycrystalline austenitic stainless steel

Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 °C with 1.2 keV nitrogen ions using a high current density of 0.5mAcm−2. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the ⟨001⟩ being more preferential for nitrogen diffusion than ⟨011⟩. In both type of samples, XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

Damage in yttria-stabilized zirconia by Xe irradiation measured by X-ray diffraction

The evolution of microstructure in yttria-stabilized zirconia under irradiation is examined. YSZ was irradiated with Xe ions at 320 and 450keV. Transmission electron microscopy confirms the resulting dislocation network with no amorphization as previously reported in literature. Hi-resolution X-ray diffraction was used to further study the ion damage characteristics. θ–2θ scans measure an increasing out of plane lattice constant with dose. Reciprocal lattice maps indicate a strained surface layer, lattice matched to the unirradiated material.

Organometallic vapor phase epitaxy of GaAs1−xNx alloy layers on GaAs(001): Nitrogen incorporation and lattice parameter variation

Epitaxial GaAs1−xNx alloy layers, nominally 200-nm-thick, with x up to 0.0375 were grown on GaAs(001) at temperatures Ts varying from 500 to 650 °C to investigate nitrogen incorporation and lattice parameter variations during organometallic vapor phase epitaxy from trimethylgallium, tertiarybutylarsine, and 1,1-dimethylhydrazine. Quantitative secondary ion mass spectrometry measurements (SIMS) indicate that N incorporation decreases systematically with increasing Ts to become almost negligible at 650 °C. All films are coherent with the substrate as judged by high-resolution x-ray reciprocal lattice mapping although atomic force microscopy and cross-sectional transmission electron microscopy reveal the presence of cracks in films with x>0.02. High-resolution x-ray diffraction measurements combined with SIMS analyses indicate that the lattice constant decreases linearly with increasing x following closely the predictions of Vegard’s rule for x<0.03. At higher concentrations, the lattice constant decreases more rapidly as a significant fraction of N atoms becomes incorporated in nonsubstitutional sites as demonstrated by nuclear reaction analysis.

Misfit strain anisotropy in partially relaxed lattice-mismatched InGaAs/GaAsheterostructures

Partially relaxed InGaAs/GaAs heterostructures with a small lattice mismatch have beenstudied by means of atomic force microscopy and high-resolution x-ray diffractometry.Additionally, electron-beam induced current in a scanning electron microscopeand transmission electron microscopy have been employed to investigate misfitdislocations formed at the (001) heterostructure interface. The measurementsrevealed a direct correlation between the surface cross-hatched morphology and thearrangement of interfacial misfit dislocations. The reciprocal lattice mapping and therocking curve techniques employed for the samples aligned with either the or the [110] crystallographic direction perpendicular to the diffractionplane revealed anisotropic misfit strain relaxation of the InGaAs layers.This anisotropy results from an asymmetry in the formation of theα and β types of misfit dislocations oriented along the and [110] directions, respectively, which differ in their core structures. The misfit strainanisotropy causes a distortion of the unit cell of the layer and lowers its symmetry toorthorhombic.

Mechanisms of diffusion-enhanced thermal stability of Si/Si 1− xGe x/Si heterostructures grown by chemical vapor deposition

The thermal stability of doped Si/Si 0.8Ge 0.2/Si (n–p–n or p–n–p) structures grown by reduced pressure chemical vapor deposition has been studied in correlation with the dopant in- and out-diffusion, using high-resolution X-ray reciprocal lattice mapping and secondary ion mass spectrometry as the main characterization tools. Initially, by doping the strained Si 0.8Ge 0.2 layer with reasonable amounts of boron, phosphorus, or arsenic, the thermal stability of the structures is shown to be dramatically increased compared to intrinsic layers. Secondly, the results show that when the dopants are present only in the Si buffer and cap layers, intrinsic Si spacer layers are required to obtain a significant enhancement in the thermal stability. These spacers reduce the interfacial dopant concentration and act as barriers for direct injection of precipitates into the SiGe layers. Finally, p–n–p and n–p–n structures were studied, showing a very good thermal stability, due to enhanced out-diffusion of dopants from the SiGe layer upon in-diffusion from the adjacent layers. By employing i-Si spacers, the boron out-diffusion in a n–p–n structure was reduced, giving rise to a degradation of the thermal stability of this structure.

Growth of high quality epitaxial Si 1− x− yGe xC y layers by using chemical vapor deposition

The epitaxial quality of non-selective and selective deposition of Si 1− x− y Ge x C y (0≤ x≤0.30, 0≤ y≤0.02) layers has been optimized by using high-resolution reciprocal lattice mapping (HRRLM). The main goal was to incorporate a high amount of substitutional carbon atoms in Si or Si 1− x Ge x matrix without creating defects. The carbon incorporation behavior was explained by chemical and kinetic effects of the reactant gases during epitaxial process. Although high quality epitaxial Si 1− y C y layers can be deposited, lower electron mobility compared to Si layers was observed.

Quantitative Electron Diffraction Evidence for One-Dimensional Ordering in Magnetite above the Verwey Transition

Energy-filtered electron diffraction and three-dimensional reciprocal lattice mapping was used to study the nature of diffuse scattering in magnetite above the Verwey transition temperature. Characteristic Huang scattering associated with a single molecular polaron is observed at room temperature. As the temperature is lowered, the experiment shows narrowing of diffuse scattering in the (001) directions and additional ringlike diffuse scattering at q approximately 0.8, which suggests the presence of one-dimensional structures above the Verwey transition. Experimental measurements of temperature-dependent correlation lengths and diffuse scattering intensity indicate an increase in the number and length of the one-dimensional structure as the temperature is cooled toward the transition. This study demonstrates the electron sensitivity to atomic displacement and the quality of electron diffraction data for studying phase transition in complex materials.

Thermal strain in indium phosphide on silicon obtained by epitaxial lateral overgrowth

High-resolution x-ray diffraction reciprocal lattice mapping and low-temperature photoluminescence (PL) were used to study the thermal strain in InP layers grown on Si (001) substrate by hydride vapor-phase epitaxial lateral overgrowth (ELO) technique. Good agreement is found between the PL and x-ray measurements. We show that strain in the grown ELO InP/Si layers is affected by the aspect ratio (width to height ratio) of the ELO InP layer. Almost strain-free InP layer with high crystallographic quality is obtained on Si substrate, which is similar to that of a homoepitaxial InP layer.

Influence of doping on thermal stability of Si/Si 1− xGe x/Si heterostructures

The thermal stability of Si/Si 0.8Ge 0.2/Si npn and pnp structures grown by reduced pressure chemical vapor deposition has been studied. The influences of the diffusion of dopants in SiGe or adjacent layers on the thermal stability of the structure are also discussed. The thermal stability of the structures is shown to be dramatically increased compared to that of intrinsic layers when doping the strained Si 0.8Ge 0.2 layer with boron, phosphorus or arsenic. This performance is attributed to competition between dopant diffusion/precipitation phenomena and misfit dislocation development in the doped SiGe. Moreover, it is observed that doping only the Si buffer and cap layers in the Si/SiGe/Si structure also results in an enhancement in the thermal stability of the SiGe layer. Finally, when pnp or npn structures are grown, the structures exhibit significantly enhanced thermal stability. In addition, the boron out-diffusion from the SiGe layer is retarded in the sample where the Si buffer and cap layers were doped with phosphorus, presumably by in-diffusion of phosphorus into the SiGe layer. In this study, high-resolution X-ray reciprocal lattice mapping and secondary ion mass spectroscopy have been used as the main analysis tools.

Si 1−y C y / Si (001) gas-source molecular beam epitaxy from Si2H6 and CH3SiH3: Surface reaction paths and growth kinetics

In situ surface probes and postdeposition analyses were used to follow surface reaction paths and growth kinetics of Si1−yCy alloys grown on Si(001) by gas-source molecular-beam epitaxy from Si2H6/CH3SiH3 mixtures as a function of C concentration y (0–2.6 at %) and temperature Ts (500–600 °C). High-resolution x-ray diffraction reciprocal lattice maps show that all layers are in tension and fully coherent with their substrates. Film growth rates R decrease with both y and Ts, and the rate of decrease in R as a function of y increases rapidly with Ts. In situ isotopically tagged D2 temperature-programmed desorption (TPD) measurements reveal that C segregation during steady-state Si1−yCy(001) growth results in charge transfer from Si surface dangling bonds to second-layer C atoms, which have a higher electronegativity than Si. From the TPD results, we obtain the coverage θSi*(y,Ts) of Si* surface sites with C backbonds as well as H2 desorption energies Ed from both Si and Si* surface sites. θSi* increases with increasing y and Ts in the kinetically limited segregation regime while Ed decreases from 2.52 eV for H2 desorption from Si surface sites with Si back bonds to 2.22 eV from Si* surface sites. This leads to an increase in the H2 desorption rate, and hence should yield higher film deposition rates, with increasing y and/or Ts during Si1−yCy(001) growth. The effect, however, is more than offset by the decrease in Si2H6 reactive sticking probabilities at Si* surface sites. Film growth rates R(Ts,JSi2H6,JCH3SiH3) calculated using a simple transition-state kinetic model, together with measured kinetic parameters, were found to be in excellent agreement with the experimental data.

Selective Epitaxy of Si1 − xGex Layers for Complementary Metal Oxide Semiconductor Applications

The selective growth of structures on patterned substrates aimed for channel layer applications in a metal-oxide-semiconductor field effect transistor structure was investigated. By optimizing the growth parameters the surface roughness of these structures was reduced. Furthermore, selective epitaxy of high B- or P-doped SiGe layers for source/drain applications was also studied. Abrupt dopant profiles with a good epitaxial quality and low sheet resistances, e.g., 195 and 260 Ω/□ for 420 Å thick, B-doped and P-doped layers, respectively, were obtained. In this study, secondary ion mass spectroscopy, high-resolution reciprocal lattice mapping, atomic force microscopy, and cross-sectional transmission electron microscopy were used as the main characterization tools. © 2003 The Electrochemical Society. All rights reserved.

Characterization of epitaxial Si 1− yC y layers on Si(0 0 1) grown by gas-source molecular beam epitaxy

Epitaxial Si 1− y C y layers were grown by gas-source molecular beam epitaxy using Si 2H 6 (100%) and C 2H 2 (1% C 2H 2 in 99% He) between substrate temperatures of 600 to 700°C. Epitaxial Si 1− y C y films were obtained using C 2H 2 flow rates ranging from 0 to 1.0 sccm. Substitutional C atoms in the films were detected as the C local vibration mode (607 cm −1) in Raman and Fourier transform infrared absorption spectroscopy. The formation of the Si 1− y C y alloys was also confirmed by θ/2 θ measurements of X-ray diffractometry (XRD). The reciprocal lattice space map indicated the pseudomorphic growth of the Si 1− y C y layer on Si(0 0 1). The substitutional C content ( C s) was estimated using Vegard’s law and XRD data with a maximum C s of 0.96% obtained in a sample grown at 675°C. From the characterization of Si 1− y C y films annealed at temperatures between 700°C and 900°C, it was found that the thermal stability of the film strongly correlates with the initial C s content.

Aspect ratio dependent strains in InAs/InP quantum dots measured by synchrotron radiation x-ray diffraction

Uncapped self-assembled InAs quantum dots (QDs) grown on InP (001) were studied by synchrotron x-ray diffraction. Reciprocal lattice mapping of the (004) InAs peak shows the strain relaxation behavior with InAs coverage and coalescence at various growth conditions. The aspect ratio (height/diameter) of QDs increases linearly with decreasing strain in QDs in the perpendicular direction before complete strain relaxation by dot coalescence and misfit dislocation generation. The full widths at half maximum of InAs (004) peaks can be used to extract the average height of InAs QDs, which is in good agreement with that directly obtained by atomic force microscopy.

Structural studies of Fe0.81Ga0.19 by reciprocal space mapping

Reciprocal lattice mapping has been performed on Fe0.81Ga0.19 crystals by ω–ω/2θ, Ψ–φ, and ω–φ scans. A strong elongation of the 〈001〉c peak was found along the 〈110〉c direction. ω scans revealed short lateral correlation lengths ξ along 〈110〉c and strong diffuse scattering along the 〈001〉c. Multiple domains with monoclinic symmetry (angle ∼190°) were observed by Ψ–φ and ω–φ scans on the (001)c face, and were also tilted with respect to each other. The results show an average cubic structure with orthorhombic structural modulations, and two structural domain states that result in a limiting monoclinic symmetry.

X-ray diffraction studies of epitaxial laterally overgrown (ELOG) GaN layers on sapphire substrates

GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial lateral overgrowth (ELOG) mode were studied using the high-resolution X-ray diffraction technique in double and triple axis modes (including reciprocal lattice mapping), both in reflection and transmission geometries. GaN layer grown on unmasked sapphire was examined in the same way for a comparison. We have found that in the fully overgrown ELOG structures: (i) hexagonal unit cells are deformed, so the lattice parameters a ⊥ (perpendicular to the stripes) and a 30 (inclined by 30° to the stripes) are smaller by up to 0.1% and 0.02%, respectively, as compared to those in the GaN buffer, (ii) curvature radii of the samples are of 1.2–1.4 m in the direction parallel to the stripes and of 1 m in the direction perpendicular to the stripes, which is consistent with the strain observed, and (iii) sapphire miscut along the 〈11.0〉 direction (i.e. perpendicular to the stripes) causes an additional inclination of ELOG lattice planes with respect to those in the buffer. A qualitative explanation of these findings is presented taking into account increase of GaN grain size in the ELOG layers.

Estimation of bonded silicon-on-insulator wafers by means of diffractometry using a parallel X-ray microbeam

Crystallinity of bonded silicon-on-insulator (SOI) wafers has been investigated by means of diffractometry using a parallel X-ray microbeam. Peak shifts and extended tails were observed in the rocking curves of the SOI layer. Further, reciprocal lattice maps revealed that the SOI lattice planes were tilt dispersively within about 100 μrad. The typical sizes of the grains are ranging from a few μm to a several tens μm. The inferiority of the thin SOI crystal may arise from the extended force of buried oxide layer.

Phase stability, nitrogen vacancies, growth mode, and surface structure of ScN(0 0 1) under Sc-rich conditions

Rocksalt structure scandium nitride films have been grown on magnesium oxide (0 0 1) substrates by molecular beam epitaxy using a radio frequency plasma source for nitrogen. The case of Sc-rich growth conditions, which occurs when the scandium flux J Sc exceeds the nitrogen flux J N, is discussed. Despite the excess Sc during growth, reflection high-energy electron diffraction and X-ray diffraction (XRD) show that these films have only a single orientation which is (0 0 1), and ion channeling confirms the good crystallinity. Rutherford backscattering shows that these films are off-stoichiometric, and this is found to be directly related to variations in the nitrogen, not the scandium, content by secondary ion mass spectrometry. High-resolution XRD reciprocal lattice mapping shows that these variations in the nitrogen content are related to the existence of the N-vacancies. It is concluded that Sc-rich growth leads to the incorporation of N-vacancies into the crystal structure, the concentration of which depends on the Sc/N flux ratio. Additionally, excess scandium conditions at the surface are explored by in situ scanning tunneling microscopy. The observed wider terrace widths as compared to N-rich growth are due to an increased surface diffusion which is attributed to a Sc-rich, metallic surface structure. Combined with the large dislocation density, the enhanced diffusion results in a predominant spiral growth mode.

C lattice site distributions in metastable Ge1−yCy alloys grown on Ge(001) by molecular-beam epitaxy

Epitaxial metastable Ge1−yCy alloy layers with y⩽0.045 were grown on Ge(001) by solid-source molecular-beam epitaxy (MBE) at temperatures Ts=200–400 °C. Using calculated strain coefficients and measured layer strains obtained from high-resolution reciprocal lattice maps (HR-RLMs), we determine C lattice site distributions as a function of Ts and total C concentration y. HR-RLMs show that all as-deposited alloys are fully coherent with their substrates. Ge1−yCy(001) layers grown at Ts⩽350 °C are in a state of in-plane tension and contain C in substitutional sites, giving rise to tensile strain, as well as in nanocluster sites which induce negligible lattice strain. Ts=400 °C layers are strain neutral with negligible substitutional C incorporation. Increasing y and/or Ts leads to a decrease in substitutional C concentration, consistent with Raman spectroscopy results, with a corresponding increase in the C fraction incorporated in nanocluster sites. The latter suggests that nanocluster formation is kinetically limited during film deposition by the C–C adatom encounter probability at the growth surface. Overall, the results show that it is not possible by MBE to obtain fully substitutional C incorporation in Ge1−yCy(001) alloys, irrespective of y and Ts. This is consistent with ab initio density functional calculations results showing that C incorporation in nanoclusters sites is energetically favored over incorporation in substitutional Ge lattice sites. Annealing the Ge1−yCy(001) layers at Ta=550 °C leads to a significant decrease in the substitutional C fraction and, hence, lower tensile strain. Layers annealed at 650 °C are strain free as all substitutional C has migrated to lower-energy nanocluster sites.

Growth and characterization of phosphorus doped Si 1− yC y alloy grown by photo- and plasma-CVD at very low temperature

The properties of Si 1− y C y alloys grown on Si(001) by photo- and plasma-CVD are described. Epitaxial Si films were obtained by the addition of C 2H 2, CH 4 or SiH 2(CH 3) 2 to SiH 4 and H 2 gases at a substrate temperature of 200 °C by these two methods. Hydrogen incorporated in the epitaxial films during growth was observed to desorb on thermal annealing. The local vibration mode (607 cm −1) of C in Si was observed in the Raman spectra of films annealed at 700 °C. X-ray reciprocal lattice space mapping showed the Si 1− y C y alloys to be pseudomorphic. The highest substitutional C content of 3.5 at.% was obtained in the films grown with the addition of SiH 2(CH 3) 2. In-situ phosphorus doping was also carried out using PH 3. The electron concentration of Si 1− y C y films was lower than that of Si films grown at the same PH 3/SiH 4 ratio. However, the electron concentration was found to increase to the same level as Si films after annealing at 700 °C, to a magnitude of 5×10 18 cm −3. This result implies that dopant neutralization occurred in the as-grown Si 1− y C y films.