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Applied Surface Science (v.256, #18)
International conference: Progress in Applied Surface, Interface, and Thin Film Science – Solar Renewable Energy News II (SURFINT – SREN II), Florence, November 15–20, 2009, Italy
by Emil Pincik (pp. 5591-5591).
Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching by A. Boukezzata; A. Keffous; A. Cheriet; Y. Belkacem; N. Gabouze; A. Manseri; G. Nezzal; M. Kechouane; A. Bright; L. Guerbous; H. Menari (pp. 5592-5595).
In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K2S2O8 solution under UV illumination at 254nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6MΩcm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K2S2O8 solution has been proposed.
Keywords: PACS; 71.23.Cq; 81.20.−n; 78.60.−b; 78.66.−wSilicon carbide; Thin layer; Photochemical etching; SIMS; SEM
On photoluminescence properties of a-Si:H-based structures by R. Brunner; E. Pinčík; H. Kobayashi; M. Kučera; M. Takahashi; J. Rusnák (pp. 5596-5601).
Non-Gaussian photoluminescence peaks observed in a-Si:H-based structures at 6K are interpreted as a consequence of the presence of different phases in material. Thin films of amorphous silicon deposited on glass substrate have been analyzed.The main aims of the contribution are (i) analysis of numerical data obtained by fitting procedure and (ii) formulation of corresponding conclusions in terms of structural properties of sample. Spectrum of a-Si:H-based samples can be interpreted as superposition of photoluminescence signals arising from two domains with different degrees of structural disordering. By our knowledge this result corresponds to real situation from view of structural properties of amorphous hydrogenated silicon. Under certain circumstances, decomposition of photoluminescence spectrum can give information of geometrical structure of sample.
Keywords: PACS; 78.55.−m; 78.55.Qr; 81.05.GcAmorphous silicon; Photoluminescence; Nanoclusters
Fabrication of diamond nanorods for gas sensing applications by Marina Davydova; Alexander Kromka; Bohuslav Rezek; Oleg Babchenko; Martin Stuchlik; Karel Hruska (pp. 5602-5605).
Diamond nanorods were fabricated for a sensing device by utilizing reactive ion etching in CF4/O2 radio frequency plasma. The length of the nanorods has been controlled by the ion etching time. The obtained morphologies were investigated by scanning electron microscopy. The gas sensing properties of the H-terminated diamond-based sensor structures are indicating that we have achieved high sensitivity to detect phosgene gas. Also, our sensor exhibited good selectivity between humid air and phosgene gas if the measurement is conducted at elevated temperatures, such as 140°C. Furthermore, such sensor response rating could reach as high value as 4344 for the phosgene gas, which was evaluated for the sample consisting of the longest nanorods (up to 200nm).
Keywords: PACS; 73.63.Bd; 61.46.Km; 81.05.ug; 81.15.Gh; 68.55.ANanocrystalline diamond; Diamond nanorods; Surface conductivity; Gas sensor; SEM
Surface modification of doped ZnO thin films by S. Flickyngerova; J. Skriniarova; M. Netrvalova; J. Kovac Jr.; I. Novotny; P. Sutta; V. Tvarozek (pp. 5606-5609).
Effects of photo-assisted electrodeless and ion RF-sputter etching on the structural and optical properties of sputtered ZnO:Al thin films were investigated. Photo-assisted electrodeless etching was appropriate for getting “smooth” surfaces and ion RF-sputter etching by high power has significantly modified the surface roughness with an increase of the light diffuse transmittance.
Keywords: PACS; 68.55 jm; 68.37.Ps; 78.66.Hf; 81.15.CdThin-film solar cell; ZnO:Al; Sputtering
Low temperature fabrication of 5–10nm SiO2/Si structure using advanced nitric acid oxidation of silicon (NAOS) method by Yousuke Fukaya; Takashi Yanase; Yasushi Kubota; Shigeki Imai; Taketoshi Matsumoto; Hikaru Kobayashi (pp. 5610-5613).
We have developed the advanced nitric acid oxidation of Si (NAOS) method to form relatively thick (5–10nm) SiO2/Si structure with good electrical characteristics. This method simply involves immersion of Si in 68wt% nitric acid aqueous solutions at 120°C with polysilazane films. Fourier transform infrared absorption (FT-IR) measurements show that the atomic density of the NAOS SiO2 layer is considerably high even without post-oxidation anneal (POA), i.e., 2.28×1022 atoms/cm2, and it increases by POA at 400°C in wet-oxygen (2.32×1022 atoms/cm2) or dry-oxygen (2.30×1022 atoms/cm2). The leakage current density is considerably low (e.g., 10−5A/cm2 at 8MV/cm) and it is greatly decreased (10−8A/cm2 at 8MV/cm) by POA at 400°C in wet-oxygen. POA in wet-oxygen increases the atomic density of the SiO2 layer, and decreases the density of oxide fixed positive charges.
Keywords: PACS; 81.60.Cp; 73.40.Qv; 85.40.Hp; 73.61.NgLow temperature oxidation; Nitric acid oxidation; Silicon; MOS; Silicon dioxide
Electrical behaviour of lateral Al/n-GaN/Al structures by Zs. J. Horváth; L. Dobos; B. Beaumont; Z. Bougrioua; B. Pécz (pp. 5614-5617).
The electrical behaviour of lateral Al/n-GaN/Al structures has been studied by current–voltage measurements between a large pad with an area of 22mm2 and small contacts with different areas in the range of 0.01–1mm2. The results indicated that near room temperature the current was limited by the GaN layer exhibiting linear I– V characteristics for large contacts around 1mm2, while it was contact limited for small contacts around 0.1mm2 and below. This indicates that the same metal contact can behave as ohmic or rectifying depending on the contact area and so on the ratio of contact resistance to the series resistance of the structure.Near liquid nitrogen temperature, the current through the lateral Al/n-GaN/Al structures was limited by space charges. The Al/n-GaN contacts exhibited a very low Schottky barrier height below or around 0.2eV. A new possible mechanism responsible for the temperature dependence of the ideality factor is proposed.
Keywords: PACS; 7330; 7340GGaN; Ohmic contact; Low Schottky barrier; Current–voltage characteristics; Space charge limited current
Preparation and structural properties of YBCO films grown on GaN/ c-sapphire hexagonal substrate by Š. Chromik; P. Gierlowski; M. Španková; E. Dobročka; I. Vávra; V. Štrbík; T. Lalinský; M. Sojková; J. Liday; P. Vogrinčič; J.P. Espinos (pp. 5618-5622).
Epitaxial YBCO thin films have been grown on hexagonal GaN/ c-sapphire substrates using DC magnetron sputtering and pulsed laser deposition. An MgO buffer layer has been inserted between the substrate and the YBCO film as a diffusion barrier. X-ray diffraction analysis indicates a c-axis oriented growth of the YBCO films. Φ-scan shows surprisingly twelve maxima. Transmission electron microscopy analyses confirm an epitaxial growth of the YBCO blocks with a superposition of three a– b YBCO planes rotated by 120° to each other. Auger electron spectroscopy and X-ray photoelectron spectroscopy reveal no surface contamination with Ga even if a maximum substrate temperature of 700°C is applied.
Keywords: PACS; 74.72h; 73.61EyMagnetron sputtering; Pulsed laser deposition (PLD); YBCO thin films; GaN substrates; X-ray diffraction; Transmission electron microscopy; Auger electron spectroscopy
On the influence of the surface roughness onto the ultrathin SiO2/Si structure properties by Stanislav Jurečka; Hikaru Kobayashi; Masao Takahashi; Taketoshi Matsumoto; Mária Jurečková; Ferdinand Chovanec; Emil Pinčík (pp. 5623-5628).
The surface roughness of the semiconductor substrate substantially influences properties of the whole semiconductor/oxide structure. SiO2/Si structures were prepared by using low temperature nitric acid oxidation of silicon (NAOS) method and then the whole structure was passivated by the cyanidization procedure. The influence of the surface morphology of the silicon substrate onto the electrical properties of ultrathin NAOS SiO2 layer was investigated. Surface height function properties were studied by the AFM method and electrical properties were studied by the STM method. The complexity of analyzed surface structure was sensitive to the oxidation and passivation steps. For describing changes in the oxide layer structure, several fractal measures in an analysis of the STM images were used. This fractal geometry approach enables quantifying the fine spatial changes in the tunneling current spectra.
Keywords: PACS; 68.35.bg; 68.35.Ct; 68.37.Ef; 68.37.PsSemiconductor; Thin film; Surface roughness; Fractal methods; Atomic force microscopy (AFM); Scanning tunneling microscopy (STM)
Investigation of porous silicon carbide as a new material for environmental and optoelectronic applications by A. Keffous; N. Gabouze; A. Cheriet; Y. Belkacem; A. Boukezzata (pp. 5629-5639).
In this paper, we present an experimental study on the chemical and electrochemical etching of silicon carbide (SiC) in different HF-based solutions and its application in different fields, such as optoelectronics (photodiode) and environment (gas sensors). The thin SiC films have been grown by pulsed laser deposition method. Different oxidant reagents have been explored. It has been shown that the morphology of the surface evolves with the etching conditions (oxidant, concentration, temperature, etc.). A new chemical polishing solution of polycrystalline 6H-SiC based on HF:Na2O2 solution has been developed. Moreover, an electrochemical etching method has been carried out to form a porous SiC layer on both polycrystalline and thin SiC films. The PL results show that the porous polycrystalline 6H-SiC and porous thin SiC films exhibited an intense blue luminescence and a green-blue luminescence centred at 2.82eV (430nm) and 2.20eV (560nm), respectively. Different device structures based on both prepared samples have been investigated as photodiode and gas sensors.
Keywords: PACS; 71.20.Nr; 78.20.−e; 78.40.−q; 78.55.−mSilicon carbide; Electro(chemical); PSC; Gas sensing; Photodiode
Rough surface scattering simulations using graphics cards by Petr Klapetek; Miroslav Valtr; Aleš Poruba; David Nečas; Miloslav Ohlídal (pp. 5640-5643).
In this article we present results of rough surface scattering calculations using a graphical processing unit implementation of the Finite Difference in Time Domain algorithm. Numerical results are compared to real measurements and computational performance is compared to computer processor implementation of the same algorithm. As a basis for computations, atomic force microscope measurements of surface morphology are used. It is shown that the graphical processing unit capabilities can be used to speedup presented computationally demanding algorithms without loss of precision.
Keywords: PACS; 42.25.Fx; 78.68.+mFDTD; Graphical processing unit
Wet sulfur passivation of GaSb(100) surface for optoelectronic applications by E.V. Kunitsyna; T.V. L’vova; M.S. Dunaevskii; Ya.V. Terent’ev; A.N. Semenov; V.A. Solov’ev; B.Ya. Meltser; S.V. Ivanov; Yu.P. Yakovlev (pp. 5644-5649).
A comparative analysis of the properties of the non-passivated and S-passivated GaSb(100) surfaces has been performed through PL, AFM and RHEED characterization. The samples treated with a 1M Na2S aqueous solution demonstrate an increase in the 5K PL intensity. According to AFM data, the annealing of the S-passivated GaSb(100) leads to the formation of the clean flat (100) surface. Moreover, after annealing the PL intensity of the S-passivated GaSb(100) surfaces decreases by 20%, whereas for the non-passivated samples it drops by more than a factor of 4. The method of wet sulfur passivation has shown great effectiveness in pre-epitaxial processing for LPE and MBE growth of the GaSb-related materials for optoelectronics.
Keywords: PACS; 81.05.Ea; 81.65.Rv; 81.65.Cf; 78.55.Cr; 68.37.Ps; 73.40.KpGaSb; Passivation; Annealing; Photoluminescence; AFM; LPE; MBE
Study of structural and optical properties of ZnO films grown by pulsed laser deposition by S. Lemlikchi; S. Abdelli-Messaci; S. Lafane; T. Kerdja; A. Guittoum; M. Saad (pp. 5650-5655).
Wurtzite zinc oxides films (ZnO) were deposited on silicon (001) and corning glass substrates using the pulsed laser deposition technique. The laser fluence, target–substrate distance, substrate temperature of 300°C were fixed while varying oxygen pressures from 2 to 500Pa were used. It is observed that the structural properties of ZnO films depend strongly on the oxygen pressure and the substrate nature. The film crystallinity improves with decreasing oxygen pressure. At high oxygen pressure, the films are randomly oriented, whereas, at low oxygen pressures they are well oriented along [001] axis for Si substrates and along [103] axis for glass substrates. A honeycomb structure is obtained at low oxygen pressures, whereas microcrystalline structures were obtained at high oxygen pressures. The effect of oxygen pressure on film transparency, band gap E g and Urbach energies was investigated.
Keywords: PACS; 81.15.Fg; 78.55.Et; 68.55.J; 61.05.cp; 68.55.jmPLD; ZnO; DRX; Morphology; Texture coefficient
The roughness surface expressed by the mathematical model by Anna Macurova (pp. 5656-5658).
The work investigates the effect of some characteristics of a cut surface and studies roughness of the cutting process. There is elaborated theoretical information and new aspects on calculation of the theoretical values of the roughness of the cut surface for the chosen materials are formulated. In the area of the experimental investigation, results on characteristics of the chosen materials are formulated in this work. Obtained results are fundamental for the mathematical modulation and mathematical analysis for the investigated dependencies for the cut surfaces. The mathematical model also represents the specific dependencies of the technological process. The characteristics of the observed parameters are approximated by characteristics of the quasi-linear models. The solution of this model offers acceptable results. The mathematical models of the roughness of the cut surface are a mathematical description of the dependency of the maximum roughness of the cut surface of the feed represented by the differential equation and by the integral curves.
Keywords: PACS; 02.30 Hq; 87.80EkRoughness; Surface; Differential equation
Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy by D. Hernández-Maldonado; M. Herrera; D.L. Sales; P. Alonso-González; Y. González; L. González; J. Pizarro; P.L. Galindo; S.I. Molina (pp. 5659-5661).
The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.
Keywords: PACS; 68.37.Lp; 81.05.Ea; 81.15.HiQuantum dots molecules; Droplet epitaxy; Transmission electron microscopy; Semiconductors
Influence of the broken symmetry of defect state distribution at the a-Si:H/c-Si interface on the performance of hetero-junction solar cells by Miroslav Mikolášek; Juraj Racko; Ladislav Harmatha; Pavol Gašpierik; Pavol Šutta (pp. 5662-5666).
Taking into account the fact that the distribution of defect states at the interface does not have strictly symmetrical shape, we present a simulation study of a-Si:H(n)/c-Si(p) and a-Si:H(p)/c-Si(n) structures with regard to the defect states at the interface, band offsets and doping concentration of the emitter. The presented results suggest for a-Si:H(n)/c-Si(p) solar cells a strong influence of the introduced broken symmetry between acceptor and donor defect states on the open-circuit voltage, whereas the a-Si:H(p)/c-Si(n) structure benefits from inherent favorable band alignment and remains unaffected.
Keywords: PACS; 85.30.De; 85.60.BtBroken symmetry; Defect states at the interface; a-Si:H/c-Si hetero-junction; Solar cell
A study of optical absorption in amorphous hydrogenated silicon thin films of varied thickness by J. Müllerová; L. Prušáková; M. Netrvalová; V. Vavruňková; P. Šutta (pp. 5667-5671).
We report results obtained from optical absorption studies carried out on amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane plasma. The influence of the film thickness was studied on the two series of samples deposited from undiluted silane and under moderate hydrogen dilution of silane. Spectral refractive indices and absorption coefficients were determined from transmittance spectra. The spectral absorption coefficients were used to determine the Tauc optical band-gap energies Eg, the B factors of the Tauc plots, the iso-energy values E04 (energy at which the absorption coefficient is equal to 104cm−1). The results were correlated with volume fractions of the amorphous phase and voids and with the film thickness.
Keywords: PACS; 78.66.Jg; 68.55.−a; 78.30.−j; 81.40.−zThin-film silicon; Hydrogenated amorphous silicon; Thickness; Absorption coefficient; Optical band-gap energy
Dependence of Curie temperature on surface strain in InMnAs epitaxial structures by J. Novák; I. Vávra; Z. Križanová; S. Hasenöhrl; J. Šoltýs; M. Reiffers; P. Štrichovanec (pp. 5672-5675).
Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0< x<0.13) were prepared on GaAs substrates by low-pressure metal organic vapour phase epitaxy. Magnetic moment measurements indicated that reference epitaxial layer had a Curie temperature of 343K independent on the composition. On the other hand, the quantum dots prepared under Stranski–Krastanov growth mode from the identical gas phase composition showed a lower value of Curie temperature. This value varied from 41 to 235K in relation to the material composition. Moiré fringes at transmission electron microscopy plan view were used for characterization of strain in InMnAs quantum dot structures.
Keywords: PACS; 75.75.Cd; 78.67.Hc; 81.05.Ea; 81.15.GhMagnetic semiconductors; Quantum dots; Curie temperature; Strain
Active oxidation of Cu3Au(110) using hyperthermal O2 molecular beam by Michio Okada; Yuden Teraoka (pp. 5676-5680).
Oxidation of Cu3Au(110) using a hyperthermal O2 molecular beam (HOMB) was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident energy dependence of the O-uptake curve, the precursor-mediated dissociative adsorption occurs, where the trapped O2 molecule can migrate and dissociate at the lower activation-barrier sites, dominantly at thermal O2 exposures. Dissociative adsorption of O2 on Cu3Au(110) is as effective at the thermal O2 exposure as on Cu(110). On the other hand, at the incident energies of HOMB where the direct dissociative adsorption is dominant, it was determined that the dissociative adsorption of O2 implies a higher activation barrier and therefore less reactivity due to the Au alloying in comparison with the HOMB oxidation of Cu(110). The dissociative adsorption progresses with the Cu segregation on Cu3Au(110) similarly as on Cu3Au(100). The growth of Cu2O for 2eV HOMB suggests that the diffusion of Cu atoms also contribute to the oxidation process through the open face, which makes the difference from Cu3Au(100).
Keywords: PACS; 68.43.−h; 68.35.bd; 34.35.+aMolecular beam; Cu; 3; Au; Cu; X-ray photoemission spectroscopy; Oxidation
Composition modulation analysis of In xGa1− xP layers grown on (001) germanium substrates by C.E. Pastore; D. Araújo; M. Gutiérrez; J. Miguel-Sánchez; E. Rodríguez-Messmer (pp. 5681-5683).
The development of new photovoltaic approach to improve costs and efficiencies is focused on the new materials and new technologies. InGaP is, in this sense, a key material for solar conversion. In particular, in the solar concentration approach, this material is part of multiple junction solar cells. Its low lattice mismatch with germanium and its adequate bandgap make it very promising. This paper shows how compositional modulation can affect the InGaP emitter and the AlGaAs tunnel junctions. The influence of the growth conditions, on the compositional modulation and misfit and threading dislocations, in In0.49Ga0.51P layers is demonstrated by TEM on purposely grown single InGaP layers. High resolution electron microscopy (HREM) intensity profiles showed no elastic lattice related modulation.
Keywords: PACS; 68.37.Ef; 81.05.Ea; 88.40.jpElectron microscopy; Photovoltaic; Germanium; InGaP; Phase separation
Studies of resistance switching effects in metal/YBa2Cu3O7− x interface junctions by A. Plecenik; M. Tomasek; T. Plecenik; M. Truchly; J. Noskovic; M. Zahoran; T. Roch; M. Belogolovskii; M. Spankova; S. Chromik; P. Kus (pp. 5684-5687).
Current–voltage characteristics of planar junctions formed by an epitaxial c-axis oriented YBa2Cu3O7− x thin film micro-bridge and Ag counter-electrode were measured in the temperature range from 4.2K to 300K. A hysteretic behavior related to switching of the junction resistance from a high-resistive to a low-resistive state and vice-versa was observed and analyzed in terms of the maximal current bias and temperature dependence. The same effects were observed on a sub-micrometer scale YBa2Cu3O7− x thin film–PtIr point contact junctions using Scanning Tunneling Microscope. These phenomena are discussed within a diffusion model, describing an oxygen vacancy drift in YBa2Cu3O7− x films in the nano-scale vicinity of the junction interface under applied electrical fields.
Keywords: PACS; 74.25.F−; 73.40.Cg; 74.55.+vResistive switching effect; STM; Planar junction; Superconductivity
Effect of annealing on the structural and optical properties of (311)B GaAsBi layers by J.F. Rodrigo; D.L. Sales; M. Shafi; M. Henini; L. Turyanska; S. Novikov; S.I. Molina (pp. 5688-5690).
The influence of post-growth annealing on the microstructure and photoluminescence (PL) of GaAsBi alloys grown on (311)B GaAs is analyzed. Conventional transmission electron microscopy (TEM) performed on as-grown samples evidence the presence of structural defects and a mosaic structure in the GaAsBi layer. A sequence of stacking faults at regions close to the GaAs/GaAsBi interface are observed in high resolution TEM images. After annealing at 473K during 3h the mosaic structure disappears, the presence of defects is reduced and the PL peak intensely enhances.
Keywords: PACS; 68.37.Lp; 68.37.Og; 68.35bgSemiconductor compounds; GaAsBi; Transmission electron microscopy; Molecular beam epitaxy; Photoluminescence
Formation and properties of high density Si nanodots by Jun Xu; Guran Chen; Chao Song; Kunji Chen; Xinfan Huang; Zhongyuan Ma (pp. 5691-5694).
Laser induced crystallization of ultrathin hydrogenated amorphous Si films or amorphous Si-based multilayered structures were used to get high density Si nanodots. The present technique can get size controllable Si nanodots embedded in various dielectric materials with uniform distribution which was revealed by cross-section transmission electron microscopy. Room temperature photoluminescence and electroluminescence were achieved with the emission wavelength in a visible light region both from a-SiN/Si nanodots/a-SiN sandwiched and Si nanodots/SiO2 multilayered structures. The luminescence was associated with the radiative recombination of generated electron–hole pairs in Si nanodots or the luminescent surface states. The electroluminescence intensity is increased with increasing the injection current implying the bipolar carrier injection plays an important role in enhancing the luminescence efficiency. The formed Si nanodots by the present approach can be applied for many kinds of devices such as high efficient light emitting diodes and solar cells.
Keywords: Si nanodots; Laser crystallization; Light emission