High-resolution Rutherford Backscattering Spectroscopy Research Articles

Rational Design of Monocrystalline (InP)yGe5–2y/Ge/Si(100) Semiconductors: Synthesis and Optical Properties

In this work, we extend our strategy previously developed to synthesize functional, crystalline Si(5-2y)(AlX)y {X = N,P,As} semiconductors to a new class of Ge-III-V hybrid compounds, leading to the creation of (InP)(y)Ge(5-2y) analogues. The compounds are grown directly on Ge-buffered Si(100) substrates using gas source MBE by tuning the interaction between Ge-based P(GeH3)3 precursors and In atoms to yield nanoscale "In-P-Ge3" building blocks, which then confer their molecular structure and composition to form the target solids via complete elimination of H2. The collateral production of reactive germylene (GeH2), via partial decomposition of P(GeH3)3, is achieved by simple adjustment of the deposition conditions, leading to controlled Ge enrichment of the solid product relative to the stoichiometric InPGe3 composition. High resolution XRD, XTEM, EDX, and RBS indicate that the resultant monocrystalline (InP)(y)Ge(5-2y) alloys with y = 0.3-0.7 are tetragonally strained and fully coherent with the substrate and possess a cubic diamond-like structure. Molecular and solid-state ab initio density functional theory (DFT) simulations support the viability of "In-P-Ge3" building-block assembly of the proposed crystal structures, which consist of a Ge parent crystal in which the P atoms form a third-nearest-neighbor sublattice and "In-P" dimers are oriented to exclude energetically unfavorable In-In bonding. The observed InP concentration dependence of the lattice constant is closely reproduced by DFT simulation of these model structures. Raman spectroscopy and ellipsometry are also consistent with the "In-P-Ge3" building-block interpretation of the crystal structure, while the observation of photoluminescence suggests that (InP)(y)Ge(5-2y) may have important optoelectronic applications.

Origins of unintentional incorporation of gallium in AlInN layers during epitaxial growth

We propose a mechanism of unintentional gallium (Ga) incorporation during the epitaxial growth of AlInN layers. We observed substantial amount of Ga in AlInN layers on GaN-free underlying layers and wafer carrier grown by metalorganic chemical vapor deposition, even though the Ga precursor was not introduced during the growth. The AlIn(Ga)N layers were characterized by high-resolution X-ray diffraction and Rutherford backscattering spectrometry. The mole fraction of Ga in the AlIn(Ga)N layers showed strong dependence on conditions of the growth chamber, making it difficult to maintain controlled alloy compositions only by growth process parameters. Also, Ga incorporation was not observed under the same growth parameters and conditions, when the indium (In) precursor was absent. The formation of In-Ga eutectic system between metallic Ga from the deposition on the chamber surrounding surfaces and adsorbed In is suggested as a possible mechanism for the Ga incorporation. Finally, we performed an intentional chamber coating process prior to growth of AlInN to achieve repeatable AlIn(Ga)N growth with stable alloy compositions.

高分解能ラザフォード後方散乱法の感度向上

高分解能ラザフォード後方散乱法の感度向上

Relaxation and critical strain for maximum In incorporation in AlInGaN on GaN grown by metal organic vapour phase epitaxy

Quaternary AlInGaN layers were grown on conventional GaN buffer layers on sapphire by metal organic vapour phase epitaxy at different surface temperatures and different reactor pressures with constant precursor flow conditions. A wide range in compositions within 30–62% Al, 5–29% In, and 23–53% Ga was covered, which leads to different strain states from high tensile to high compressive. From high-resolution x-ray diffraction and Rutherford backscattering spectrometry, we determined the compositions, strain states, and crystal quality of the AlInGaN layers. Atomic force microscopy measurements were performed to characterize the surface morphology. A critical strain value for maximum In incorporation near the AlInGaN/GaN interface is presented. For compressively strained layers, In incorporation is limited at the interface as residual strain cannot exceed an empirical critical value of about 1.1%. Relaxation occurs at about 15 nm thickness accompanied by strong In pulling. Tensile strained layers can be grown pseudomorphically up to 70 nm at a strain state of 0.96%. A model for relaxation in compressively strained AlInGaN with virtual discrete sub-layers, which illustrates the gradually changing lattice constant during stress reduction is presented.

Detailed analysis of the silicon surface under low-energy oxygen bombardment at atomic resolution

A detailed analysis of the amorphous-SiO${}_{2}$/crystalline-Si(011) interface formed by low-energy oxygen bombardment is performed by high-resolution Rutherford backscattering spectroscopy and spherical aberration-corrected scanning transmission electron microscopy (STEM). The atomic level analyses indicated a few nanometers of displaced Si atoms layer immediately below the synthetic SiO${}_{2}$ layer. A comparison between intensities of the high-angle annular dark field (HAADF) STEM image and the simultaneously acquired high-angle bright-field (HABF) STEM image shows that both intensities decreased at the existing layer of displaced Si atoms, and the relationship between these intensities cannot be explained by conventional image formation mechanisms. From detailed investigations using STEM imaging simulations, the HAADF STEM and HABF STEM images, which were simulated based on a realistic model, revealed the random distribution of a crystalline material and amorphous material at the interface; and this result agrees well with experimental results.

Solid phase epitaxy of ultra-shallow Sn implanted Si observed using high-resolution Rutherford backscattering spectrometry

We present detailed observations of the solid phase epitaxy process in Sn-implanted Si samples with nanometric depth resolution within a 50 nm ultra-shallow region beneath the surface. Measurements were made using high-resolution Rutherford backscattering spectrometry coupled with the ion channeling technique. Samples with Sn ions implanted onto Si substrates with and without prior Si+ self-amorphization implantation process show different crystal regrowth characteristics during annealing. Regrowth proceeds at a non-uniform rate up to a certain depth before stopping, and an Arrhenius-type defect density limiting model of crystal regrowth is proposed to account for this effect.

Materials science education: ion beam modification and analysis of materials

The Center for Irradiation of Materials (CIM) at Alabama A&M University (http://cim.aamu.edu) was established in 1990 to serve the University in its research, education and services to the need of the local community and industry. CIM irradiation capabilities are oriented around two tandem-type ion accelerators with seven beam lines providing high-resolution Rutherford backscattering spectrometry, MeV focus ion beam, high-energy ion implantation and irradiation damage studies, particle-induced X-ray emission, particle-induced gamma emission and ion-induced nuclear reaction analysis in addition to fully automated ion channeling. One of the two tandem ion accelerators is designed to produce high-flux ion beam for MeV ion implantation and ion irradiation damage studies. The facility is well equipped with a variety of surface analysis systems, such as SEM, ESCA, as well as scanning micro-Raman analysis, UV–VIS Spectrometry, luminescence spectroscopy, thermal conductivity, electrical conductivity, IV/CV systems, mechanical test systems, AFM, FTIR, voltammetry analysis as well as low-energy implanters, ion beam-assisted deposition and MBE systems. In this presentation, we will demonstrate how the facility is used in material science education, as well as providing services to university, government and industry researches.

Influence of multi-hit capability on quantitative measurement of NiPtSi thin film with laser-assisted atom probe tomography

Laser-assisted atom probe tomography (LA-APT) was applied to NiPtSi (0, 30, and 50% Pt contents) thin films on Si substrates. Consistent results with those of high-resolution Rutherford backscattering spectrometry (HR-RBS) were obtained. Based on the obtained data sets, the composition profiles from only the signals of single-hit events, meaning detection of one ion by one laser pulse, were compiled. The profiles from only the signals of multi-hit events, meaning detection of multiple ions by one laser pulse, were also compiled. There were large discrepancies with respect to Ni and Pt concentrations among the compiled profiles and the original profiles including the signals of both types of detection events. Additionally, the profiles compiled from single-hit events showed that Si concentration in NiPtSi layer became smaller toward the surface, differing from the original profiles and the multi-hit profiles. These results suggest that capability of simultaneous multiple-ion detection is important for appropriate LA-APT analyses.

Surface structures of equimolar mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy

Surface structures of equimolar mixtures of imidazolium-based ionic liquids (ILs) having a common cation (1-butyl-3-methylimidazolium ([C4MIM]) or 1-hexyl-3-methylimidazolium ([C6MIM])) and different anions (bis(trifluoromethanesulfonyl)imide ([TFSI]), hexafluorophosphate ([PF6]) or chlorine) are studied using high-resolution Rutherford backscattering spectroscopy (HRBS). Both cations and anions have the same preferential orientations at the surface as in the pure ILs. In the mixture, the larger anion is located shallower than the smaller anion. The [TFSI] anion is slightly enriched at the surface relative to [PF6] with coverage of ~60% for the equimolar mixtures of [C4(6)MIM] [TFSI] and [C4(6)MIM] [PF6]. No surface segregation is observed for [C6MIM] [TFSI]0.5[Cl]0.5 and [C6MIM] [PF6]0.5[Cl]0.5. These results are different from the recent TOF-SIMS measurement where very strong surface segregation of [TFSI] was concluded for the mixture of [C4MIM] [TFSI] and [C4MIM] [PF6].

High resolution Rutherford Backscattering Spectrometry investigations of ZrO2 layer growth in the initial stage on native silicon oxide and titanium nitride

High Resolution Rutherford Backscattering Spectrometry (HR-RBS) with a depth resolution of about 0.3nm near the surface was used to analyse the interface between ultrathin high-k ZrO2-layers and the substrate. In order to improve the quality of the analysis, a method was developed that takes local thickness variations, obtained by atomic force microscopy, into account during simulation of the HR-RBS spectra. The initial stages of atomic layer deposition (ALD) growth processes on Si(100) covered with native silicon oxide (SiO2) or with TiN have been studied. In the first case the interface is sharp, except for a small intermediate ZrSiO4-layer, and no diffusion of Zr-atoms in SiO2 could be detected. A quite different behaviour could be derived from high resolution spectra for the growth of ZrO2 on TiN. In addition, measurements of the surface topography of the TiN-layer revealed non-negligible surface roughness. Diffusion of Zr into polycrystalline TiN was demonstrated after correction for surface roughness. This observation indicates that already during the first ALD reaction cycle a small proportion of the deposited Zr-atoms diffuses – probably along grain boundaries – into the TiN-layer up to a depth of 3nm.

Effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy

The effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy was studied for 450keV He+ ions incident on ultrathin HfO2 films on Si. There was a tail at the low energy Hf edge in the observed spectrum. The tail increases with increasing HfO2 thickness and decreasing exit angle (exit angle with respect to the surface). A notable tail was observed even for HfO2 films of 2nm thickness at a small exit angle of 7°. The observed tail was reproduced by Monte Carlo simulations showing that the origin of the tail is multiple scattering. An analytical model was developed to estimate the tail for practical use. The derived analytical formula roughly reproduced the observed tail.

Tunnel Contacts for Spin Injection into Silicon: The Si-Co Interface with and without a MgO Tunnel Barrier—A Study by High-Resolution Rutherford Backscattering

In order to obtain high spin injection efficiency, a ferromagnet-semiconducor Schottky contact must be of high crystalline quality. This is particularly important in the case of ferromagnet-silicon interfaces, since these elements tend to mix and form silicides. In this study Co-Si (100) interfaces were prepared in three different ways: by evaporation at room temperature, low temperature (), and with Sb as surfactant, and their interface structures were analyzed by high-resolution RBS (HRBS). In all cases more or less strong in-diffusion of Co with subsequent silicide formation was observed. In order to prevent the mixing of Co and Si, ultra thin MgO tunnel barriers were introduced in-between them. In situ HRBS characterization confirms that the MgO films were very uniform and prevented the mixing of the Si substrate with deposited Co and Fe films effectively, even at .

Investigation of the factors determining the SIMS depth resolution in silicon-isotope multiple layers

In order to identify their controlling factors, the depth resolution parameters for secondary ion mass spectrometry, which include the decay length and the standard deviation of the Gaussian function (also referred to as the depth resolution function), for silicon atoms in a silicon matrix with silicon-isotope multiple layers were investigated under oxygen (O2+) and cesium (Cs+) ion bombardments with a wide ion energy range (from 200 eV to 10 keV) and with several incident angles. The use of silicon-isotope multiple layers in this investigation eliminated the chemical segregation effect caused by the sample composition. Measures were also taken to prevent ripple formation on the sputtered sample surface. The obtained depth resolution parameters were proportional to E1/2cos θ, where E is the primary ion energy per atom and θ is the incident angle relative to the surface normal. The relationships for decay length and standard deviation were different for the Cs+ ion, the O2+ ion with full oxidization, and the O2+ ion without full oxidization. The damage depth was measured by high-resolution Rutherford backscattering spectrometry and it was found that the relationships of the standard deviation versus damage depth depend only on the damage depth with a small dependence on the ion species (O2+/Cs+). The degree of mixing near the sputtered surface of thin silicon-isotope multiple layers bombarded by O2+/Cs+ ions was measured using laser-assisted atom probe analysis, and the relationship of the degree of mixing with the depth resolution parameters indicated that the decay length was degraded according to the degree of mixing. Atomic mixing/sputtering simulations revealed the factors determining the depth resolution parameters for secondary ion mass spectrometry. The standard deviation is found to be mainly degraded by the damage depth, which agrees with the results obtained by Rutherford backscattering spectrometry, whereas the decay length is mainly extended by the variance of the damage density profile, which is a parameter of the Gaussian function and governs the degree of mixing near the surface.

Nanosynthesis Routes to New Tetrahedral Crystalline Solids: Silicon-like Si3AlP

We introduce a synthetic strategy to access functional semiconductors with general formula A(3)XY (A = IV, X-Y = III-V) representing a new class within the long-sought family of group IV/III-V hybrid compounds. The method is based on molecular precursors that combine purposely designed polar/nonpolar bonding at the nanoscale, potentially allowing precise engineering of structural and optical properties, including lattice dimensions and band structure. In this Article, we demonstrate the feasibility of the proposed strategy by growing a new monocrystalline AlPSi(3) phase on Si substrates via tailored interactions of P(SiH(3))(3) and Al atoms using gas source (GS) MBE. In this case, the high affinity of Al for the P ligands leads to Si(3)AlP bonding arrangements, which then confer their structure and composition to form the corresponding Si(3)AlP target solid via complete elimination of H(2) at ∼500 °C. First principle simulations at the molecular and solid-state level confirm that the Si(3)AlP building blocks can readily interlink with minimal distortion to produce diamond-like structures in which the P atoms are arranged on a common sublattice as third-nearest neighbors in a manner that excludes the formation of unfavorable Al-Al bonds. High-resolution XRD, XTEM, and RBS indicate that all films grown on Si(100) are tetragonally strained and fully coherent with the substrate and possess near-cubic symmetry. The Raman spectra are consistent with a growth mechanism that proceeds via full incorporation of preformed Si(3)AlP tetrahedra with residual orientational disorder. Collectively, the characterization data show that the structuro-chemical compatibility between the epilayer and substrate leads to flawless integration, as expected for pseudohomoepitaxy of an Si-like material grown on a bulk Si platform.

Improvement of sensitivity in high-resolution ERDA

Recently, we have developed a new detector system for a magnetic spectrometer to reduce the background noise in high-resolution Rutherford backscattering spectroscopy. The detector system consists of a MCP detector for ion detection, which has a thin Mylar foil in front of the detector, and an electron detector to detect secondary electrons emitted by the ions upon impact on the Mylar foil. By measuring the ion signal in coincidence with the electron signal, the dark noise of the ion detector can be efficiently rejected. This new detector system is used to improve the sensitivity of high-resolution elastic recoil detection. The detection limit of 0.08 at.% is achieved for the boron depth profiling in Si.

Cluster effect on projected range of 30 keV [formula omitted] in silicon

Pre-amorphized silicon wafers are implanted with 30 keV C 60 + and 0.5 keV C + ions at room temperature with fluences about 2 × 10 15 atoms/cm 2. The depth profiles of implanted carbon are measured using high-resolution Rutherford backscattering spectroscopy. The observed average depth of C for the C 60 + implantation is 6.1 nm while that for the C + implantation is 4.0 nm, showing a large cluster effect on the projected range.

Structural and electrical characterization of HBr/O2 plasma damage to Si substrate

Silicon substrate damage caused by HBr/O2 plasma exposure was investigated by spectroscopic ellipsometry (SE), high-resolution Rutherford backscattering spectroscopy, and transmission electron microscopy. The damage caused by H2, Ar, and O2 plasma exposure was also compared to clarify the ion-species dependence. Although the damage basically consists of a surface oxidized layer and underlying dislocated Si, the damage structure strongly depends on the incident ion species, ion energy, and oxidation during air and plasma exposure. In the case of HBr/O2 plasma exposure, hydrogen generated the deep damaged layer (∼10 nm), whereas ion-enhanced diffusion of oxygen, supplied simultaneously by the plasma, caused the thick surface oxidation. In-line monitoring of damage thicknesses by SE, developed with an optimized optical model, showed that the SE can be used to precisely monitor damage thicknesses in mass production. Capacitance–voltage (C–V) characteristics of a damaged layer were studied before and after diluted-HF (DHF) treatment. Results showed that a positive charge is generated at the surface oxide–dislocated Si interface and/or in the bulk oxide after plasma exposure. After DHF treatment, most of the positive charges were removed, while the thickness of the “Si recess” was increased by removing the thick surface oxidized layer. As both the Si recess and remaining dislocated Si, including positive charges, cause the degradation of electrical performance, precise monitoring of the surface structure and understanding its effect on device performance is indispensable for creating advanced devices.

Improvement of sensitivity in high-resolution Rutherford backscattering spectroscopy

The sensitivity (limit of detection) of high-resolution Rutherford backscattering spectroscopy (HRBS) is mainly determined by the background noise of the spectrometer. There are two major origins of the background noise in HRBS, one is the stray ions scattered from the inner wall of the vacuum chamber of the spectrometer and the other is the dark noise of the microchannel plate (MCP) detector which is commonly used as a focal plane detector of the spectrometer in HRBS. In order to reject the stray ions, several barriers are installed inside the spectrometer and a thin Mylar foil is mounted in front of the detector. The dark noise of the MCP detector is rejected by the coincidence measurement with the secondary electrons emitted from the Mylar foil upon the ion passage. After these improvements, the background noise is reduced by a factor of 200 at a maximum. The detection limit can be improved down to 10 ppm for As in Si at a measurement time of 1 h under ideal conditions.

Trace element quantification in high-resolution Rutherford backscattering spectrometry

The potential of high resolution Rutherford Backscattering (RBS) for identification and quantification of created elements in thin films was investigated. A beam of 250 keV d + ions from the AN700 van de Graaff accelerator in Linz was used to characterize the composition of an organic multi-element compound, i.e. a thin film of dried human blood on a carbon substrate. It was possible to identify more than 10 chemical elements with high accuracy, in the absence of any matrix effects. For instance, the Fe concentration was determined with a relative error <3% (400 ± 10 ppm), in perfect agreement with standard blood test values. The detection limit of heavy elements with atomic number higher than Fe was found to be below 50 ppm.

高分解能RBS法による[CnMIM][TFSI]表面の分析

高分解能RBS法による[CnMIM][TFSI]表面の分析