Effects of experimental parameters on composition of boron carbon nitride thin films deposited by magnetron sputtering

We have synthesized boron carbon nitride thin films by radio frequency magnetron sputtering. The films structure and composition were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the three elements of B, C, N are chemically bonded with each other and atomic-level hybrids have been formed in the films. The boron carbon nitride films prepared in the present experiment possess a disordered structure. The influence of PN₂/PN₂+Ar, total pressure and substrate bias voltage on the composition of boron carbon nitride films is investigated. The atomic fraction of C atoms increases and the fractions of B, N decrease with the decrease of PN₂/PN₂+Ar from 75% to 0%. There is an optimum total pressure. That is to say, the atomic fractions of B, N reach a maximum and the fraction of C atoms reaches a minimum at the total pressure of 1.3 Pa. The boron carbon nitride films exhibit lower C content and higher B, N contents at lower bias voltages. And the boron carbon nitride films show higher C content and lower B, N contents at higher bias voltages.     

Large area mapping of the alloy composition of Alx Ga1–x N using infrared reflectivity

The energy position of a dip observed in the IR‐reflectance spectra recorded from wurtzite c ‐plane Al_x Ga_1–x N epitaxial films grown on SiC substrate reflects the composition of the alloy. A calibration procedure is presented with the possibility of mapping for large area wafer. The technique is non‐destructive, scalable and fast. The limitations are discussed and comparisons with other techniques are made. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of photoexcited plasma in p-doped GaAs beveled structures by micro-Raman spectroscopy

The generation and properties of photoexcited steady-state plasma of electrons and holes in bevel-shaped p-type GaAs structures were studied by micro-Raman spectroscopy. The best correspondence of theoretical calculations with experimental spectra was obtained by using of photoexcited carrier concentration of 1.1 × 10¹⁷ cm⁻³ and mobility 600 and 40 cm²/V s for the photoexcited steady-state electrons and holes, respectively. The analysis of the plasma behavior and its coupling with longitudinal optical phonons at different positions along the bevel shows that the mode resulting from this coupling causes the changes of Raman intensities recorded in frequency positions of transversal (TO) and longitudinal (LO) optical phonon peaks. These changes were further studied and physical interpretation was provided. The dependence of their ratio in the region affected by surface depletion layer can be fitted by linear function very well. The linearity was observed at all studied structures. This behavior on beveled structures prepared by special treatment with very low bevel angle can be used for analysis of the p-type GaAs nanostructures, particularly for measurement and extraction of a doping profile of p-type impurities in GaAs with very high resolution in nm scale.     

Influence of direct current plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper films

Physical vapor processes using glow plasma discharge are widely employed in microelectronic industry. In particular magnetron sputtering is a major technique employed for the coating of thin films. This paper addresses the influence of direct current (DC) plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper (Cu) thin films coated on silicon substrates. The influence of the sputtering parameters including DC plasma power and argon working gas pressure on the electrical and structural properties of the thin Cu films was investigated by means of surface profilometer, four-point probe and atomic force microscopy.     

Synthesis of silicon carbide films by combined implantation with sputtering techniques

Silicon carbide (SiC) films were synthesized by combined metal vapor vacuum arc (MEVVA) ion implantation with ion beam assisted deposition (IBAD) techniques. Carbon ions with 40 keV energy were implanted into Si(1 0 0) substrates at ion fluence of 5 × 10¹⁶ ions/cm². Then silicon and carbon atoms were co-sputtered on the Si(1 0 0) substrate surface, at the same time the samples underwent assistant Ar-ion irradiation at 20 keV energy. A group of samples with substrate temperatures ranging from 400 to 600 °C were used to analyze the effect of temperature on formation of the SiC film. Influence of the assistant Ar-ion irradiation was also investigated. The structure, morphology and mechanical properties of the deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation, respectively. The bond configurations were obtained from IR absorption and Raman spectroscopy. The experimental results indicate that microcrystalline SiC films were synthesized at 600 °C. The substrate temperature and assistant Ar-ion irradiation played a key role in the process. The assistant Ar-ion irradiation also helps increasing the nanohardness and bulk modulus of the SiC films. The best values of nanohardness and bulk modulus were 24.1 and 282.6 GPa, respectively.     

Formation of p-type ZnMgO thin films by In-N codoping method

In-N codoped ZnMgO films have been prepared on glass substrates by direct current reactive magnetron sputtering. The p-type conduction could be obtained in ZnMgO films by adjusting the N₂O partial pressures. The lowest resistivity was found to be 4.6 Ω cm for the p-type ZnMgO film deposited under an optimized N₂O partial pressure of 2.3 mTorr, with a Hall mobility of 1.4 cm²/V s and a hole concentration of 9.6 × 10¹⁷ cm⁻³ at room temperature. The films were of good crystal quality with a high c-axis orientation of wurtzite ZnO structure. The presence of In-N bonds was identified by X-ray photoelectron spectroscopy, which may enhance the nitrogen incorporation and respond for the realization of good p-type behavior in In-N codoped ZnMgO films. Furthermore, the ZnMgO-based p-n homojunction was fabricated by deposition of an In-doped n-type ZnMgO layer on an In-N codoped p-type ZnMgO layer. The p-n homostructural diode exhibits electrical rectification behavior of a typical p-n junction.     

X-ray absorption spectroscopy study of pulsed-laser-evaporated amorphous carbon films

Amorphous carbon (a-C) films obtained by pulsed-laser ablation of graphite have been investigated by X-ray Absorption Spectroscopy (XAS). The onset of 1s ^* transitions in the films lies in the gap between the ^* and ^* bands in graphite and very close to the absorption edge of diamond, indicating a high content ofsp ³ hybridization. A sharp feature at this onset is observed and assigned to a core exciton insp ³-hybridized disordered C atoms. Its shift of 0.5 eV with respect to the core exciton in diamond is probably due to a higher localization of the excited electron induced by disorder. A small peak coming from C–H bonds at the surface is observed and its intensity inereases with the amount ofsp ³-hybridized atoms in the sample. This can be easily explained by associating a higher amount of dangling bonds at the surface to a highersp ³ content. Polarization-dependent XAS measurements show that the angular distribution of these C–H bonds has a mean value close to the normal to the surface.     

Investigation of structural phase transition in polycrystalline SrTiO3 thin films by Raman spectroscopy

Polycrystalline SrTiO₃ thin films were prepared by pulsed laser deposition technique. The phonon properties and structural phase transition were studied by Raman spectroscopy. The first-order Raman scattering, which is forbidden in SrTiO₃ single crystal, has been observed in the films, due to the structural distortion caused by strain effect and oxygen vacancies. The Fano-type line shape of TO₂ phonon reveals the existence of polar microregions in the STO thin films. The evolution of TO₂ and TO₃ phonons with temperature shows the occurrence of a structural phase transition at 120 K related to the formation of polar macroregions in the films.     

Properties of NiO thin films deposited by chemical spray pyrolysis using different precursor solutions

NiO thin films have been deposited by chemical spray pyrolysis using a perfume atomizer to grow the aerosol. The influence of the precursor, nickel chloride hexahydrate (NiCl₂·6H₂O), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel hydroxide hexahydrate (Ni(OH)₂·6H₂O), nickel sulfate tetrahydrate (NiSO₄·4H₂O), on the thin films properties has been studied. In the experimental conditions used (substrate temperature 350 °C, precursor concentration 0.2-0.3 M, etc.), pure NiO thin films crystallized in the cubic phase can be achieved only with NiCl₂ and Ni(NO₃)₂ precursors. These films have been post-annealed at 425 °C for 3 h either in room atmosphere or under vacuum. If all the films are p-type, it is shown that the NiO films conductivity and optical transmittance depend on annealing process. The properties of the NiO thin films annealed under room atmosphere are not significantly modified, which is attributed to the fact that the temperature and the environment of this annealing is not very different from the experimental conditions during spray deposition. The annealing under vacuum is more efficient. This annealing being proceeded in a vacuum no better than 10⁻² Pa, it is supposed that the modifications of the NiO thin film properties, mainly the conductivity and optical transmission, are related to some interaction between residual oxygen and the films.     

Auger electron spectroscopy depth profiling of Fe-oxide layers on electromagnetic sheets prepared by low temperature oxidation

Auger electron spectroscopy depth profiling was applied to characterize the Fe-oxide layers prepared by low temperature oxidation of Fe electromagnetic sheets produced on an industrial line for applications in the field of electrical motors. In addition the surface morphology, layer composition and layer structure were analysed by electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. We found that the oxide layers on Fe-sheets with good adhesion between the oxide layer and Fe-substrate, consist mainly of magnetite and to a smaller extent of haematite; the layers are typically thinner than 1 μm and the interface between the oxide layer and the Fe-substrate is relatively broad, i.e. up to 0.3 μm. On the contrary, a decrease of adhesion between the oxide layer and the Fe-substrate was found when the layer is thicker than 1 μm and the layer/substrate interface is narrow and contaminated by foreign elements.     

Correlation between density and structure. in boron nitride thin films by X-ray diffraction

* _ion=100 eV. Above E^* _ion the average density (deduced from X-ray reflectivity) shows a strong increase, indicating the sudden appearance of the cubic boron nitride phase consistent with the sp³ concentration deduced from IR absorption spectroscopy. The in-plane X-ray diffraction shows that this cubic phase consists of small nanocrystals of 70 Å linear size. Received: 26 November 1996/Accepted: 27 January 1997     

Epitaxial growth of yttria-stabilised zirconia buffer layers on X-cut LiNbO3 for superconducting electrodes

We report on the epitaxial growth of yttria-stabilised zirconia (YSZ) buffer layers on X-cut LiNbO₃ (LNO) single crystals by pulsed laser deposition. Despite the low chemical stability of the substrates at high temperature, high quality fully reproducible films were obtained over a relatively broad range of processing conditions. The films were (00h) out-of-plane single oriented and the in-plane edge of the YSZ unit cell was aligned with the polar axis of the LNO. However, the YSZ deposition also promoted the formation of the compound LiNb₃O₈. This compound is epitaxial and located at the interface. The homogeneous YSZ film presents a uniform surface, free of outgrowths and with a low roughness. These characteristics are suitable for the epitaxial growth of other oxides, as has been demonstrated with the preparation of YBa₂Cu₃O₇/CeO₂/YSZ/LNO heterostructures. The superconducting YBa₂Cu₃O₇ films were epitaxial, with the c axis perpendicular to the surface and single in-plane orientation, and presented good transport properties (critical temperatures around 86 K and critical current densities close to 10⁶ A/cm² at 77 K). Received: 5 April 2001 / Accepted: 30 July 2001 / Published online: 30 October 2001     

Investigation of microstructure evolution in Pt-doped TiO2 thin films deposited by rf magnetron sputtering

Pt-doped titanium dioxide or titania (TiO₂) films were grown by rf magnetron sputtering and then annealed in the conventional thermal annealing (CTA) process. Raman spectroscopy was used to characterize the structure of the films deposited. The effect of sputtering parameters was studied in focus of the nucleation sites energies (influenced by the substrate temperature) and substrate bombardment energies (influenced by the sputtering pressure or rf power). The X-ray diffractions technique was used to investigate the structural variation after the films were annealed at different temperatures. It was found that 0.75% Pt-doped TiO₂ film exhibits better thermal stability and smaller grain sizes than 0.35% Pt-doped TiO₂ film, suggesting that the suppression of crystallization can be expected with a proper increase of Pt doping level. And the obtained optical transparency higher than 80% even after annealing has demonstrated the films’ prospect for future developments.     

Growth of a textured quasicrystalline phase in Ti-Ni-Zr films prepared by pulsed laser deposition

The preparation in thin film form of the known icosahedral phase in Ti-Ni-Zr bulk alloys has been investigated as a function of substrate temperature. Films were deposited by pulsed laser deposition on sapphire substrates at temperatures ranging from room temperature to 350 °C. Morphological and structural modifications have been followed by grazing-incidence and θ–2θ X-ray diffraction, transmission electron diffraction and imaging. Chemical composition has been analyzed by electron probe microanalysis. The in-depth variation of composition has been studied by secondary neutral mass spectroscopy. We show that pulsed laser deposition at 275 °C makes the formation of a 1-μm-thick film of Ti-Ni-Zr quasicrystalline textured nanocrystallites possible. Received: 7 June 2001 / Accepted: 18 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +33-3/8357-6300, E-mail: brien@mines.u-nancy.fr     

Microstructure and mechanical properties of CrN films fabricated by high power pulsed magnetron discharge plasma immersion ion implantation and deposition

CrN films with strong adhesion with the substrate have been fabricated on Ti6Al4V alloy using novel plasma immersion ion implantation and deposition (PIII&D) based on high power pulsed magnetron sputtering (HPPMS). A macro-particle free chromium plasma is generated by HPPMS while the samples are subjected to high voltage pulses to conduct PIII&D. The CrN coatings have a dense columnar structure and low surface roughness. The grains in the films have the face-center cubic (fcc) structure with the (2 0 0) preferred orientation. An excellent adhesion is achieved with a critical load up to 74.7 N. An implantation voltage of 18 kV yields a hardness of 18 GPa and better wear resistance and a low friction coefficient of 0.48 are achieved.     

The effect of Be-doping structure in negative electron affinity GaAs photocathodes on integrated photosensitivity

A new structure of GaAs photocathode was introduced. The Be-doping concentration is variable in the new structure compared with the constant concentration of Be in the normal photocathode. Negative electron affinity GaAs photocathodes were fabricated by alternate input of Cs and O. The spectral response results measured by the on-line spectral response measurement system show that the integrated photosensitivity of the photocathodes with the new structure is enhanced by at least 50% as compared to those with the monolayer structure. Accordingly, two main factors leading to the enhanced photosensitivity of the photocathodes were discussed.     

Growth and optical characterization of single quantum well structure of submonolayer ZnS/ZnTe

Single quantum wells of submonolayer ZnS/ZnTe were grown between ZnTe layers using hot wall epitaxy method with fast-movable substrate configuration. As ZnS well widths decrease from 1 to 0.15 monolayer, the photoluminescence peaks shift to higher energies from 2.049 to 2.306 eV, and the photoluminescence intensities increase. As ZnS well width decrease, the PL spectra show the lower-energy tails and consequently the increased PL FWHMs. This is a result of a convolution of two PL peaks from two-dimensional and zero-dimensional quantum islands, supported by a still lived lower-energy peaks of zero-dimensional quantum islands above 50 K. The energy shift in the power dependence of photoluminescence spectra is proportional to the third root of the excitation density. These behaviors can be described by the formation of submonolayer type-II ZnS/ZnTe quantum well structure, and the coexistence of two-dimensional and one-dimensional islands in ZnS layers.     

Phase formation and control of morphology in sputtered Cu-In alloy layers

The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn₂ phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering.     

Fabrication and characterization of facing-target reactive sputtered polycrystalline TiO2 films

Polycrystalline TiO₂ films were fabricated using dc facing-target reactive sputtering at different sputtering pressures. The films deposited consist of pure anatase phase or a mixture of anatase and rutile and increasing rutile content to some extent deteriorates the crystallinity of the anatase. It was found that the plasma heating effect, which plays the role of substrate heating, is an important factor for the crystallinity of the films in the case of without substrate heating. The roughness of the films increases monotonically with the increase of the sputtering pressure, which can be ascribed to the decrease in the mobility of the impinging particles. UV-vis transmission measurements reveal that the pure anatase films have higher transmittance than those having mixed phases of anatase and rutile. The band gap value decreases from ∼3.35 to 3.29 eV owing to the increase in the fraction of rutile phase.     

Optical parameters in SnO2 nanocrystalline textured films grown on p-InSb (111) substrates

Spectroscopic ellipsometry and photoluminescence (PL) measurements on SnO₂ nanocrystalline textured films grown on p-InSb (111) substrates by using radio-frequency magnetron sputtering at low temperature were carried out to investigate the dependence of the optical parameters on the SnO₂ thin film thickness. As the SnO₂ film thickness increases, while the energy gap of the SnO₂ film decreases, its refractive index increases. The PL spectra show that the broad peaks corresponding to the donor-acceptor pair transitions are dominant and that the peak positions change with the SnO₂ film thickness. These results can help improve understanding for the application of SnO₂ nanocrystalline thin films grown on p-InSb (111) substrates in potential optoelectronic devices based on InSb substrates.