bluuebunny/crossref_metadata_2025 huggingface dataset:
The Luminescence Mechanism of Porous Silicon
Authors: Calcott P. D. J. , Nash K. J. , Canham L. T. , Kane M. J. , Brumhead D.
Published: March 2011

We report resonantly excited photoluminescence (PL) spectroscopy of highly porous silicon. In the PL spectra we observe satellite structure due to the participation of momentum-conserving phonons in the optical transitions. The momentum-conserving role of these phonons, together with their energies and relative coupling strengths, demonstrate beyond doubt that crystalline silicon, which has already been shown to be the dominant constituent of unoxidised porous silicon, also forms the luminescent material. We show that the theory of quantum confinement in crystalline silicon wires can explain our results and those of other experiments, if the electron-hole interaction, andthe localisation of carriers by fluctuations in wire width, are taken into account.
Optical Properties and New Functionality of Nanocrystalline CuCl and Ge
Authors: Masumoto Yasuaki
Published: March 2011

Lasing of nanocrystalline CuCl embedded in a NaCl single crystal wasobserved for the first time. Lasing takes place at 77 K in nanocrystalline CuCl sandwiched between dielectric mirrors under the pulsed ultraviolet laser excitation. The lasing transition is that from bi-exciton to exciton. The lasing is observed up to 108 K. The optical gain of nanocrystalline CuCl is almost the same as that of bulk crystals in spite of the low concentration of CuCl in the NaCl matrix.

The origin of visible photoluminescence of nanocrystalline Ge in SiO2 glassy matrix has been studied. Spectroscopic analyses of nanocrystalline Ge indicate that the room-temperature photoluminescence comes from nanocrystalline Ge of diameter of 4 nm or less. High-resolution electron microscopic studies imply that the structure of nanocrystalline Ge of diameter ≤ 4 nm differs from the diamond structure. These data suggest that new nanostructure crystalline Ge having a character of direct optical transition exhibits the visible photoluminescence.
ESR Study of Porous Silicon
Authors: Cheung W. Y. , Wong S. P. , Wilson I. H. , Kan C. F. , Hark S. K.
Published: March 2011

A detailed ESR study has been performed on porous silicon on both <100> and <111> p-type silicon substrates prepared using anodization in HF under a range of conditions and the results are correlated with the light emission properties. It is found that the ESR spectra are dependent upon the orientation of the samples. The ESR defect centers are identified to be the Pb centers or Pbo centers of the Si-SiO2 system from the g-value anisotropy maps. The variation of the spin density Ns with annealing conditions has also been studied for samples annealed either in nitrogen or oxygen ambient at 200°C for various time intervals. It is concluded that the increase or decrease of Ns are due to the generation or elimination of the Pb or Pbo centers in conjunction with the oxidation process during annealing. From PL study of these samples, it is found that there is no simple correlation between the spin density and the PL intensity. However, a blue shift in the PL peak position was observed both in samples after a post-annealing etch in HF solution, and in samples annealed in oxygen without a post-annealing etch. This blue shift supports the quantum confinement model of light emission from porous silicon.
Observation of Paramagnetic Silicon Dangling Orbitals in Luminescent Porous Silicon
Authors: Rong F. C. , Poindexter E. H. , Harvey J. F. , Morton D. C. , Lux R. A. , Gerardi G. J.
Published: March 2011

We have detected two dominant paramagnetic centers in porous silicon by electron paramagnetic resonance (EPR). One of them is isotropic, assigned to a defect in amorphous silicon oxide in the porous silicon layer. The other is anisotropic, and is very much like a Pb center at a planar Si/SiO2 interface. This EPR center is unambiguously identified as an •Si≡Si3 moiety, a silicon with dangling orbital, back-bonded to three silicon atoms, by 29 Si hyperfine structure (HFS) associated with the dangling orbital, and 29 Si superHFS from three neighboring silicon atoms, as similarly observed in the usual planar surface Pb structure. The dangling orbitals are highly localized and heavily p character. The disposition of dangling orbitals is evidence that the skeletal structure of luminescent porous silicon is crystalline and has a lattice which is aligned and continuous with the wafer substrate. The possibility that these centers are the major photoluminescent killers or quenchers is not supported by our hydrogen annealing experiments.
High Spatial Resolution Mapping of Porous Silicon
Authors: Ettedgui E. , Peng C. , Tsybeskov L. , Gao Y. , Fauchet P. M. , Carver G. E. , Mizes H. A.
Published: March 2011

Porous silicon (PSI) samples with high photoluminescence (PL) efficiency were examined using microscopic mapping techniques including scanning election microscopy (SEM) and spatially resolved photoluminescence (SRPL). Studies of the growth conditions indicate that the homogeneity of the PL and the surface roughness of the sample depend on the preparation procedure of the PSI layer. SEM and spatially-resolved reflectance scans of an n-type sample with a PSI layer on the order of 100 μm reveal a highly fractured surface. SRPL of the same sample shows non uniform PL on a scale of 5 μm. Cross-sectional analysis of the samples with SRPL and SEM reveals the intricate multilayer structure of the PSI film. The top portion of the PSI film is largely responsible for the PL and is composed of isolated column-like structures. We have also observed cross-shaped structures reminiscent of stress fractures on the surface of PSI films using SEM or optical microscopy. Furthermore, atomic force microscopy (AFM) and SEM measurements of the surface of PSI films of intermediate thickness reveal that samples which appear smooth on ̃ lμm scale are actually covered with clumped structures on the order of 100 to 150 nm.
Porous Silicon Photoluminescence Versus HF Etching: No Correlation with Surface Hydrogen Species
Authors: Robinson M. B. , Dillon A. C. , George S. M.
Published: March 2011

The photoluminescence and infrared absorbance of electrochemically anodized porous silicon samples were examined as a function of hydrofluoric acid (HF) etching time. Transmission FTIR spectroscopy measurements revealed that the infrared absorbance from silicon hydrogen surface species was largest for the initial porous silicon samples and immediately decreased with HF etching. In contrast, the photoluminescence did not appear until after HF etching times of 20–80 minutes, depending on initial sample porosity. Subsequently, the photoluminescence intensity increased, reached a maximum, and then progressively decreased versus HF etching time. These HF etching results demonstrate that there is no direct correlation between the photoluminescence and the silicon hydrogen surface species.
Electron Spin Resonance Investigations of Rapid Thermal Oxidized Porous Silicon
Authors: Linke H. , Omling P. , Meyer B. K. , Petrova-Koch V. , Muschik T. , Lehmann V.
Published: March 2011

We studied the defect properties present in rapid thermal oxidized porous silicon (RTOPS) by Electron Spin Resonance (ESR). Two different types of defects are distinguished, one similar to the ones observed in damaged c-Si, and in a-Si. The second one is probably related to the Pbo center at the Si/SiO2 interface. The minimum density of 1016 cm-3 is observed for the as etched and for the 900°C oxidized samples, but reaches a maximum of 8×1018 cm-3for the 600°C samples. The PL intensity anticorrelates with the defect densities, which shows that nonradiative recombination via defects is a very powerful channel in quenching the PL efficiency.
Formation Mechanism of Microporous Silicon: Predictions and Experimental Results
Authors: Lehmann V. , Gösele U.
Published: March 2011

Recently we presented a formation mechanism for micro-porous silicon which is based on a depletion of holes in the porous region due to quantum confinement. This theory allows predictions concerning the dependence of the porous morphology on the formation conditions. It is the purpose of this work to check whether these predictions are in accordance with experimental observations.
Effect of Laser Illumination on Oxidization of Porous Silicon
Authors: Zhang L. Z. , Mao J. C. , Zhang B. R. , Zhu W. X. , He Y. L. , Song H. Z. , Duan J. Q. , Qin G. G.
Published: March 2011

We have studied the effect of laser illumination (argon laser line of 488 nm) on the oxidization process of the inner surfaces of porous silicon (PS) by measuring the photoluminescence (PL), Fourier-transform infrared (FTIR) absorption and x-ray photoelectron spectroscope and contrasted the variations of PL and FTIR spectra of the PS treated in the following four ways: 1. In vacuum with laser illumination (LI) with power density of 12 mW / mm2. 2. In oxygen with LI. 3. In oxygen without LI. The times for all the above three treatments were 1 h. 4. Storage in air for 2 months without LI. The PL peak of PS showed serious degradation and a blue shift in case 2 but only a moderate degradation and no shift in case 1. The results of FTIR absorption show that the LI in an atmosphere of oxygen enhanced greatly the increase of oxygen-related absorption bands and the decrease of various silicon-hydrogen vibrational mode absorption bands.
Mechanism of in-Situ Photoluminescence Decay in Porous Silicon and its Application to Maskless Patterning
Authors: Takai Mikio , Indou Sanae , Murase Hisanori
Published: March 2011

PL decay in a time scale of ms for fresh porous Si surfaces was investigated for different atmospheres and excitation intensities to clarify the mechanism of the PL decay. The PL excitation intensity and atmosphere were found to affect the decay of PL, which was due to laser enhanced oxidation.

Locally PL excited areas of porous Si were also found to be etched in a HF solution. Maskless patterning using this effect could be performed by a scan of a focused laser beam followed by HF etching.
Brønsted and Lewis Base Quenching of Photoemission from Luminescent ‘Porous Silicon’: Surface Protons in the Luminescence Mechanism
Authors: Chun J. K. M. , Bocarsly A. B. , Cottrellt T. R. , Benzigert J. B. , Yee J. C.
Published: March 2011

The photoluminescence (PL) observed from porous silicon (PS) is found to be very sensitive to pH. Brønsted bases quench the PL and simultaneously produce a blue shift of the p-type PS emission. Similarly, PL of n-type PS is quenched, but the emission is red shifted. Exposure to acids enhances PL and reverses the quenching due to base exposure. A pKa of 3–4 was determined for PS formed on both n- and p-type substrates, and identifies an acidic surface proton as a primary component in the PL mechanism. Variations in the intensity and energy distribution of PL as a function of temperature suggest that: 1) small changes in the hydration state of the surface may affect the emission, and 2) at least two luminescent species exist on the surface of PS; one of which is pH and temperature sensitive. SO2, a Lewis base, also quenches the PL of p-type PS quickly and reversibly. Exposure to acid is unnecessary for restoration of the PL. In contrast to reactivity with Brønsted bases, the reversibility with SO2 argues for a different quenching mechanism. Preliminary experiments show that PL is significantly quenched, ∼2–5%, by concentrations of ∼30ppm SO2 in Ar.
Visible Photoluminescence and Microstructure of Annealed and Chemically Etched Amorphous Si
Authors: Jung K. H. , Shih S. , Kwong D. L. , Cho C. C. , Gnade B. E.
Published: March 2011

We have studied the visible photoluminescence (PL) and microstructure of porous Si layers (PSLs) fabricated by the chemical etching of annealed amorphous Si (a-Si). The a-Si layers were partially crystallized by annealing between 550°C-1150°C in N2 and the PSL formed by etching in a HF-HNO3-based solution. No visible PL was observed after etching of unannealed a-Si. Visible PL was detected after etching a-Si layers first annealed at temperatures ≥725°C, coinciding with the observation of Si microcrystallites in the annealed layer prior to etching. The results suggest that an initial crystalline structure is important for fabricating luminescent PSLs.
Optoelectronic Characterizations of Porous Silicon
Authors: Koshida Nobuyoshi , Koyama Hideki
Published: March 2011

The optoelectronic properties of porous Si (PS) have been investigated in relation to the visible luminescence characteristics. First, the electronic structure has been characterized by spectroscopic ellipsometry and synchrotron orbital radiation (SOR) reflection spectra analyses. A retention of the original crystallinity, accompanied by a band gap widening, is confirmed by the optical reflection spectra and the optical constants behavior. Second, it is shown that there exists an intrinsic correlation between the visible photoluminescence characteristics of PS and its interfacial and electrical properties. These experimental results suggest that in the visible luminescence mechanism of PS, both band modification in Si crystallites and passivation at their surface play a complementary role to each other. The former ensures sufficient electronic excitation and the latter contribute to suppression of nonradiative relaxation.
Photoconductivity and Carrier Transport in Porous Silicon
Authors: Heben M. J. , Tsuo Y. S.
Published: March 2011

We present results from our investigations of the transport properties of p-type Si/porous silicon/Au devices. Current-voltage measurements were performed as a function of temperature from room temperature down to 23K and indicate that a tunneling mechanism governs the transport properties of these devices. Photocurrent spectroscopy measurements were performed as a function of temperature and excitation wavelength and support the conclusion that a tunneling mechanism is operative in these devices. The external quantum efficiencies of our porous-silicon-based structures can be greater than 20%, and the shape of the photocurrent spectra of porous-silicon-based devices, when compared to that of a p-type Si/Au diode, suggests that carriers photogenerated within porous silicon can be collected in an external circuit.
Mechanism of Electron Injection During the Anodic Oxidation of Silicon
Authors: Chazalvel J.-N. , Ozanam F.
Published: March 2011

n-Si photoanodes have been found to exhibit photocurrent multiplication during the first seconds of exposure to a fluoride-free, acidic electrolyte. This shows that, in contrast with earlier hypotheses, photocurrent doubling is not directly related to the presence of fluoride in the electrolyte, but rather must arise from an electron injection mechanism associated with the Si-H bonds initially present at the Si surface. It also suggests that the electroluminescence which has been observed during the anodic oxidation of porous silicon most probably stems from the same electron-injection mechanism.
Theory of Porous Silicon Injection Electroluminescence
Authors: Paul Maruska H. , Namavar F. , Kalkhoran N. M.
Published: March 2011

We discuss the operation of porous silicon light-emitting diodes prepared as heterojunctions between n-type In2O3:Sn (ITO) and p-type silicon nanostructures, exhibiting quantum confinement effects. The transparent ITO affords light emission through the top surface of the device, as well as providing passivation and hence long term stability. We describe a model for the injection of minority carrier electrons into the porous silicon regions, which results in the emission of yellow-orange DC electroluminescence. A detailed study of the forward bias current-voltage characteristics of the devices will be given, which allows calculations of the densities of interface states. A tendency to pin the hole fermi energy near the neutral level, φ0, is shown to control the extraction of majority carriers. Methods for improving LED efficiency by alleviating a parasitic shunt current path through interface states will be addressed.
Visible Electroluminescence from Pn Junction Type μc-Sic/ Porous Si / c-Si Structures
Authors: Futagi T. , Matsumoto T. , Katsuno M. , Ohta Y. , Mimura H. , Kitamura K.
Published: March 2011

We have fabricated two kinds of n-type microcrystalline silicon carbon (μc-SiC) / porous silicon (PS) / p-type crystalline silicon (c-Si) pn junctions and demonstrated a visible light emission from them. We have observed three types of visible light emission; an uniform red light emission at a forward current above 12mA/cm2 for the pn junction using a 0.2–0.4 Qcm c-Si substrate, and a very weak white light emission at a forward current of about 90 mA/mm2 and a strong orange-red light emission at a forward current from 200 to 619 mA/mm2for the pn junction using a 3.5–4.5 Ωcm c-Si substrate.
Role of Hydrogenated Surface in the Photoluminescence of Porous Silicon
Authors: Hirao Masahiko , Uda Tsuyoshi , Murayama Yoshimasa
Published: March 2011

Optical properties of hydrogenated silicon clusters are investigated by density functional pseudopotential calculation. Transitions between the band-edge orbitals are allowed, in contrast to the indirect gap in bulk silicon. The energy gaps of hydrogenated silicon particles of 15 to 30 Å in diameter are estimated to be 2.0 to 1.5 eV. When the cluster is dehydrogenated, localized states related to dangling bonds appear in the mid-gap, which decrease the photoluminescence intensity. These results agree with much experimental evidence and suggest that the photoluminescence of porous silicon is attributable to hydrogenated silicon particles.
Microcrystalline Silicon in a-SI:H Based Multljunction Solar Cells
Authors: Yang Liyou , Chen L. , Wiedeman S. , Catalano A.
Published: March 2011

Materials issues central to the application of microcrystalline silicon (μc-Si) doped layers in a-Si:H based solar cells are discussed, which include: (1) characterization of ultra-thin layers to be incorporated in the device, and (2) methods to promote nucleation of μc-Si on desired substrates within a thickness on the order of ∼100Å. Successful application of (μc-Si) in multijunction a-Si:H based solar cells are demonstrated.
Microcrystalline Silicon Prepared by VHF-GD: Structure, Transport and Optical Properties
Authors: Finger F. , Carius R. , Hapke P. , Prasad K. , Fliickiger R.
Published: March 2011

Doped and compensated microcrystalline silicon prepared by Very High Frequency Glow Discharge has been investigated by optical spectroscopy and by temperature dependence of the electrical conductivity. Raman spectroscopy confirms the microcrystalline nature of all samples with only small changes of the crystalline volume fraction upon doping. Strong absorption in the infrared region, which correlates with the conductivity, is attributed to free carrier absorption. As a function of temperature the conductivity of all samples shows a deviation from a purely activated behaviour. Consequences of this observation for transport mechanisms are discussed.
Conductance in Microcrystalline BbxCx/Si Heterojunction Diodes
Authors: Lee Sunwoo , Ton Thuong , Zych D. , Dowben P. A.
Published: March 2011

Plasma-enhanced chemical vapor deposited boron carbide (B1-xCx) thin films are shown to be a potential electronic material suitable for high temperature devices. The boron carbide films make excellent p-n heteroj unction diodes with /i-type silicon substrates. The B1-xCx/Si heteroj unction diodes are demonstrated to have rectifying properties at temperatures above 200°C and reverse current is strongly dependent on the energy of the band gap of the boron carbide films.
Microcrystalline Silicon by Dc Magnetron Sputtering: Growth Mechanisms
Authors: Feng G. F. , Katiyar M. , Yang Y. H. , Abelson J. R. , Maley N.
Published: March 2011

We have used real-time, in situ spectroscopie ellipsometry (SE) and infrared reflectance (IR) to study microcrystalline silicon (μc-Si) formation in reactive magnetron sputtering (RMS). μc-Si growth occurs at high hydrogen partial pressures and moderate substrate temperatures. We use IR studies and SE studies of film growth on rough surfaces, respectively, to show that these conditions lead to high hydrogen coverage of the film surface and high effective surface diffusivity. The interface region is amorphous and its thickness decreases with deposition rate. For a fixed growth flux, we observe a 30% decrease in the deposition rate of μc-Si relative to the amorphous interface region. This could be due to increased etching or decreased sticking coefficients during microcrystalline growth.
Hydrogen Configurations in Microcrystallized Sputtered Amorphous Silicon.
Authors: Lusson L. , Elkaim P. , Cuniot M. , Ballutaud D. , Rizk R. , Dixmier J.
Published: March 2011

Successive deuterium diffusion and effusion experiments are performed on undoped microcrystalline silicon obtained from thermally crystallized sputtered amorphous silicon thin films. The effect of prior incorporation of deuterium during the amorphous film growth on the crystallization mechanism and on the microcrystalline film quality is probed by the use of the post hydrogenation procedure. In connection with the deuterium solubility as provided by secondary ion mass spectroscopy (SIMS) profiling, the analysis of the effusion spectra suggests the existence of large cavities in the crystallized a-Si:D films, containing most probably molecular hydrogen. They are absent in the corresponding crystallized non-deuterated a-Si films. Other deuterium configurations seem to be present in both kinds of samples such as weakly bonded deuterium in small clusters and at grain boundaries.
Structure and Morphology of μic-SiC:H films Produced by PECVD
Authors: Demiehelis F. , Crovini G. , Pirri C. F. , Tresso E. , Battezzati L. , Rava P.
Published: March 2011

Films of μc-Si:H have been deposited in a conventional PECVD system in order to investigate their structural and morphological properties. They consist of a mixed phase of Si crystallites (50–200 Å), surrounded by grain boundaries, and amorphous regions. In this paper we report results obtained by different characterization techniques which have been used to deduce grain size, microcrystallinity fraction and composition of the crystalline, amoiphous and grain boundary. The amorphous matrix can be considered a covalent network where tetrahedrically coordinated carbon atoms, with 1 on 9 bonds terminated by hydrogen, exist. They form a distribution of large aromatic clusters containing a great number of aromatic rings such as to remarkably reduce the number of network terminators (hydrogen atoms).
Solute Binding at Void Surfaces in Silicon and germanium
Authors: Myers S. M. , Bishop D. M. , Follstaedt D. M. , Stein H. J. , Wampler W. R.
Published: March 2011

The strongly exothermic reactions of H and Cu with internal surfaces in Si and Ge were examined in experiments employing ion implantation, ion-beam analysis, transmission electron microscopy, and infrared spectroscopy. The dissociation energy of the Si-H surface bond was determined to be 2.6±0.1 eV, so that the monohydride is more stable than molecular H2, whose dissociation energy per atom is 2.26 eV. Initial experiments indicate a dissociation energy for the Ge-H surface bond of =1.9 eV. Copper is bound to the Si surface with an energy of 2.2±0.2 eV relative to solid solution, as compared to a reported binding energy of 1.5 eV for Cu in the precipitated Cu3Si phase.
Photoluminescence in B-doped μc-Si:H
Authors: Gu S. Q. , Viner J. M. , Taylor P. C. , Williams M. J. , Turner W. A. , Lucovsky G.
Published: March 2011

Photoluminescence (PL) has been investigated in hydrogenated microcrystalline silicon (μc-Si:H) samples as a function of boron doping for films prepared by remote plasma enhanced chemical vapor deposition. When the dark conductivity a is below about 10-5 S/cm, the PL spectra exhibit a shape which is close to that of the so-called band tail PL in undoped hydrogenated amorphous silicon (a-Si:H) at 77 K. When a increases, the PL intensity decreases at 77 K. For samples with a on the order of 10-3 S/cm, the PL spectra show only a narrow, low energy PL band which peaks around 0.8–0.9 eV. In these samples, the PL at higher energy is essentially not observable. This trend is similar to that which occurs in doped a-Si:H. However, for higher doping levels (σ ∼ 1 S/cm) the PL in μc-Si:H, although very weak, exhibits a broad band which contains intensity at higher energies. The absorption spectra in these samples, as measured by photothermal deflection spectroscopy (PDS), show the same relationships with the corresponding PL spectra as do the PDS spectra in doped a-Si:H.
Properties and Production Mechanism of Low-Temperature Deposited CAT-CVD Poly-Silicon films
Authors: Matsumura Hideki , Hosoda Yoichi , Furukawa Seijiro
Published: March 2011

Poly-silicon films are obtained at temperatures as low as 400 °C by the catalytic chemical vapor deposition (cat-CVD) method, in which deposition gases are decomposed by the catalytic or pyrolytic reactions with a heated catalyzer near substrates. It is found that there are roughly two modes of deposition conditions such as low gas pressure mode and high gas pressure mode for obtaining poly-silicon films, and also that the Hall mobility of the cat-CVD poly-silicon films of low gas pressure mode sometimes exceeds over 100 cm2/Vs.
Photoluminescence from Microcrystalline Silicon and Related Materials
Authors: Rlickschloss M. , Landkammer B. , Ambacher O. , Vepřek S.
Published: March 2011

Intense photoluminescence has been obtained from nanocrystal-line silicon prepared in completely dry processing by the optimizing the crystallite size and the chemical passivation of the grain boundaries due to a controlled postoxidation of the plasma deposited films.
Excimer Lasbr Induced Crystallization of thin Amorphous Si Films on SiO2: Implications of Crystallized Microstructures for Phase Transformation Mechanisms
Authors: Kim H. J. , Im James S. , Thompson Michael O.
Published: March 2011

Using planar view transmission electron microscope (TEM) and transient reflectance (TR) analyses, we have investigated the excimer laser crystallization of amorphous silicon (a-Si) films on SiO2. Emphasis was placed on characterizing the microstructures of the single-shot irradiated materials, as a function of the energy density of the laser pulse and the temperature of the substrate. The dependence of the grain size and melt duration as a function of energy density revealed two major crystallization regimes. In the low energy density regime, the average grain size first increases gradually with increases in the laser energy density. In the high energy density regime, on the other hand, a very fine grained microstructure, which is relatively insensitive to variations in the laser energy density, is obtained. In addition, we have discovered that at the transition between these two regimes an extremely small experimental window exists, within which an exceedingly large grain-sized polycrystalline film is obtained. We suggest a liquid phase growth model for this phenomenon, which is based on the regrowth of crystals from the residual solid islands at the oxide interface.
Large-Grain Doped Poly-Si Films Fabricated Using New Excimer Laser Annealing Technique
Authors: Iwata Hiroshi , Nohda Tomoyuki , Ishida Satoshi , Kuwahara Takashi , Sano Keiichi , Kuriyama Hiroyuki , Noguchi Shigeru , Hanafusa Hiroshi , Kiyama Keiichi , Tsuda Shinya , Nakano Shoichi , Kuwano Yukinori
Published: March 2011

The grain size of phosphorous (P)-doped poly-Si film has been enlarged to about 5000 Å by controlling the solidification velocity of molten Si during ArF excimer laser annealing. The drastically enlarged grain has few defects inside the grain. It has been confirmed that control of the solidification velocity is effective for P-doped poly-Si similar to the case of non-doped poly-Si films. In addition, a sheet resistance of 80 Ω/□ (ρ = 4 × 10-4 Ω · cm) has been achieved for very thin (500 Å) films by recrystallizing PECVD P-doped a-Si films.
Nanocrystallites of Si Embedded in CaF2 by Molecular Beamepitaxy (MBE)
Authors: Taylor A. P. , Stokes K. , Wu Z. C. , Persans P. D. , Schowalter L. J. , LeGoues F. K.
Published: March 2011

Thin films of CaF2 containing layers of Si nanocrystals were grown epitaxially on Si(111) substrates by MBE. When Si is deposited epitaxially on CaF2 it forms islands and, by choosing appropriate growth conditions, a composite of Si nanocrystals embedded in a CaF2 host crystal is obtained which we have observed with TEM. We varied the effective Si concentration in the composite region from 1% to 25%. The CaF2 could be grown with high crystal quality as demonstrated by ion channeling results which gave Ca xmin's as low as 4.7%. Raman spectra of the CaF2 containing Si nanocrystallites showed significant shifts toward lower energies. EUipsometry measurements were performed on a number of samples over a range of effective Si concentrations and Maxwell-Garnett effective medium theory was used to fit the data. A key technological advantage to this approach is that the epitaxial Si/CaF2 composite material is readily integrable into VLSI processing.
Si-Cluster Luminescence
Authors: Saunders Winston A. , Atwater Harry A. , Vahala Kerry J. , Flagan Richard C. , Sercel Peter C.
Published: March 2011

We report on a technique for generating Si-clusters in the nanometersize regime. The cluster source is capable of generating micron-thick cluster films in a few minutes. The cluster films luminesce in thevisible and infrared. Source construction is discussed. Electron micrographs of the clusters are shown. Luminescence and optical absorption spectra for the clusters are presented.
Optical Properties of InGaAs/InP Quantum Wires Defined by High Voltage Electron Beam Lithography at 200 kV
Authors: Ils P. , Michel M. , Forchel A. , Gyuro I. , Speier P. , Zielinski E.
Published: March 2011

We have fabricated and analyzed high quality InGaAs/InP quantum wires by electron beam lithography and wet chemical etching. In order to optimize the shape of the wet-etched wires different wire orientations were investigated. As results of the lithography process we obtain wire masks with widths down to 15 nm and etched wires with widths of the InGaAs layer of 18 nm.

The wires were studied optically by means of photoluminescence spectroscopy. In contrast to dry etched wire structures the wet chemically etched wires show strong optical emission even for geometrical widths less than 25 nm. The weak decrease of the quantum efficiency with decreasing wire width indicates that there are no dead layers at the side walls of the wires, which is in contrast to previous studies on dry-etched structures. The photoluminescence energy of the InGaAs/InP wires is independent of the wire dimension down to widths of 50 nm. This indicates that a steep lateral potential in our structures is obtained due to the confinement by the semiconductor/vacuum transition at the etched surfaces. For wires with smaller widths an increasing blue shift of photoluminescence energy up to more than 30 meV is observed.
Studies of Quantum Dots Fabricated by Combining Aerosol and Plasma Etching Techiques
Authors: Samuelson Lars , Maximov Ivan , Gustafsson Anders , Liu Xiao , Seifert Werner , Hansson Hans-Christen , Wiedensohler Alfred
Published: March 2011

A new approach has been taken for the fabrication of Quantum Dot materials to be used for physics as well as for opto-electronics applications. We used a generation technique of ultrafine aerosol Ag particles which are deposited onto the surface of GalnAs/InP quantum well structures grown by Metal Organic Vapor Phase Epitaxy (MOVPE). The particles, ranging in size between 30 and 40 nm, are subsequently used as an etching mask. The Ag aerosol produced by homogeneous nucleation and can have a mean diameter in the range 2 – 100 nm. After size-selection, monodisperse particles with a very narrow size distribution are deposited onto the semiconductor surface at a density of about 109 cm-2. Low energy CH4/H/Ar Electron Cyclotron Resonance (ECR) plasma etching results in the formation of free-standing InP columns 50 to 80 nm in diameter and 120 to 280 nm in height. Their size and stability were found to be dependent on the etching conditions and the diameter of the particles. Low-temperature cathodoluminescence (CL) was used to evaluate the quantum dot structures fabricated by this technique.
Optical Properties of Metal Coated Particles
Authors: Haus Joseph W. , Zhou H. S. , Honma I. , Komiyama H.
Published: March 2011

Metal-coated particles of nanometer dimensions can exhibit unusual optical properties due to the local-field enhancement mechanism. However, the properties are affected by uncontrollable factors that degrade the expected performance. In this paper we report theoretical results of coating thickness variations and diffuse interface effects on the optical absorption and the nonlinear optical response of particles with a CdS core and a silver coating. The linear and nonlinear optical properties are discussed within the context of the effective medium theory for small volume fractions.
Piezoresistivity of Polycrystalline Diamond Films
Authors: Wur Der-Rern , Davidson Jim L.
Published: March 2011

Polycrystalline diamond film (PDF) is known for its high power, high temperature, and radiation hard potential. The interest in piezoresistivity of PDF is that it is a candidate for high temperature sensing (e.g., pressure sensor).

Piezoresistivity measurements were taken of boron-doped PDF grown by microwave-plasma chemical vapor deposition(CVD). Three substrates, silicon, aluminum nitride and tungsten were used. Films were detached from these substrates, then attached to a ceramic substrate. The piezoresistivity varies, dependent on the original host substrate. For example, at room temperature, the PDF film from tungsten has a greater gauge factor, around 75. The carrier activation energy of this film, determined from log R(l/T), was nominally 0.25eV.

Combining thick film technology and CVD processes, patterned B-doped PDF has been achieved monolithically on A1N substrates. The characteristics of this configuration is being investigated and will be presented.
Electrical and Optical Properties of Indium Doped Zinc Oxide Films Prepared by Atmospheric Pressure Chemical Vapor Deposition
Authors: Hu Jianhua , Gordon Roy G.
Published: March 2011

Indium doped zinc oxide films have been deposited from diethyl zinc, ethanol and trimethyl indium in the temperature range between 225°C and 450°C in a laminar flow atmospheric chemical vapor deposition reactor. Both doped and undoped films were crystalline. The doped films have electron density up to 9×1020 cm-3, conductivity up to 850 Ω-1cm-1, and mobility up to 8 cm2/Vs. The indium doping increases the average visible absorption from less than 1% to above 20%. The transparency and conductivity of indium doped zinc oxide films are lower than those of fluorine doped films.
Study of Solar Cells by Sem Dark Voltage Contrast
Authors: Mil'Shtein S. , Iatrolt S. , Kharas D. , Bell R. O. , Sandstrom D.
Published: March 2011

For the first time the Scanning Electron Microscopy (SEM) Dark Voltage Contrast (DVC) technique was used to examine the field distribution in a solar cell made of polycrystalline silicon.

The samples were cut off solar cells made of Edge-defined Film-fed Grown (EFG) Silicon and lapped at 2 and 5 degree angles. The DVC measurements were performed at forward, reverse, and zero bias conditions using a Hitachi S-570 SEM and a Kevex-8000 microanalyzer.

The I-V curves were recorded to test the electric performance of the samples. We examined two groups of solar cells. One group of cells demonstrated, after regular processing, reasonable electrical performance and abrupt DVC profile. The other group was intentionally doped with titanium, which presumably was agglomerated in the p-n junction area thus degrading completely the electrical performance of the cells and weakening the electric field by a factor of 4–6.
Characterization of Porous Silicon: Structural, Optical and Electrical Properties
Authors: Badoz P. A. , Bensahel D. , Bomchil G. , Ferrieu F. , Halimaoui A. , Perret P. , Regolini J. L. , Sagnes I. , Vincent G.
Published: March 2011

The aim of this paper is to provide a better understanding of photoluminescent porous silicon (PS) microstructure in relation to their electronic properties: absorption band edge shift1 and quantum confinement hypothesis1,2, dielectric constant evolution and electroluminescence characteristics.

Results concerning the p type PS microstructure characterization by X ray diffraction and electron microscopy are presented showing a noticeable decrease in crystallite size and surface area with decreasing substrate doping and increasing porosity.

The optical transmission of homogeneous free-standing PS layers of different porosities and substrate dopings is studied, showing no evidence of a direct energy gap in PS. On the contrary, a large blue shift of the optical absorption edge, taking into account the total Si mass content in the PS film, is demonstrated. This shift is well correlated with the crystallite size variations with porosity and substrate doping and is attributed to a quantum confinement of electronic wavefunctions in the nanocrystallites.

On the other hand, ellipsometry measurements show the PS absorption to be little affected by the microcrystalline structure of the material in the 3.5–5 eV range, i.e. above the direct band gap of bulk Si. This indicates that, if confirmed, the quantum confinement strongly affects the PS joint density of states in the vicinity of the Si band edge and, as could be expected, to a much lesser degree near the edge of the confining potential.

Capacitance voltage measurements of thin PS layers allow the determination of the dielectric constant which is shown to decrease with increasing porosity. This behavior is in reasonable agreement with theε values deduced from the transmission experiments in the near infrared. Furthermore, it is shown that this dependence on porosity is well accounted for by the Bruggeman effective medium approximation.

Finally, recent results concerning visible light emission from solidstate porous silicon devices will be presented: I-V characteristics, electroluminescence intensity and dynamic, quantum efficiency and device ageing.
On the Contribution of a Nitrogen-Related Defect in the Nexafs Spectra of Thin Si3N4Films
Authors: Paloura E. C. , Knop A. , Dobler U. , Holldack K. , Logothetidis S.
Published: March 2011

Thin amorphous SiN films grown on Si are studied with Near Edge X-Ray Absorption Fine Structure (NEXAFS). The NEXAFS spectra of N-rich films are characterized by a strong resonance line (RL) at the onset of the N K- edge. The intensity of the RL in N-rich films increases with the N/Si ratio, while the same RL is detected in the NEXAFS spectra of stoichiometric SiN films subjected to damage with Ar+ion bombardment. The RL is attributed to a N-related defect which is strongly localized in a pure 2p orbital. The RL, which is identified as a bulk nitride property, can be annealed out at temperatures higher than the growth temperature. It is proposed that the annealing process of the RL, which is characterized by an activation energy of 0.87eV, is due to Si-N bond formation, where the Si atoms are provided by the stressed SiN/Si interface.
Anomalous Behavior of Semi-Insulating Silicon Rich Amorphous Silicon Nitride
Authors: Bernstein J. B. , Gleason E. F. , Wetsel A. E. , Liu E. Z. , Wyatt P. W.
Published: March 2011

Silicon rich PECVD amorphous silicon nitride has been used as an inter-level metal dielectric for making laser programmable connections on restructurable VLSI. There is an apparent Schottky barrier characteristic that has a 0.11 eV lower barrier for Ti than for Al. The stoichiometry was analyzed using RBS and HFS, and found to contain approximately 55% Si, 25% N, and 20% H by atomic percentages. The optical bandgap is 2.01 eV as found by the Tauc method.

The insulating behavior depends on time in an anomalous manner at applied fields greater than about 0.2 MV/cm, whereby the current increases with time for several secondsuntil it reaches an equilibrium value. The current decays in a normal charging manner at lower fields and in samples with insulating sub-layers between the electrodes and thenitride. When used as a gate dielectric, there is a long-time charging behavior that shifts the flat band voltage in the opposite direction of the applied stress. This shift is indicative of polarization within the dielectric. This behavior is similar to that of a reverse biased a-Si:H p-i-n diode.
Thermal Properties of Thin Films
Authors: Lambropoulos J. C. , Hwang S.-S.
Published: March 2011

We summarize various measurements of the thermal conductivity of thin ceramic films which show that the thermal conductivity of thin films with thickness in the micron and sub-micron range may be up to two orders of magnitude lower than the thermal conductivityof the corresponding bulk solid. The reduction in the thin film effective thermal conductivity is attributed to the interfacial thermal resistance across the film/substrate interface.
Floating Temperature Deposition of Device Quality SiO2 Thin Films by DECR Plasma
Authors: Agius B. , Hugon M. C. , Jiang N. , Varniere F. , Plais F. , Pribat D. , Froment M. , Puech M.
Published: March 2011

Low temperature deposition of dielectric thin films is more and more used in very largescale integrated (VLSI) circuits. For this purpose, distributed electron cyclotron resonance (DECR) plasma appears to be a promising tool. The most interesting feature of this recent plasma is the high ion density (≈1011 cm−3) associated with low electronic temperature (2–3eV) and low energy species (20–30 eV). The purpose of this study is to discuss the effects of the reactant gas mixture composition (O2sol;SiH4) and the rf substrate bias power on the physical, chemical and electrical properties of DECR SiO2 films deposited at floating temperature (<100°C). Under optimum deposition conditions, the films show excellent characteristics, comparable to those obtained with thermal oxides grown at 850–1050°C.
Impact Ionization, Degradation, and Breakdown in SiO2
Authors: Dimaria D. J. , Cartier E. , Arnold D.
Published: March 2011

Destructive breakdown in silicon dioxide is shown to be strongly correlated to the oxide degradation caused by hot-electron-induced defect production and charge trapping ner the interfaces of the films. Two well defined transitions in the chargc-to-breakdown data as a function of field and oxide thickness are shown to coincide with the onset of mechanisms due to trap creation and impact ionization by electrons with energies exceeding 2 and 9 eV (the SiO2 bandgap energy), respectively. The temperature dependence of charge-to-breakdown is also shown to be consistent with that of these two defect-producing mechanisms.
Injection-Related Damage in Metal-Oxide-Silicon Tunnel Diodes
Authors: Farmer K. R. , Lundgren P. , Andersson M. O. , Engstrom O.
Published: March 2011

Current-voltage and conductance-voltage characterization is used to study high bias related “positive charge” in MOS tunnel diodes fabricated on p-type substrates. This charge effect appears to be associated with interface state levels that are located both throughout the band gap, and at a well-defined energy level roughly 0.3 eV above the silicon valence band edge. The well-defined state apparently acts as a tunnelingcenter communicating with the gate electrode and the silicon valence band. In addition, the first observation of high bias related charge is reported for tunnel diodes built on n-type substrates. This charge has positive character at low bias levels, transforming to net negative charge at high gate voltages.
Measurement of High Voltage Stress Induced Traps Inside Thin Silicon Oxide Films
Authors: Dumin D. J. , Maddux J. R.
Published: March 2011

After thin silicon oxide films were stressed at high voltages, two changes occurred in the current-voltage and transient current characteristics of the films. The low-level, pre-tunneling current rose and the transient decay of the current after removal of a voltage pulse changed from an exponential RC time constant decay to a very long decay that was characterized by a 1/t time dependence. Using an extension of the tunneling front discharge model, previously developed to describe the transient changes in the threshold voltages of transistors after avalanche injection or irradiation, the 1/t time dependence was derived. This 1/t transient discharge current was used to determine the density and distribution of the traps inside of the oxide after the high voltage stress. The technique and model used for determining the trap densities and distributions from the transient currents will be described. The model was used to describe the charging of traps in the oxide.
Detection of Hydrogen in Bulk and Thin Film Silicon Dioxide by Hydrogen Nuclear Magnetic Resonance
Authors: Levy D. H. , Gleason K. K.
Published: March 2011

Hydrogen is a common impurity in silicon dioxide (SiO2) which can influence its optical and electronic properites. Here, nuclear magnetic resonance (NMR) is applied to study of hydrogen in these materials, despite their relatively low hydrogen content. We present results for bulk fused silica as well as thermally grown films of SiO2 on silicon. These experiments demonstrate the potential of solid state NMR for studying low hydrogen content film systems. In bulk fused silica, we have observed that although the majority of hydrogen is isolated, a small number of centers exist involving adjacent silanol pairs. These pairs react during high temperature annealing as well as during deep ultraviolet irradiation. Furthermore, the presence of these centers is related to the susceptibility of fused silica to radiation damage. The results obtained on the fused silica material are compared to SiO2 films on silicon. The NMR spectra and relaxation associated with thick (>1μm) wet SiO2 films are similar to those for the fused silica while the NMR data for thinner oxide more closely resembles those of surface water on silica gel.
Depth Profiling of Oxygen Vacancy Defect Generation in Buried SiO2
Authors: Stesmans A. , Vanheusden K.
Published: March 2011

Oxygen-vacancy defects (E') generated at the surface of buried SiO2 layers formed by O+ implantation during the separation by implantation of oxygen (SIMOX) process have been studied by electron spin resonance (ESR) at 4.2 K. The E' damage was generated during exposure to a dc Ar glow discharge that produces defects predominantly in a surface layer of ≈100 Å thick, reaching local volume densities at the surface up to 8 × 1019 cm−3. This glow discharge exposure, alternated with step-by-step etch back, allowed mapping of a defect generation sensitivity depth profile of the buried oxide (BOX) layer, revealing a fairly uniform sensitivity with a strong decline towards the BOX/substrate interface. Besides the usual E' γ signal, the E'δj center — a delocalized variant of the E' center — has been newly observed in the BOX. Reoxidation of the BOX was observed to reduce the E' sensitivity close to that of regular dry thermal oxide (≥ 29 times lower), while the E'γ signal could no longer be generated, again similar to conventional thermal oxide. These data suggest a revision of the model for the E' defect. In general, the results strongly suggest that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.
Quasi-Stoichiometric Silicon Nitride Thin Films Deposited by Remote Plasma-Enhanced Chemical-Vapor Deposition
Authors: Lucovsky G. , Ma Y. , He S. S. , Yasuda T. , Stephens D. J. , Habermehl S.
Published: March 2011

Conditions for depositing quasi-stoichiometric silicon nitride films by low-temperature, remote plasma-enhanced chemical-vapor deposition, RPECVD, have been identified using on-line Auger electron spectroscopy, AES, and off-line optical and infrared, IR, spectroscopies. Quasi-stoichiometric films, by the definition propose in this paper, do not display spectroscopic evidence for Si-Si bonds, but contain bonded-H in Si-H and Si-NH arrangements. Incorporation of RPECVD nitrides into transistor devices has demonstrated that electrical performance is optimized when the films are quasi-stoichiometric with relatively low Si-NH concentrations.