Plan-view Images Research Articles

Morphological and Compositional (S)TEM Analysis of Multiple Exciton Generation Solar Cells

Quantum confinement of charge carriers in semiconductor nanocrystals produces optical and electronic properties that have the potential to enhance the power conversion efficiency of solar cells. One of these properties is the efficient formation of more than one electron-hole pair from a single absorbed photon, in a process called multiple exciton generation (MEG). In this work we studied the morphology of nanocrystal multilayers of PbSe treated with CdCl2 using complementary imaging and spectroscopy techniques to characterise the chemical composition and morphology of full MEG devices made with PbSe nanorods (NRs). IN the scanning TEM (STEM), plan view images and chemical maps were obtained of the nanocrystal layers, which allowed for the analysis of crystal structure and orientation, as well as size distribution and aspect ratio. These results were complemented by cross-sectional images of full devices, which allowed accessing the structure of each layer that composes the device, including the nanorod packing in the active nanocrystal layer.

Direct insight into grains formation in Si layers grown on 3C-SiC by chemical vapor deposition

This work presents a structural study of silicon (Si) thin films grown on cubic silicon carbide (3C-SiC) by chemical vapor deposition. The presence of grains rotated by 90° around the growth direction in the Si layer is directly related to the presence of antiphase domains on the 3C-SiC surface. We were able to provide a direct evidence that the 90° rotation of Si grains around the growth direction occurs exactly on the termination of antiphase boundaries (APBs) in 3C-SiC layer. Increasing the 3C-SiC thickness reduces the APBs density on 3C-SiC surface leading to a clear improvement of the uppermost Si film crystal quality. Furthermore, we observed by high resolution plan-view TEM images the presence of hexagonal Si domains limited to few nm in size. These hexagonal Si domains are inclusions in small Si grains enclosed in larger ones rotated by 90°. Finally, we propose a model of grains formation in the Si layer taking into consideration the effect of the 3C-SiC thickness.

Focused Ion Beam Milling Technique for Plan-View TEM Sampling of DRAM Capacitor

As the semiconductor device feature size becomes smaller, the aspect ratio of DRAM capacitor gets higher. The higher the height of capacitor, the more storage node bent. Therefore, we adopt the Mechanically Enhanced Storage node for virtually unlimited Height (MESH) [1] process to prevent storage node’s bending nowadays. Nevertheless, the bending failure still exists, and thus we need to make a sample for physical failure analysis (PFA). Normally PFA needs a site specific transmission electron microscopy (TEM) sample which is vertically cross-sectioned by using focused ion beam (FIB) , but sometimes a plan-view TEM sample is also required to clarify the exact cause of failure. Figure 1-(a) shows the vertical TEM result of two bits failure caused by DRAM storage node’s bending. In the conventional plan-view TEM sampling process, the target height for plan-view TEM sampling is marked with ‘l’ shape marker [2] after realizing the height of node bridge as shown in figure 1-(b). It is important to know the end point during FIB milling [3]. And then, the top (red area) and bottom (yellow area) parts are removed to get the plan-view TEM sample. Figure 1-(c) is a TEM image after this plan-view TEM sampling process. The nodes do not stand in a line as you see in figure 1-(c). The nodes seem to move during the 3rd step milling (mill a bottom part) because of the void between nodes. The node may fall off a TEM thin foil sample in the worst case. In order to overcome this problem, we add a carbon deposition step right after the 2nd step of the top part milling as shown in figure 2-(a). As a result, we are able to get a plan-view TEM image where the nodes stand in a line as shown in figure 2-(b). Four major steps are, Step 1 : ‘1’ shape marking at the target height Step 2 : milling a top part of capacitor Step 3 : carbon deposition to fill the space between nodes Step 4 : milling a bottom part of capacitor We adopted this modified milling method to the TEM sampling of a real failure case and obtained a PFA result of a 2 bit failure using plan-view TEM image as shown in figure 2-(c). The new modified milling method turned out to be very effective and can be adopted in a mass production.

Structural features of indium antimonide quantum dots on the indium arsenide substrate

The properties of InSb/InAs quantum dots (QDs) have been investigated by transmission electron microscopy (TEM). Specific features of diffraction contrast were discovered in plan-view TEM images of big (9–10 nm in height and 38–50 nm in diameter) InSb QDs. To understand the origin of such distortions, a model of an InSb QD on InAs substrate containing a partial Frank dislocation (FD) was developed and used for calculations of the displacement field and the subsequent diffraction image simulation of an InSb QD for the first time. The shape of the QD was established to have an insignificant influence on the magnitude of radial displacements. The insertion of a misfit defect (a partial Frank dislocation) into the QD reduces the strain at the edges of the QD almost by 30%. The comparison of experimental and simulated data allowed us to explain the observed features of the moiré pattern in the image of a big InSb QD by the presence of a misfit defect at the QD-substrate interface.

N-face GaN/AlN/GaN/InAlN and GaN/AlN/AlGaN/GaN/InAlN high-electron-mobility transistor structures grown by plasma-assisted molecular beam epitaxy on vicinal substrates

Since on-axis GaN-on-sapphire substrates with low threading dislocation density are not available in the N-face orientation, we explored the growth of InAlN on vicinal (4° miscut along GaN GaN-on-sapphire substrates. The microstructure of In0.18Al0.82N layers grown by plasma-assisted molecular beam epitaxy at different temperatures was studied using scanning transmission electron microscopy (STEM). The cross-sectional and plan-view STEM images revealed lateral variations in the InAlN composition along (perpendicular to the step edges). Also, step bunching was observed in InAlN layers thicker than 10 nm. N-face high-electron-mobility transistor structures with lattice-matched InAlN backbarriers were then grown on these vicinal substrates with different InAlN thicknesses. Transmission line measurements showed that step bunching and lateral variation of InAlN composition degraded the two-dimensional electron gas (2DEG) mobility in the directions parallel and perpendicular to the steps. A 2DEG charge density of 1.1 × 1013 cm−2 and mobility of 1850 cm2 V−1 s−1 were achieved on a GaN/AlN/InAlN/GaN structure with 7.5 nm thick In0.18Al0.82N. By designing a double backbarrier (In0.18Al0.82N(7.5 nm)/Al0.57Ga0.43N(7 nm)), a 2DEG charge density of 2 × 1013 cm−2 and mobility of 1360 cm2 V−1 s−1 were attained, which resulted in a sheet resistance of 230 Ω/□.

Insights from STEM and NBED studies into the local structure and growth mechanism of misfit layered compounds prepared using modulated reactants

Abstract X-ray diffraction and transmission electron microscopy were used to probe the structure of the misfit compound [(SnSe)1.15]1(VSe2)1 grown using an elementally modulated precursor. The specular X-ray diffraction pattern contained only 00l reflections, which yielded a c lattice parameter of 1.203(1) nm. Cross-section STEM revealed alternating layers of SnSe and VSe2, in agreement with the structure model refined from the X-ray diffraction pattern using Rietveld refinement. Plan-view transmission electron microscopy revealed the in-plane grain structure of the films, yielding grain sizes in agreement with previously reported in plane X-ray diffraction studies and the cross-section STEM images. The plan view images also contained Moiré fringes resulting from grains with different relative tilting on both sides of interfaces as well as Moiré fringes resulting from different relative rotations between domains. An energy-filtered nano-beam electron diffraction pattern obtained from at least one domain in the [(SnSe)1.15]1(VSe2)1 sample investigated in cross section contained a series of resolvable supercell reflections along the c axis that indicated that the supercell c-axis lattice parameter was a multiple of three times that determined using X-ray diffraction. Energy filtered NBED of plan-view samples showed diffraction patterns from select regions with 12-fold symmetry, indicating that the arrangement of the layers is not rotationally random from layer to layer. This suggests that during the self-assembly of the amorphous modulated elemental precursor, the SnSe and VSe2 constituent layers must nucleate off the adjacent interfaces of the growing crystal, yielding layers that are locally rotationally aligned with growing crystal. Different processing conditions during the precursor to crystal self-assembly might enable the domain size and/or the extent of order to be controlled.

Marine habitat mapping of the Milford Haven Waterway, Wales, UK: Comparison of facies mapping and EUNIS classification for monitoring sediment habitats in an industrialized estuary

A detailed map and dataset of sedimentary habitats of the Milford Haven Waterway (MHW) was compiled for the Milford Haven Waterway Environmental Surveillance Group (MHWESG) from seafloor images collected in May, 2012 using sediment-profile and plan-view imaging (SPI/PV) survey techniques. This is the most comprehensive synoptic assessment of sediment distribution and benthic habitat composition available for the MHW, with 559 stations covering over 40km2 of subtidal habitats. In the context of the MHW, an interpretative framework was developed that classified each station within a ‘facies’ that included information on the location within the waterway and inferred sedimentary and biological processes. The facies approach provides critical information on landscape-scale habitats including relative location and inferred sediment transport processes and can be used to direct future monitoring activities within the MHW and to predict areas of greatest potential risk from contaminant transport.Intertidal sediment ‘facies’ maps have been compiled in the past for MHW; this approach was expanded to map the subtidal portions of the waterway. Because sediment facies can be projected over larger areas than individual samples (due to assumptions based on physiography, or landforms) they represent an observational model of the distribution of sediments in an estuary. This model can be tested over time and space through comparison with additional past or future sample results. This approach provides a means to evaluate stability or change in the physical and biological conditions of the estuarine system. Initial comparison with past results for intertidal facies mapping and grain size analysis from grab samples showed remarkable stability over time for the MHW.The results of the SPI/PV mapping effort were cross-walked to the European Nature Information System (EUNIS) classification to provide a comparison of locally derived habitat mapping with European-standard habitat mapping. Cross-walk was conducted by assigning each facies (or group of facies) to a EUNIS habitat (Levels 3 or 5) and compiling maps comparing facies distribution with EUNIS habitat distribution. The facies approach provides critical information on landscape-scale habitats including relative location and inferred sediment transport processes. The SPI/PV approach cannot consistently identify key species contained within the EUNIS Level 5 Habitats. For regional planning and monitoring efforts, a combination of EUNIS classification and facies description provides the greatest flexibility for management of dynamic soft-bottom habitats in coastal estuaries. The combined approach can be used to generate and test hypotheses of linkages between biological characteristics (EUNIS) and physical characteristics (facies). This approach is practical if a robust cross-walk methodology is developed to utilize both classification approaches. SPI/PV technology can be an effective rapid ground truth method for refining marine habitat maps based on predictive models.

Structural defects responsible for excessive leakage current in Schottky diodes prepared on undoped n-GaN films grown by hydride vapor phase epitaxy

Schottky diodes fabricated on undoped n-GaN films grown by hydride vapor phase epitaxy showed more than two orders of magnitude higher reverse current if the films contained open core defects. The open core defects were revealed by scanning electron microscope observation in secondary electrons, microcathodoluminescence (MCL), and electron beam induced current (EBIC) modes. Plan-view EBIC imaging showed that such films contained a relatively high density of large (∼10 μm in diameter) dark defects that were absent in good films with low leakage current. In plan-view scanning electron microscope images, pits with the density similar to the density of dark defects were observed. Cross-sectional MCL observation showed that the pits terminated the vertical micropipes starting near the interface with the substrate. Some of the micropipes closed approximately halfway through the grown thickness. The regions of micropipes, either closed or not, showed a higher intensity of bandedge and defect MCL bands. Possible reasons for the formation of such structures are discussed.

Lateral Gemanium Growth for Local GeOI Fabrication

Ge is a very attractive material for optoelectronic applications and for future CMOS technologies. Therefore the creation of Ge on Si with low defect density is of great interest. Several techniques to grow high quality Ge on Si are reported e. g. in combination with cyclic annealing and etching (1, 2) or using the aspect ratio trapping technique (3). In this study, the fabrication of local GeOI structures is demonstrated by filling a lateral cavity which was formed by selective sidewall etching (4) of a mesa-patterned SiO2 / Si layer on a SOI wafer. Lateral Ge growth is carried out by using a single wafer reduced pressure CVD system. For sample preparation, epitaxial Si is deposited. The thickness of the Si on buried oxide (BOX) is targeted to 430 nm. Then wet oxidation for 300 nm is performed to produce a 300 nm thick SiO2 cap on top of 300 nm thick Si on the BOX. Top SiO2 and Si on BOX are removed by RIE dry etching to form lateral Si (010) or Si (110) surfaces at the sidewall of a mesa structure. After that, the wafer is cleaned by standard HF-last RCA cleaning. The wafer is loaded into the epi. chamber and baked at 850oC in H2 to remove residual oxide on the Si sidewalls. Then selective etching of Si by HCl is performed to form a cavity in the SiO2. After the HCl etching, Ge is deposited selectively using a H2-GeH4-HCl gas mixture. SEM is used for characterization of the deposited Ge and TEM is applied for dislocation analysis. The strain distribution is analyzed by micro Raman spectroscopy at 514 nm laser wavelength. An angle view SEM image of the sample after HCl etching is shown in Fig. 1. By HCl etching Si between the BOX and the SiO2 cap is laterally removed. The thickness loss of the BOX and the SiO2 cap are negligible indicating that the Si etching process is highly selective to SiO2. No bending is observed at the floating part of the SiO2 cap layer. At the etchfront a Si (111) facet is formed by the lateral HCl etching. A cross section TEM image of the sample after HCl etching and selective Ge growth is shown in Fig. 2. The Ge layer is selectively grown laterally on the Si surface in the cavity formed by the HCl etching. Dislocations are densely located near the interface between Si and Ge. Aspect ratio trapping (3) also works for the lateral direction, resulting in a high crystal quality Ge layer growth after ~200 nm. In Figure 3, an AFM amplitude image of a 5 µm square mesa structure with [010] sidewall direction is shown after HCl etching and lateral Ge growth followed by the removal of the SiO2 cap by HF dip. The interface between Si and Ge is visible. The root mean square of the Ge surface roughness is ~0.4 nm. It is defined by the interface roughness between Si and the SiO2cap layer. In Figure 4, a plan-view TEM image of a 5 µm square mesa structure after HCl etching and lateral Ge growth is shown. A (113) facet is observed at the growthfront of Ge. Dislocation networks are located near the Si interface. Stacking faults run only parallel or perpendicular to the [110] direction. Between them a wide area without any dislocations toward the [010] direction is observed. These results demonstrate the feasibility of the fabrication of local GeOI with high crystal quality by an additional lithography and an etching process. References 1) Y. Yamamoto et al., Solid-State Electronics 60 (2011) 22) Y. Yamamoto et al., Thin Solid Films 520 (2012) 32163) J. S. Park et al., Appl. Phys. Lett. 90 (2007) 0521134) Y. Yamamoto et al. Thin Solid Films 517 (2008) 90

Atomic layer deposition of metal oxide patterns on nonwoven fiber mats using localized physical compression.

Patterning is an essential part of many industrial processes from printing to semiconductor manufacturing. In this work, we demonstrate a new method to pattern and selectively coat nonwoven textiles by atomic layer deposition (ALD) using compressive mask patterning. A physical mask combined with mechanical compression allows lateral definition and fidelity of the ALD coating to be controlled. We produce features of several sizes on different nonwoven fiber materials and demonstrate the ability to limit diffusion effects to within <200 μm of the pattern edge. Lateral and vertical penetration of reactive growth species into nonwoven mats is investigated by plan-view and cross-sectional imaging. Vertical growth is also analyzed by imaging coating depth into fiber mat stacks. We develop a fully quantitative transport model that describes well the effect of fiber structure and mechanical compression on the extent of coating under the physical mask. This method could be implemented for high-volume patterning for applications including flexible electronics.

Nanostructural defects for effective flux pinning in high-quality Bi2Sr2CaCu2O8+x epitaxial thin films with high critical current density

The dependence of the critical current density (Jc) and current–voltage (I–V) characteristics on the magnetic field H and temperature T were determined in c-axis-oriented epitaxial Bi2Sr2CaCu2O8+x (Bi2212) thin films prepared by metalorganic chemical vapor deposition. The films showed high Tc(R = 0) ≥ 83 K and high transport Jc > 1010 A m−2 at 10 K, but Jc decreased sharply when a magnetic field was applied in the c direction, except at low temperatures (≤20 K). The n-values (indices of the power-law I–V characteristics) decreased together with Jc, showing that the decrease is caused by thermally activated flux motion. To clarify the flux pinning mechanism operating in the films, nanostructural defects were investigated by transmission electron microscopy (TEM). Cross-sectional TEM images of the thin films revealed that the Bi2212 phase was twinned and that the twin boundary runs either parallel or perpendicular to the ab-plane depending on the region. We observed misfit dislocations at twin boundaries, and other dislocations associated with stacking faults parallel to the ab-plane, as well as anti-phase boundaries. Contrasts corresponding to dislocations parallel to the ab-plane and/or to the anti-phase boundaries were observed in plan-view TEM images, and nanoscale precipitates as observed in some YBa2Cu3O7−y (YBCO) films were almost entirely absent. The temperature dependence of low-field Jc, which was mostly unaffected by the thermally activated flux motion, approximately followed ∼(1−T/Tc)m(1+T/Tc)2 (m = 1.7–2.2). The temperature dependence with m ≈ 2, which can be explained by a simple theoretical model, was recently observed in YBCO thin films in which flux pinning was dominated by linear pins (partial dislocations surrounding stacking faults parallel to the ab-plane). From these results and theoretical considerations on the flux pinning force, we conclude that flux pinning in our Bi2212 films is mainly caused by dislocations parallel to the ab-plane and anti-phase boundaries.

Laboratory Investigation of the Impact of Lateral Spreading on Buoyancy Flux in a River Plume

AbstractThe relationship between lateral spreading and mixing in stratified gravity currents is investigated by comparing laterally confined and unconfined currents in a series of laboratory experiments. The vertical turbulent buoyancy flux is determined using a control volume approach with velocity and density fields derived from combined particle image velocimetry (PIV) and planar-laser-induced fluorescence (PLIF). Lateral spreading is determined in the unconfined experiments based on plan-view imaging using the optical thickness method (OTM). The authors find that lateral spreading dramatically modifies the plume structure; the spreading plume layer consists of approximately linear density and velocity profiles that extend to the surface, whereas the channelized plume profiles are uniform near the surface. Lateral spreading decreases the average plume density relative to laterally confined currents with similar inflow conditions. However, the local turbulent buoyancy flux in the spreading experiments is approximately equal to that in the confined experiments. This apparent paradox is resolved when the plume areas are taken into account. The total mixing integrated over the horizontal plume area is significantly higher in the spreading experiments. Thus, the experiments suggest that spreading does not appreciably alter the turbulent mixing processes at the base of the plume. However, it significantly increases the area over which this mixing occurs and, through this mechanism, increases the net dilution of river water at a fixed distance from the river mouth. Finally, the authors hypothesize that the spreading does not significantly increase the local turbulent buoyancy flux because spreading occurs preferentially near the surface, whereas buoyancy flux is greatest in the core of the current.

Nanocomposites of polyaniline and titania nanoparticles for gas sensors

Nanocomposite polyaniline (PANI) films with embedded TiO2 nanoparticles were prepared by electrochemical polymerization of aniline with titania added into the solution. The films were prepared for gas sensing applications. Their morphology and electrical resistivity were controlled by voltammetric parameters and aniline concentration. We found that the bottom auxiliary PANI film prepared by chemical polymerization in order to bridge the insulating gaps between the digits of interdigitated electrodes could be omitted because the nanocomposite film grew even in the gaps at certain monomer concentrations. The morphology and structure of the nanocomposites were studied by scanning and transmission electron microscopy, infrared spectroscopy and X-ray diffraction. FTIR spectra revealed the existence of chemical bonding between the nanoparticles and polymer chains. The films were tested for sensitivity to ammonia. We found that due to titania the sensitivity of the composite film increased two times reaching a 500% change in resistance at application of 100 ppm of ammonia. TEM plane-view image of a PANI-TiO2 nanocomposite film prepared by electrochemical polymerization of aniline with TiO2 nanoparticles added to the solution.

Texture and morphology developments of Yttria-stabilized zirconia (YSZ) buffer layer for coated conductors by RF sputtering

Yttria-stabilized zirconia (YSZ) films are deposited on CeO2/NiW tapes by RF sputtering for (Gd) BCO-coated conductors. Surface morphology and texture developments are investigated as the O2:Ar ratio and sputtering power increase. Both the grain size and the roughness of YSZ films increase as sputtering power increases. A simple model proposed by Bartelt et al. is used to explain the results. The strain relaxation mechanism plays a major role in the sudden increase in roughness for YSZ film deposited at a sputtering power of 50W. It is observed that low O2:Ar ratio favors the growth of (200) orientation for YSZ film, while high O2:Ar ratio favors the growth of (111) orientation. The preferential orientation (200) of the YSZ film with low O2:Ar ratio arises from template effect of CeO2 buffer layer. The (111) orientation of YSZ film with high O2:Ar ratio is due to thermodynamic mechanism aiming for the lowest surface energy. The grain size and roughness of our optimal YSZ film are 10–15nm and 0.7nm, respectively. The out-of-plane texture of our optimal YSZ film is 4.05°. The in-plane texture is 6.35°. The plan view and cross-section SEM images of YSZ films on CeO2/NiW tapes show a flat, dense and no micro-cracks morphology. Based on these results, (Gd) BCO films are deposited by RF sputtering, achieving self-field Jc of 4.0 MA/cm2 at 77K.

Nanoscale characterization of gold nanoparticles created by in situ reduction at a polymeric surface

Transmission Electron Microscopy is used as a quantitative method to measure the shapes, sizes and volumes of gold nanoparticles created at a polymeric surface by three different in situ synthesis methods. The atomic number contrast (Z-contrast) imaging technique reveals nanoparticles which are formed on the surface of the polymer. However, with certain reducing agents, the gold nanoparticles are additionally found up to 20 nm below the polymer surface. In addition, plan-view high-angle annular dark-field scanning transmission electron microscopy images were statistically analyzed on one sample to measure the volume, height and effective diameter of the gold nanoparticles and their size distributions. Depth analysis from high-angle annular dark-field scanning transmission electron microscopy micrographs also gives information on the dominant shape of the nanoparticles.

Plan-View and Cross-Sectional Photoluminescence Imaging Analyses of Threading Dislocations in 4H-SiC Epilayers

We performed a plan-view and cross-sectional photoluminescence (PL) imaging and a spectral analysis of threading dislocations in 4H-SiC epilayers in the near-infrared region. The bright PL spots of threading screw dislocations (TSDs) and threading edge dislocations (TEDs) observed in the plan-view PL imaging are compared with the grazing incidence synchrotron X-ray topography contrast, and precise discrimination of threading dislocations using the PL technique and the direct acquisition of Burgers vector directions of TEDs are demonstrated. The inclination angles of TSDs and TEDs across a thick epilayer are revealed by the cross-sectional PL imaging, and the variations in the plan-view PL appearances of the threading dislocations are confirmed to originate from the line directions of such dislocations.

Structure of Directly Bonded Interfaces Between Si and SiC

A Si-on-SiC wafer in which the Si wafer is directly bonded to the semi-insulating single-crystal 6H-SiC without an intermediate layer was developed. A remarkable improvement in the heat-dissipation performance due to the high thermal conductivity of SiC was demonstrated for Si metal oxide semiconductor field-effect transistors fabricated on the bonded wafers. In transmission electron microscopy (TEM), linear defects similar to misfit dislocations with a density of 2-6 × 107 lines/cm−2 were observed in plan-view TEM images of the Si/SiC interfaces. Comparison between Si(001)/6H-SiC(0001) and Si(111)/6H-SiC(0001) interfaces implies that the linear defects were formed on the Si side of the Si/SiC interface. Disordered Si layers with thicknesses of several atomic layers were observed in the cross-sectional TEM images, and the thickness is minimized at an annealing temperature of 1000{degree sign}C. The trap density at the interface was determined by admittance spectroscopy to be ~1 × 1011 cm−2eV−1 at most.

Characteristics of a-plane GaN films grown on optimized silicon-dioxide-patterned r-plane sapphire substrates

We report on the characteristics of a-plane GaN films directly grown on optimized silicon-dioxide-patterned r-plane sapphire substrates. Various shapes and sizes of silicon dioxide patterns were considered with the aim of achieving fully coalescent a-plane GaN films with a smooth surface and high crystalline quality. The omega full widths at half maximum of the (11–20) X-ray rocking curve values of optimized a-plane GaN films with regular hexagonal patterns of 1μm window width and 6μm mask width were measured to be 597arc sec along the c-axis direction and 457arc sec along the m-axis direction. Atomic force microscopy images revealed a significant reduction in the density of submicron pits in the mask region. Plan-view and cross-sectional transmission electron microscopy images showed that basal stacking faults and threading dislocation densities were reduced from ~5.7×105cm−1 and ~1×109cm−2 in the window region to ~1.8×105cm−1 and ~2.1×108cm−2 in the mask region, respectively.

Lattice and grain-boundary diffusions of boron atoms in BaSi2 epitaxial films on Si(111)

A 180-nm-thick boron (B) layer was deposited on a 300-nm-thick a-axis-oriented BaSi2 epitaxial film grown by molecular beam epitaxy on Si(111) and was annealed at different temperatures in ultrahigh vacuum. The depth profiles of B were investigated using secondary ion mass spectrometry (SIMS) with O2+, and the diffusion coefficients of B were evaluated. The B profiles were reproduced well by taking both the lattice and the grain boundary (GB) diffusions into consideration. The cross-sectional transmission electron microscopy (TEM) image revealed that the GBs of the BaSi2 film were very sharp and normal to the sample surface. The plan-view TEM image exhibited that the grain size of the BaSi2 film was approximately 0.6 μm. The temperature dependence of lattice and GB diffusion coefficients was derived from the SIMS profiles, and their activation energies were found to be 4.6 eV and 4.4 eV, respectively.

Lattice and grain-boundary diffusions of impurity atoms in BaSi2 epitaxial layers grown by molecular beam epitaxy

Al or B layers of a few hundreds of nm in thickness deposited on BaSi2 epitaxial films on Si(111) substrates were annealed at different temperatures, and the diffusion coefficients of Al and B were evaluated using secondary ion mass spectrometry with O2+. We also investigated the effect of post annealing (850°C, 10min) of BaSi2 films on the diffusion coefficients. It was found that both the lattice diffusion and the grain boundary diffusion were decreased by the post-annealing. The plan-view transmission electron microscopy images revealed that the grain size was increased from approximately 0.2 to 0.6μm by the annealing, and the X-ray diffraction intensities also increased. The activation energies of lattice and grain boundary diffusions in the post-annealed BaSi2 are 0.63eV and 0.58eV for Al, and 4.6eV and 4.4eV for B, respectively.