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The divacancy (V2) is one of the fundamental defects in silicon. However, the interaction of V2 with hydrogen is still not fully understood. In the present work, deep level transient spectroscopy (DLTS) results on hydrogen-assisted annealing of V2 are presented. H+ ions were implanted with multiple energies into n-type Czochralski-grown samples, yielding uniform (box-like) concentration-versus-depth profiles of V2 and hydrogen in the region probed by the DLTS measurements. The evolution kinetics of V2 reveals two distinct processes: (i) a fast one attributed to dissociation of phosphorus-hydrogen pairs and reaction with highly mobile atomic Hi and (ii) a slow one whose origin is not identified yet. During the slow process, we observe the formation of a hydrogen-related electronic state, labeled E5* and positioned ∼0.42 eV below the conduction band edge. The growth of E5* displays a close one-to-one proportionality with the loss of a V2-related DLTS peak, presumably due to V2H, overlapping with that of the single negatively charged V2. [ABSTRACT FROM AUTHOR]

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are EC-0.06 eV (E42) and EC-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB configuration, where one H atom is directly bound to carbon in the anti-bonding position. [ABSTRACT FROM AUTHOR]

Injection-dependent lifetime spectroscopy of both n- and p-type, Cr-doped silicon wafers with different doping levels is used to determine the defect parameters of Cri and CrB pairs, by simultaneously fitting the measured lifetimes with the Shockley-Read-Hall model. A combined analysis of the two defects with the lifetime data measured on both n- and p-type samples enables a significant tightening of the uncertainty ranges of the parameters. The capture cross section ratios k=σn/σp of Cri and CrB are determined as 3.2 (-0.6, +0) and 5.8 (-3.4, +0.6), respectively. Courtesy of a direct experimental comparison of the recombination activity of chromium in n- and p-type silicon, and as also suggested by modelling results, we conclude that chromium has a greater negative impact on carrier lifetimes in p-type silicon than n-type silicon with similar doping levels. [ABSTRACT FROM AUTHOR]

We use Raman scattering to investigate the size distribution, built-in strains and the crystalline degree of Si-nanoclusters (Si-nc) in high-quality Si-rich oxynitride/SiO2 multilayered samples obtained by plasma enhanced chemical vapor deposition and subsequent annealing at 1150 °C. An initial structural characterization of the samples was performed by means of energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction (XRD) to obtain information about the cluster size and the presence of significant amounts of crystalline phase. The contributions to the Raman spectra from crystalline and amorphous Si were analyzed by using a phonon confinement model that includes the Si-nc size distribution, the influence of the matrix compressive stress on the clusters, and the presence of amorphous Si domains. Our lineshape analysis confirms the existence of silicon precipitates in crystalline state, in good agreement with XRD results, and provides also information about the presence of a large compressive stress over the Si-nc induced by the SiO2 matrix. By using the Raman spectra from low temperature annealed samples (i.e., before the crystallization of the Si-nc), the relative scattering cross-section between crystalline and amorphous Si was evaluated as a function of the crystalline Si size. Taking into account this parameter and the integrated intensities for each phase as extracted from the Raman spectra, we were able to evaluate the degree of crystallization of the precipitated Si-nc. Our data suggest that all samples exhibit high crystalline fractions, with values up to 89% for the biggest Si-nc. The Raman study, supported by the EFTEM characterization, indicates that this system undergoes a practically abrupt phase separation, in which the precipitated Si-nanoclusters are formed by a crystalline inner part surrounded by a thin amorphous shell of approximately 1-2 atomic layers. [ABSTRACT FROM AUTHOR]

X-ray photoelectron core level spectroscopy, secondary ion mass spectroscopy, spectroscopic ellipsometry, and extended x-ray absorption fine structure measurements have been employed to distinguish the effects of Al and N diffusion on the local bonding and microstructure of HfO2 and its interface with the Si substrate in (001)Si/SiOx/2 nm HfO2/1 nm AlOx film structures. The diffusion of Al from the thin AlOx cap layer deposited on both annealed and unannealed HfO2 has been observed following anneal in N2 and NH3 ambient. Both N2 and NH3 subsequent anneals were performed to decouple incorporated nitrogen from thermal reactions alone. Causal variations in the HfO2 microstructure combined with the dependence of Al and N diffusion on initial HfO2 conditions are presented with respect to anneal temperature and ambient. [ABSTRACT FROM AUTHOR]

Three-dimensional integration with through-silicon vias (TSVs) has emerged as an effective solution to overcome the wiring limit imposed on device density and performance. However, thermal stresses induced in TSV structures raise serious thermomechanical reliability concerns. In this paper, we analyze the near-surface stress distribution in a TSV structure based on a semi-analytic approach and finite element method, in comparison with micro-Raman measurements. In particular, the depth dependence of the stress distribution and the effect of elastic anisotropy of Si are illustrated to properly interpret the Raman data. The effects of the surface oxide layer and metal plasticity of the via material on the stress and Raman measurements are discussed. The near-surface stress characteristics revealed by the modeling and Raman measurements are important for design of TSV structures and device integration. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) of Si nanocrystals (Si-nc) embedded in fused silica has been investigated under simultaneous excitations by laser and low energy proton beam. Ionodegradation of the sample, characterized by a rapid decrease and a spectral blueshift of the PL emission has been observed. These effects are associated with the creation of non-radiative centers in the Si-nc. Micro-Raman spectroscopy analysis shows that the proton beam has not changed the average size of Si-nc, but has disturbed a fraction of Si-Si bonds inside the Si-nc, which is consistent with both simulations and direct measurements. A post-annealing performed at 400 °C for 1 h can restore the structural properties of the Si-nc, but only a part of their nominal PL emission intensity is recovered. Characterization of the damage induced by low energy proton irradiation reported in this paper makes the use of light ion beams relevant for the experimental investigation of nanostructured systems, such as ionoluminescence measurements. [ABSTRACT FROM AUTHOR]

We have developed an electrochemical method allowing an accurate determination of doping profiles in p-type silicon. Our approach is based on a precise and reproducible measurement of the anodization potential during the formation of porous silicon. The technique is tested on a reference sample with staircase doping profile ranging from 1017 to 1019 cm-3. It is shown that the depth resolution is readily linked to the doping level. For high doping concentrations, it approaches that of the secondary ion mass spectroscopy analysis with an estimated value of 60 nm/decade. [ABSTRACT FROM AUTHOR]

In situ reflection anisotropy spectroscopy (RAS)/reflection difference spectroscopy was applied as a quantitative probe of antiphase domains in heteroepitaxial films deposited on Si(100). The in situ probe was deduced from the spectroscopic signature of the P-rich, homoepitaxial GaP(100) surface and its well-established atomic reconstruction via a comparative investigation using RAS (homoepitaxial versus heteroepitaxial). For that, we determined changes in temperature, surface reconstruction, atomic order, and excess phosphorus on the surface of the homoepitaxial GaP(100) samples to specifically change the RA spectra in terms of shape and intensity. According to the presence of antiphase disorder a linear reduction in the RAS signal occurred. In addition, RA spectra of the heteroepitaxially prepared GaP/Si(100) films contained characteristic deviations from RA spectra of homoepitaxial GaP(100). They originated from reflections at the additional GaP/Si(100) heterointerface. Simple interference affecting the normalization of the RAS signal was found as a major source of the deviations and, thus, corresponding corrections were applied in the RA spectra. At photon energies around 3.2 eV, the correction even amplified the difference between the spectra of GaP/Si(100) and GaP(100) samples. This indicated an additional optical anisotropy induced by the interface reflection which peaked in the range of the determined spectral position. [ABSTRACT FROM AUTHOR]

We have explored defect annealing in radiation damaged silicon in a regime characterized by defect clusters and higher doping. Several types of pnp and npn Si bipolar transistors have been irradiated with ions and neutrons, then isochronally annealed from 300 to 600 K to study the evolution of deep level transient spectroscopy (DLTS) defect signatures. Variations in these data with radiation environment, Fermi level, annealing temperature, and doping density have been used to separate the contributions of three dominant defects to the DLTS defect spectra. We find that the normal Si divacancy and a divacancylike defect with similar properties make similar contributions to a DLTS peak normally associated with transitions from the single minus charge state of the divacancy. However the latter defect is clearly associated with the presence of defect clusters. The vacancy-donor center can also contribute to this high temperature DLTS signature, and its relative importance can be quantitatively assessed by varying doping density and the bias applied to the sample p/n junctions during annealing, and also by the observation that another, donor-related defect grows in as this center anneals. The ratio of vacancy-donor and vacancy-oxygen pairs appears to accurately follow that seen in earlier studies of gamma-irradiated Si. Discussions are presented concerning the effects of defect clustering on the structure, appearance, and evolution of the defects we have identified. [ABSTRACT FROM AUTHOR]

The capture cross sections of both electrons σn and holes σp were determined for interstitial molybdenum in crystalline silicon over the temperature range of -110 to 150 °C. Carrier lifetime measurements were performed on molybdenum-contaminated silicon using a temperature controlled photoconductance instrument. Injection dependent lifetime spectroscopy was applied at each temperature to calculate σp and σn. This analysis involved a novel approach that independently determined the capture cross sections at each temperature assuming a known defect density and thermal velocity. Since the energy state is in the lower half of the bandgap, the determination of σp is unaffected by the defect energy at all temperatures, and σp is found to decrease with temperature in a fashion consistent with excitonic Auger capture. At temperatures below 0 °C, the determination of σn is also unaffected by the defect energy due to the suppression of thermal emission, and σn decreases with temperature as well. It is shown that a projection of σn to higher temperature suggests the defect has an energy of 0.375 eV above the valance band edge of silicon. [ABSTRACT FROM AUTHOR]

Microwaves are used as a processing alternative for the electrical activation of ion implanted dopants and the repair of ion implant damage within silicon. Rutherford backscattering spectra demonstrate that microwave heating reduces the damage resulting from ion implantation of boron or arsenic into silicon. Cross-section transmission electron microscopy and selective area electron diffraction patterns demonstrate that the silicon lattice regains nearly all of its crystallinity after microwave processing of arsenic implanted silicon. Sheet resistance readings indicate the time required for boron or arsenic electrical activation within implanted silicon. Hall measurements demonstrate the extent of dopant activation after microwave heating of implanted silicon. Physical and electrical characterization determined that the mechanism of recrystallization in arsenic implanted silicon is solid phase epitaxial regrowth. The boron implanted silicon samples did not result in enough lattice damage to amorphize the silicon lattice and resulted in low boron activation during microwave annealing even though recrystallization of the Si lattice damage did take place. Despite low boron activation levels, the level of boron activation in this work was higher than that expected from traditional annealing techniques. The kinetics of microwave heating and its effects on implanted Si are also discussed. [ABSTRACT FROM AUTHOR]

We present in this study a spectroscopic investigation of spontaneous delamination of amorphous carbon nitride (a-CNx) films deposited on silicon substrates (Si) by rf magnetron sputtering of a graphite target in pure Ar/N2 gas mixture. The microstructural properties of the films were determined in their as-deposited state using infrared absorption and Raman spectroscopy experiments. Various shapes of debonding patterns have been observed. Based on the present experimental evidence, a description of nitrogen incorporation and the resulting hybridization states of the CN bonds in the a-CNx films prior and after delamination are proposed to elucidate the microstructural origin of this delamination occurring along the a-CNx/Si interface and the physicochemical mechanism that governed its dynamic. [ABSTRACT FROM AUTHOR]

We report the synthesis of spherical core-shell structures of silicon and silicon oxide by a novel route of forced external oxidation of ball milled silicon. Structural investigations reveal the formation of a crystalline silicon core surrounded by an amorphous oxide shell, with core and shell dimensions varying approximately between 4–10 and 55–170 nm, respectively. The observations suggest partial amorphization of crystalline silicon, invasive oxygen induced passivation of dangling bonds, and formation of different types of defects in the nanocrystalline silicon/silicon oxide core-shell structure, particularly at the interfaces. No detectable photoluminescence (PL) is obtained from the as-milled silicon, but the oxidized core-shell structures exhibit strong room temperature PL, detectable with unaided eye. The peak energy of the PL spectra blueshifts with an increase in excitation energy, with the peak positions varying from 2.24 to 2.48 eV under external excitation ranging from 2.41 to 3.5 eV. The observed PL characteristics are explained in terms of dominant electronic transitions between the localized defect states and quantum confinement induced widened band states. [ABSTRACT FROM AUTHOR]

Recently, there has been considerable interest in developing organically functionalized silicon surfaces for a variety of applications including sensing and nanoelectronics. In this study, a series of as-deposited, para-substituted aryl-diazonium molecular layers covalently grafted to <111>-orientation silicon are characterized using a variety of surface analysis techniques. Collectively, these measurements suggest that relatively ideal molecular layers can be achieved with a variety of headgroups. Submonolayer amounts of silicon oxide are detected on all modified surfaces and the extent of silicon oxidation depends on the molecular substituent. For electronic device applications, it is necessary to apply contacts to molecular layers while maintaining their structural and chemical integrity. To this end, in situ spectroscopies are used to infer the effects of metallization on such molecular layers. It is found that applying gold using a soft evaporation technique does not significantly perturb the molecular layer, whereas the application of copper using the same technique induces changes in the molecular vibrational spectra. Two complementary in situ spectroscopic methods are analyzed to more accurately determine the chemical properties of gold/molecule/silicon junctions. The physical mechanisms of the measurements and consequences for interpretation of the resulting spectra are discussed. [ABSTRACT FROM AUTHOR]

During electron-gun deposition of metal layers on semiconductors, the semiconductor is bombarded with low-energy metal ions creating defects in the outermost surface layer. For many years, it has been a puzzle why deep-level transient spectroscopy spectra of the as-deposited, electron-gun evaporated, n-type Schottky diodes are so simple displaying only one peak consisting of the merged E center and single-acceptor divacancy peaks, and no A center and double-acceptor divacancy peaks. With reference to a recent publication, we demonstrate that this is not due to a reduced production of divacancies and A centers in this situation but to the localization of these defects in highly defected regions. [ABSTRACT FROM AUTHOR]

Band bendings of Si substrates have been observed using hard x-ray photoemission spectroscopy. With a capability of collecting photoelectrons generated as deep as 40 nm, the binding energy shift in a core level caused by the potential profile at the surface of the substrate results in a spectrum broadening. The broadening is found to be significant when heavily doped substrates are used owing to its steep potential profile. The surface potential of the substrate can be obtained by deconvolution of the spectrum. This method has been applied to observe the band bending profile of metal-oxide-semiconductor capacitors with high-k gate dielectrics. By comparing the band bending profiles of heavily-doped n+- and p+-Si substrates, the interface dipoles presented at interfaces can be estimated. In the case of W gated La2O3/La-silicate capacitor, an interface dipole to shift the potential of -0.45 V has been estimated at La-silicate/Si interface, which effectively reduces the apparent work function of W. On the other hand, an interface dipole of 0.03–0.07 V has been found to exist at Hf-silicate/SiO2 interface for W gated HfO2/Hf-silicate/SiO2 capacitor. [ABSTRACT FROM AUTHOR]

The band alignment at the interfaces of Si(100) with amorphous (a-) and crystallized (c-) AlN layers was analyzed using internal photoemission and photoconductivity spectroscopy. The bandgap of thin a-AlN layers grown using atomic layer deposition is found to be 5.8±0.1 eV, widening to 6.5±0.2 eV after annealing induced crystallization into the wurtzite phase. Internal photoemission of electrons from the Si valence band to the AlN conduction band was found to exhibit the same energy threshold of 3.2±0.1 eV in amorphous and crystallized AlN. The energy band diagrams of a-AlN/Si(100) and c-AlN/Si(100) interfaces are established. [ABSTRACT FROM AUTHOR]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition (CBD) method. The optical properties of the grown ZnO nanorods were investigated by time resolved photoluminescence spectroscopy. It was found that the effective decay time of the near bandgap recombination in the CBD grown ZnO nanorods strongly depends on the diameter of the ZnO nanorods. Typically, the decay curves obtained from these ZnO nanorods show a combination of two exponential decays. The experimental results show that the fast exponential decay is related to the surface recombination and the slow decay is related to the “bulk” decay. The measured decay time of the effective surface recombination decreases with decreasing diameter, while the bulk decay time remains unchanged. The results also show that an annealing treatment around 500 °C significantly reduces the surface recombination rate. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. [ABSTRACT FROM AUTHOR]

Temperature-dependent lifetime spectroscopy allows for the determination of defect parameters (like ratio of the carrier capture cross sections and energy level) of pointlike defects in silicon. This necessitates reliable measurements of the low-level injection excess carrier lifetime. Photoluminescence-based measurement techniques have been shown to be ideal for this kind of measurements at room temperature, being immune to several measurement artifacts such as minority carrier trapping or depletion region modulation. In this article it will be shown how the effect of photon reabsorption influences the temperature-dependent photoluminescence measurements and how this can be accounted for using a theoretical model based on the generalized Planck equation. An intentionally titanium-contaminated silicon sample is investigated by means of temperature-dependent photoluminescence and injection-dependent photoconductance lifetime spectroscopy. Defect parameters of two independent recombination centers will be presented, which titanium introduces into the silicon band gap. One defect level at EC-0.24 eV agrees very well with a level found via deep-level transient spectroscopy measurements while another level at EC-0.49 eV could be measured for the first time using the advanced lifetime spectroscopic approach presented here. [ABSTRACT FROM AUTHOR]

Silicon samples H-implanted to a dose of 3×1016 cm-2 were analyzed by positron annihilation and ion backscattering techniques to investigate the growth of H-induced nanocavities at different annealing temperatures (400–900 °C). Positron annihilation lifetime spectroscopy revealed a constant increase in the vacancy cluster size (i.e., nanocavity size) as the annealing temperature increased. On the other hand, Doppler broadening and ion channeling measurements suggested strong interaction between the implanted H and the defects depending on the annealing temperature. Furthermore, Au-gettering experiments revealed that transient gettering sites are formed at 600 °C between the H projected range and the surface. These results indicated that H desorption is one of the key factors in the optimization of the gettering process with H-induced nanocavities. [ABSTRACT FROM AUTHOR]

The metamaterials (MMs) with planar metal arrays of split ring resonators were fabricated on quartz and silicon substrates; the influences of substrate permittivity and metal conductance on the magnetic responses of in the terahertz region were investigated. The electromagnetic (EM) responses of the metamaterials were characterized by terahertz time-domain spectroscopy. The experimental result reveals that there is a 0.39 THz redshift in the transmission spectra for the magnetic response when the substrate changes from quartz to silicon, which is in consistence with the finite-difference time-domain (FDTD) simulation. Based on the simulation and experimental results, and taking into account the EM properties of substrate materials, a modified L-C model is presented to understand the MM system in terahertz domain. [ABSTRACT FROM AUTHOR]

Hydrogenated microcrystalline silicon films (μc-Si:H) deposited at high deposition rates (∼2 nm/s) by means of the very-high-frequency (VHF) deposition technique in the high pressure depletion regime have been integrated into single junction p-i-n solar cells. It is demonstrated that μc-Si:H solar cells can be optimized using a twofold approach. First the bulk properties, deposited under steady-state plasma conditions, are optimized by monitoring the presence of crystalline grain boundaries in μc-Si:H. These hydrogenated crystalline grain boundaries can easily be detected via the crystalline surface hydrides contribution to the narrow high stretching modes by infrared transmission spectroscopy. The crystalline grain boundaries suffer from postdeposition oxidation which results in a reduced red response of the solar cell. The absence of these crystalline surfaces in an as-deposited μc-Si:H matrix reflects the device grade microcrystalline bulk material. Second, the prevention of silane backdiffusion from the background during the initial growth is a necessity to deposit a uniform μc-Si:H phase over the entire film thickness. The initial growth is optimized while preserving the optimized bulk properties deposited under steady-state conditions, using initial profiling of plasma parameters such as the silane flow and the VHF power density. Solar cell devices with efficiency of 8.0% at a μc-Si:H deposition rate of 2.0 nm/s are obtained using the presented approach. [ABSTRACT FROM AUTHOR]

Very thin Au layer was deposited on Si(100) using the sputtering technique. By annealing at 873 K Au/Si nanodroplets were formed and their self-organization was induced changing the annealing time. The evolution of droplet size distribution, center-to-center distance distribution, and droplet density as a function of the annealing time at 873 K was investigated by Rutherford backscattering spectrometry, atomic force microscopy (AFM), and scanning electron microscopy. As a consequence of such study, the droplet clustering is shown to be a ripening process of hemispherical three-dimensional structures limited by the Au surface diffusion. The application of the ripening theory allowed us to calculate the surface diffusion coefficient and all other parameters needed to describe the entire process. Furthermore, the AFM measurements allowed us to study the roughness evolution of the sputtered Au thin film and compare the experimental data with the dynamic scaling theories of growing interfaces. [ABSTRACT FROM AUTHOR]

This work reports on the crystallization of amorphous silicon (a-Si) films doped with 1 at. % of nickel. The films, with thicknesses ranging from 10 to 3000 nm, were deposited using the cosputtering method onto crystalline quartz substrates. In order to investigate the crystallization mechanism in detail, a series of undoped a-Si films prepared under the same deposition conditions were also studied. After deposition, all a-Si films were submitted to isochronal thermal annealing treatments up to 1000 °C and analyzed by Raman scattering spectroscopy. Based on the present experimental results, it is possible to state that (a) when compared to the undoped a-Si films, those containing 1 at. % of Ni crystallize at temperatures ∼100 °C lower, and that (b) the film thickness influences the temperature of crystallization that, in principle, tends to be lower in films thinner than 1000 nm. The possible reasons associated to these experimental observations are presented and discussed in view of some experimental and thermodynamic aspects involved in the formation of ordered Si–Si bonds and in the development of Ni-silicide phases. [ABSTRACT FROM AUTHOR]

We present the results of extensive modeling of hydrogenated amorphous silicon (a-Si:H) by combined ab initio molecular dynamics, an improved signal processing technique, and computer visualization, focusing on vibrational properties of a-Si:H. By comparing the theoretical and experimental vibrational spectra we correlate the hydrogen and silicon dynamics with the structural stability, bonding geometry, and diffusion in the a-Si:H material. Microscopic characteristics that cannot be obtained by other techniques, namely, hydrogen migration, bond switching, and silicon dangling bond passivation, are extracted from the atomic dynamics. We also demonstrate that this method offers the possibility of accessing other important macroscopic characteristics of a-Si:H and its stability in general. The approach we have developed can be used as well to model all aspects of a-Si:H dynamics, including the detrimental Staebler–Wronski effect. [ABSTRACT FROM AUTHOR]

The surface hydrogenated silicon nanocrystallites can be prepared by pulsed laser ablation of a silicon target in hydrogen background gas. Formation processes of the surface Si–H bonds were found by correlation between the surface structure of the deposited nanocrystal film and the time- and space-resolved spectra of plume emission during the deposition. A precursor of the hydrogenation is SiH species created in blast-wave stage by collision between ejected Si species and background hydrogen gas. Results of plume diagnostics indicate that the spatial or temporal separation between Si and SiH species is not an origin of the formation of the surface hydrogenated Si nanocrystallite. It is concluded that the correlation between the thermal stability of the Si–H bond and the temperature variation of the formed nanoparticle during the deposition is important for the formation of the chemical bonding on the surface. [ABSTRACT FROM AUTHOR]

This study examined the chemical interactions between an atomic-layer-deposited (ALD) HfO2 film and strained epitaxial Si1-xGex/Si (x=0.1,0.2,0.3) substrates during film deposition and postdeposition annealing (PDA), as well as their influence on the electrical properties. The influences of various predeposition surface treatments under O3 (POT) and NH3 (PNT) were also investigated in order to improve the understanding of the chemical and structural changes in thin film systems. Particular focus was made on the migration behavior of Si and Ge in the interface between a HfO2 film and Si1-xGex substrate, which critically affects the capacitance equivalent thickness (CET). The interdiffusion of the substrate elements during ALD and PDA could be controlled by POT and PNT. PNT was effective in reducing the diffusion of both Si and Ge during the ALD and PDA, whereas POT reduced only Si diffusion. The surface treatments reduced the changes in the CET after PDA without any significant increase in the leakage current density. The migration of the substrate elements was traced by secondary ion mass spectroscopy, auger electron spectroscopy, high-resolution transmission microscopy and x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions. [ABSTRACT FROM AUTHOR]

A series of shock-recovery experiments on a single crystal of silicon up to 38 GPa and characterizations of the recovered samples by x-ray diffraction analysis, Raman spectroscopy, and microscopic observations were performed for a better understanding of residual effects after shock loading by using a propellant gun. The x-ray diffraction trace of each sample revealed the absence of additional constituents including metastable phases and high-pressure phases of silicon except for 11 and 38 GPa. At 11 GPa, small amounts of metastable phases of silicon were obtained. The formation of copper silicide (Cu3Si) was confirmed in the sample shocked at 38 GPa. Considering the surface morphology revealed by microscopic observation, a thermochemical reaction through the melting of silicon resulted in the formation of Cu3Si. An additional band and the center frequency deviation of a peak were shown in the Raman spectroscopy results. The results of x-ray diffraction and Raman spectroscopy indicated that crystalline size reduction rather than the formation of metastable phases occurred. Structural deformation rather than the thermal effect caused by a shock-induced temperature rise may be responsible for the disappearance of metastable phases, which were observed in other high-pressure experiments. [ABSTRACT FROM AUTHOR]

Tritiated hydrogenated amorphous silicon (a-Si:H:T) thin films were deposited on crystalline silicon and high resistivity glass substrates. The time evolution of the density of defect states in these films was studied using the constant photocurrent method (CPM) and isothermal capacitance transient spectroscopy (ICTS). The density of defect states was found to change with time and to recover upon thermal annealing. The ICTS results revealed that, following thermal annealing, in a sample with approximately 1 at. % tritium, the concentration of positively charged dangling bonds (D+) decreased by more than an order of magnitude over a period of 300 h. The CPM results showed that, over the same period of time, the concentration of negatively charged dangling bonds (D-) increased by over two orders of magnitude. The D+ and D- concentrations followed exponential functions of time, but the rate was different than that of tritium decay. At the same time, the Urbach energy was found to decrease with time to about 1/2 of its postanneal value. The change in the D+ and D- concentrations is primarily the result of capture of the beta particle generated electrons in dangling bonds and weak bonds, with steady state achieved through the development of a balance between carrier generation and carrier capture processes. The role of excess carriers was confirmed by CPM experiments under electrical bias. [ABSTRACT FROM AUTHOR]

The authors investigate the effect of laser-induced heating on Raman measurements for different unpatterned and patterned substrates, including pure silicon, strained-silicon-on-insulator, and silicon-germanium layers on silicon. The relationship between heating and incident power of the laser used for Raman measurements is derived for unpatterned substrates, and the much stronger heating effects for line and island structures are shown. Additionally, the enormous heating of isolated silicon particles within the laser beam was investigated. The measured shifts clearly show that heating has to be considered even for moderate laser intensity when accurate stress measurements on such substrates are performed by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The variations of the low frequency noise versus temperature have been used to characterize the traps at the Si/SiO2 interface and in the depletion layer of partially depleted silicon on insulator metal-oxide-semiconductor field effect transistors obtained from recent 0.1 μm processes. For this technology, it is shown that 1/f noise and Lorentzians do not have the same physical origin. Moreover, an additional implantation, which is performed to control the short-channel effects, is shown to increase trap densities in the depletion layer and at the Si/SiO2 interface. [ABSTRACT FROM AUTHOR]

We studied the oxide charges and traps within nitrided Hf-silicate (HfSiON)/SiO2 gate stacks processed with high-temperature annealing with a spectroscopic technique by using high spatial resolution scanning capacitance microscopy. Spectroscopy was performed by detecting the static capacitance (dC/dZ) between a conductive probe and the sample while sweeping the sample bias. The dC/dZ image and spatially resolved dC/dZ-V spectrum revealed the existence of positive fixed charges within HfSiON and interface trap charges between the SiO2 underlayer and Si substrate. We also observed a transient electron trap process from the conductive probe to the HfSiON film as abrupt discontinuities in the dC/dZ-V spectrum and with bias-induced topography change of the HfSiON surface. These oxide charges and trap sites distribute inhomogeneously within HfSiON/SiO2 gate stacks, and the origin of these charged defects is ascribable to phase separation induced by high-temperature postdeposition annealing. [ABSTRACT FROM AUTHOR]

Optical properties of the fluorocarbon (FC) films plasma deposited on Si substrates are evaluated in this work using multiple sample analysis (MSA)-based spectroscopic ellipsometry (SE) with representing the film optical constants by the Forouhi-Bloomer (FB) and Tauc-Lorentz (TL) optical dispersions. This SE analysis supported also with other film investigations results in a two-layer optical model consisting of an interface assimilated to FC species-permeated Si layer beneath a surface smooth, homogeneous, and isotropic FC bulk film. Both dispersions yield a low-dielectric constant quality visible range refractive index of 1.39 and almost identical model layer thicknesses. Deposition-dominated linear film growth is thus asserted. Specifically, the FB dispersion better describes the region near absorption cutoff with taking up a lower optical band gap (OBG) than that of the TL dispersion, indicating thereby that particular FC film absorptions included in the FB dispersion are excluded in the other. Also, the FB index spectrum tends to peak towards a broad maximum in the ultraviolet (UV) wavelength range, whereas this trend is absent in the TL index spectrum probably removed by the TL parameter cross correlations although reduced by MSA. Sample to sample analysis further shows that the TL parameter correlation is accentuated by the instrument-limited UV range. The FB parameters are much less affected by cross correlation such that even the sample to sample analysis may be readily used in conjuncture with the FB dispersion for thicker FC films above 150 nm to monitor their index and OBG in tailoring desired film physical properties through deposition conditions. [ABSTRACT FROM AUTHOR]

Carrier dynamics in InGaN/GaN quantum wells (QWs) with compositional fluctuations is studied with time-resolved photoluminescence (PL) experiments and Monte Carlo simulations of exciton hopping and recombination. In particular, the effects of indium-rich nanoclusters in such a QW structure on the photon-energy-dependent PL decay time are investigated. In our experiments, two InGaN/GaN QW samples of different silicon doping conditions are used for demonstrating the two cases of different nanocluster densities. An increasing trend of PL decay time on the high-energy side of the PL spectrum is observed in the sample with high nanocluster density. Such a trend is not observed in another sample with few clusters. This difference is consistent with the simulation results which can help us in identifying the origin of the increasing trend as exciton trapping by the local potential minima in the spectral range of the free-carrier states. [ABSTRACT FROM AUTHOR]

High-pressure Raman and x-ray diffraxtion (XRD) measurements of a defect clathrate Ba8Ge43□3 have been carried out at room temperature up to 40 GPa. Three vibrational modes associated with guest Ba atoms were observed in the low-frequency region, and the structureless spectrum due to Ge vacancies was found in the framework vibrational region. The Raman spectra shows a pressure-induced phase transition at 8 GPa, which is due to the structural distortion through the three-bonded Ge atoms and to the change in the guest-host electronic interaction. Both Raman spectra and XRD patterns present the evidence for the amorphization of Ba8Ge43 around 30–40 GPa. The isostructural phase transition often present in intercalated silicon clathrates and associated with a large volume reduction was not observed for Ba8Ge43 up to 40 GPa. The pressure dependence of the lattice constant (a) normalized by a0 at 1 bar (a/a0) shows the continuous decrease with pressure until amorphization. From the good coincidence of this curve between Ba8Ge43 and Ba8Si46 at pressures above 15 GPa, we propose that the isostructural phase transition found for Ba8Si46 at 15 GPa may be originated from a defect-induced transformation to Ba8Si43□3 with the help of their theoretical equation of state by the first-principles calculations. [ABSTRACT FROM AUTHOR]

This investigation examines the extraordinary light transmission through periodic hexagonally ordered aluminum hole arrays on silicon substrates. The holes are circular and the arrays with various hole diameters were fabricated. The transmission spectra through the hole arrays were measured as a function of the incident angle of the light beam. It is observed that the transmission peak splits into two when the diameter of the hole is close to half of the lattice constant. At larger incident angles, the six degenerate (1,0) Al/Si surface plasmon modes split into four or three modes depending on the symmetry axis, and even higher order modes can be identified for small hole diameters. [ABSTRACT FROM AUTHOR]

The implantation profile of positrons emitted from a continuous energy spectrum source of 22Na in close proximity to a silicon target is modeled. The primary motivation is the use of positron lifetime spectroscopy to characterize layers of defects such as those created by ion irradiation, usually deemed accessible only to techniques which utilize slow positrons. The model combines the Makhov profile, used with considerable success to describe the profile of low energy (<30 keV) monoenergetic positrons, with the well-established, universal β-decay energy spectrum. The success of this approach is verified by measuring the fractions of positrons absorbed in thinned silicon samples. This verification utilizes lifetime measurements performed on silicon in a bilayer sandwich configuration with copper as a backing. The model accounts for the uncertainty in the positron backscattering at the silicon/copper interface. An optimal fit of the model to the experimental data requires that the parameter defining the mean depth of the Makhov profile (usually denoted r) is energy dependent. An example of application is provided in the form of a positron lifetime measurement of defects in silicon introduced by 1.5 MeV proton irradiation. Excellent agreement is found between the lifetime data and those obtained using a slow positron technique. [ABSTRACT FROM AUTHOR]

Temperature- and injection-dependent lifetime spectroscopy (TIDLS) as a method to characterize point defects in silicon with several energy levels is demonstrated. An intentionally cobalt-contaminated p-type wafer was investigated by means of lifetime measurements performed at different temperatures up to 151 °C. Two defect energy levels were required to model the lifetime curves on basis of the Shockley-Read-Hall statistics. The detailed analysis is based on the determination of the recently introduced defect parameter solution surface (DPSS) in order to extract the underlying defect parameters. A unique solution has been found for a deep defect level located in the upper band gap half with an energy depth of EC-Et=0.38±0.01 eV, with a corresponding ratio of capture cross sections k=σn/σp=0.16 within the interval of uncertainty of 0.06–0.69. Additionally, a deep donor level in the lower band gap half known from the literature could be assigned to a second energy level within the DPSS analysis at Et-EV=0.41±0.02 eV with a corresponding ratio of capture cross sections k=σn/σp=16±3. An investigation of the temperature dependence of the capture cross section for electrons suggests that the underlying recombination process of the defect in the lower band gap half is driven by a two stage cascade capture with an activation energy of ΔE=52±2 meV. These results show that TIDLS in combination with DPSS analysis is a powerful method to characterize even multiple defect levels that are affecting carrier recombination lifetime in parallel. [ABSTRACT FROM AUTHOR]

The structural properties and electrical characteristics of thin Nd2O3 gate oxides were deposited on silicon substrates by reactive rf sputtering. The structural and morphological features of these films were studied, as a function of the growth conditions (three various argon-to-oxygen flow ratios: 20/5, 15/10, and 12.5/12.5 and temperature from 600 to 800 °C), by x-ray diffraction, atomic force microscopy, and x-ray photoelectron spectroscopy. It is found that Nd2O3 dielectrics with a 12.5/12.5 ratio condition annealed at 700 °C exhibit a thinner capacitance equivalent thickness and excellent electrical properties, including the electric breakdown field, the interface trap density, the hysteresis, and frequency dispersion in the capacitance-voltage curves. This condition is suggested to the reduction of the interfacial SiO2 and silicate formation, and the small of surface roughness due to the optimization of oxygen in the metal oxide film. [ABSTRACT FROM AUTHOR]

Plasma-enhanced chemical vapor deposition phosphorus-doped silicon oxynitride (SiON) layers with a refractive index of 1.505 were deposited from N2O, 2% SiH4/N2, NH3, and 5% PH3/Ar gaseous mixtures. The PH3/Ar flow rate was varied to investigate the effect of the dopant to the layer properties. We studied the compositions and the chemical environment of phosphorus, silicon, oxygen, nitrogen, and hydrogen in these layers by using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The number of N–H and O–H bonds, which are responsible for optical losses around 1.55 and 1.3 μm, decreases in the as-deposited layers with increasing phosphorus concentration. Furthermore, the bonded hydrogen in all P-doped layers has been eliminated after annealing at a temperature significantly lower than required for undoped silicon oxynitride layers, that is to say 1000 °C instead of 1150 °C. The resulting optical loss in the entire third telecommunication window was well below 0.2 dB/cm, making P-doped SiON an attractive material for demanding integrated optics applications. [ABSTRACT FROM AUTHOR]

We describe unique methodologies for integration of InxGa1-xAs and GaAs1-xSbx semiconductor alloys with Si involving an innovative buffer layer approach based on lattice-engineered Ge1-ySny alloys. These are grown strain-free on Si(100) via formation of Lomer edge dislocations and exhibit a continuous selection of lattice parameters higher than that of Ge. This allows close lattice matching with the InxGa1-xAs and GaAs1-xSbx compounds, thereby providing a manifestly different approach to the integration of mismatched III-V semiconductors with silicon. A series of compositions across the entire alloy range were grown for both systems using metal organic chemical vapor deposition at low temperatures between 500–550 °C. The materials displayed high quality morphological, structural, and optical properties as evidenced by Rutherford backscattering spectroscopy, ion channeling, cross sectional transmission electron microscopy, atomic force microscopy, and photoluminescence characterizations. High resolution x-ray diffraction measurements indicated that the films grow with much less strain than those grown on conventional substrates. [ABSTRACT FROM AUTHOR]

The hydrogenation of crystalline Si by methods used to passivate defects in Si solar cells has been studied by infrared spectroscopy. For these experiments, floating-zone Si that contained Pt impurities that act as traps for H was used as a model system in which H could be directly detected. In this model system, the concentration and indiffusion depth of H were determined for different hydrogenation treatments so that their effectiveness could be compared. The postdeposition annealing of a hydrogen-rich SiNx surface layer was found to introduce H into the Si bulk with a concentration of ∼1015 cm-3 under the best conditions investigated here. [ABSTRACT FROM AUTHOR]

Silicon nanocrystals, average sizes ranging between 3 and 7 nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction (XRD). Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800 °C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix. [ABSTRACT FROM AUTHOR]

Schottky contacts on p-type silicon, with embedded arrays of β-FeSi2 nanocrystallites, were studied by current-voltage (I-V), deep level transient spectroscopy (DLTS), and low-frequency noise measurements. Forward I-V characteristics on logarithmic scale indicate that space-charge limited current (SCLC) dominates the carrier transport in these diodes. From an analysis of the SCLC characteristics, we found that two arrays of β-FeSi2 nanocrystallites induce a trap level at 320 meV above the valence band edge with concentration of 5×1014 cm-3, which is in relatively good agreement with the trap detected by DLTS. By inserting ten arrays of β-FeSi2 nanocrystallites, two trap levels at 300 and 340 meV with concentrations of 2.6×1014 and 1.1×1015 cm-3, respectively, were found from the SCLC analysis. By increasing the number of the inserted arrays of β-FeSi2 nanocrystallites from 2 to 10, a trap at 402 meV with concentration of 6.5×1015 cm-3 has been detected by DLTS, failing to detect the second trap observed by SCLC measurements. The normalized power spectral density SI/I2 vs V exhibits a peak at the transition voltage from the trap-filling regime to the SCLC regime, corresponding to a deep trap level. It is demonstrated that the noise technique is more sensitive than the SCLC and DLTS techniques in extracting information about the deep trap parameters. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry (SE) in the visible/near-UV spectral range is applied to monitor optical critical dimensions of quartz, Si, and Ta gratings, namely, the depth, linewidth, and period. To analyze the SE measurements, the rigorous coupled-wave theory is applied, whose implementation is described in detail, referred to as the Airy-like internal reflection series with the Fourier factorization rules taken into account. It is demonstrated that the Airy-like series implementation of the coupled-wave theory with the factorization rules provides fast convergence of both the simulated SE parameters and the extracted dimensions. The convergence properties are analyzed with respect to the maximum Fourier harmonics retained inside the periodic media and also with respect to the fineness of slicing imperfect Ta wires with paraboloidally curved edges. [ABSTRACT FROM AUTHOR]

The microstructure of Si/Ti/Al/Ni/Au was investigated using transmission electron microscopy and energy dispersive x-ray spectroscopy. The dependence of the contact resistance on the silicon layer thickness and the temperature was correlated to the microstructure of the alloyed contacts. The enhancement of the contact resistance by inserting a 30 Å thick Si layer under the Ti/Al/Ni/Au metallization was attributed to diffusion of the contact into the AlGaN layer. Increasing the Si thickness and or the temperature resulted in the formation of Gold (Au)-based silicides, which prevent the formation of low interfacial TiN or AlN layers. [ABSTRACT FROM AUTHOR]

Raman spectroscopy finds applications in many research fields to monitor stress on a micrometric scale. Unfortunately, the interpretation of Raman maps is always complicated by the tensorial nature of stress and by averaging effects due to the finite spatial resolution of the technique. Usually, the interpretation is either purely qualitative or based on thorough simplifications. In this paper we present an approach that compares the experimental data with a virtual experiment using a finite-element model. The method is applied to the study of the stress generated in a microelectronic device during the manufacturing process. The results are used both as a feedback and a validation for the modeling and also for the interpretation of the Raman data. [ABSTRACT FROM AUTHOR]

Micro-Raman spectroscopy and atomic force microscopy investigations have been applied on hydrogen implanted p-type Czochralski silicon samples to investigate the hydrogen related defects and their evolution after subsequent annealing. The thermal evolution of interstitial-hydrogen and vacancy-hydrogen complexes and hydrogen terminated silicon dangling bonds has been analyzed. Furthermore, the two Raman lines of molecular hydrogen attributed to free hydrogen molecules in blisters and molecular hydrogen trapped in multivacancies have been observed and analyzed. A mechanism based on the exchange of the hydrogen atoms between different hydrogen related defects during the annealing is proposed for the blister formation process, which is relevant for the hydrogen induced exfoliation for silicon-on-insulator fabrication. [ABSTRACT FROM AUTHOR]