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Vanadium dioxide (VO2) is a well-known phase-changing material that goes from a semiconducting state to a metallic one at a critical temperature of 68 °C, which is the closest to room temperature (25 °C). The electrical transition is also accompanied by structural and optical changes. The optical transition upon heating-also known as thermochromism-makes VO2 a possible coating for “intelligent” windows. In this work, the relationship between the thermochromic performance of VO2 films and the surface morphology was investigated using Temperature-dependent Atomic Force Microscopy (T-AFM) in conjunction with the X-ray Diffraction technique and Scanning Electron Microscopy. In particular, VO2 films were deposited using the rf sputtering technique on Silicon and glass substrates at a substrate temperature of 300 °C, which is one of the lowest for this technique to grow the thermochromic monoclinic phase of VO2. It was found that upon heating (25–100 °C), there was a decrease in RMS roughness for all films independent from the substrate; the value of RMS roughness, however, varied depending on the substrate. Finally, the thermochromic parameters of the VO2 films were correlated with the surface morphology and appeared to be dependent on the kind of substrate used.

ransition metal oxides present a unique category of materials due to their versatile optical, electrical and mechanical properties. Nickel oxide (NiO) is an intrinsic p-type oxide semiconductor. P-NiO with controllable and reproducible physico-chemical properties, if combined with transparency and low temperature (low-T) fabrication processes, can be fully exploited in many transparent and/or flexible devices for applications, like energy management (production, manipulation, storage), sensing, wearable and health care electronics, etc. Reproducibility, transparency and low-T fabrication processes of p-type NiO are the motivation of this work. Nitrogen is one of the dopants used for modifying the properties of NiO. Until now, nitrogen-doped NiO, has shown inferior properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO. The NiO:N films were grown by sputtering on room-temperature substrates in plasma containing 50% Ar and 50% (O2+N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having transmittance less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50-2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheung’s methods. The diode’s transparency and characteristics were further enhanced upon thermal treatment and this was attributed to improved NiO:N properties with annealing. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices.

Broadband time-resolved measurements of pristine and Mg-doped vanadium dioxide (VO2) films are presented herein. The two films were synthesized on float glass and K-glass (SnO2 coated) substrates, respectively. Spectral and temporal dynamics of the insulator to metal transition are accessed via femtosecond pump-probe spectroscopy. Reflection and transmission signals were recorded during sample perturbation by high photon energy, 3.1 eV, laser pulses for below and above the transition threshold values of the excitation fluence. Changes of the spectral dynamics due to photoexcitation are tracked throughout the visible spectrum by use of broadband white-light supercontinuum pulses. The study demonstrates a faster temporal response of the Mg-doped film across the probed spectrum. The system is photoexcited to the metallic state reaching a plateau value in signal transmission within less than 5 ps post-pulse perturbation. These optimized trends of the Mg-doped VO2 films hold promise for applications necessitating ultrafast optical switching capabilities.

Vanadium oxide (VxOy) nanostructured films were prepared by Aerosol Spray Pyrolysis technique with different concentrations of precursor solution (0.005 M, 0.01 M, 0.02 M), using ammonium metavanadate (NH4VO3) as precursor. The deposition was carried out onto glass substrates (Corning glass) at two different substrate temperatures (300 °C and 400 °C). Furthermore, oxalic acid was added to the precursor solution in order to grow the thermochromic VO2(M) monoclinic phase via reduction of the Vanadium oxides in which Vanadium is in a higher oxidizing state. All films were characterized by X-Ray Diffraction technique and UV/Vis/NIR spectroscopy to identify their structural and optical properties, respectively. V2O5 films were tested against ozone, having a sensitivity of 29% in ultra-low concentration of 5ppb ozone, at room temperature. Moreover, nanostructured VO2 films appeared to be thermochromic, having an IR-switching of about 5% at λ = 2500 nm, upon heating.

Nickel oxide (NiO) is a p-type oxide and nitrogen is one of the dopants used for modifying its properties. Until now, nitrogen-doped NiO has shown inferior optical and electrical properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO thin film. The NiO:N films were grown at room temperature by sputtering using a plasma containing 50% Ar and 50% (O2 + N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having a transmittance of less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50–2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheung’s methods, which were further improved upon thermal treatment. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices.

Al-doped NiO (NiO:Al) has attracted the interest of researchers due to its excellent optical and electrical properties. In this work, NiO:Al films were deposited on glass substrates by the radio frequencies (rf) sputtering technique at room temperature and they were tested against ozone gas. The Oxygen content in (Ar-O2) plasma was varied from 2% to 4% in order to examine its effect on the gas sensing performance of the films. The thickness of the films was between 160.3 nm and 167.5 nm, while the Al content was found to be between 5.3at% and 6.7at%, depending on the oxygen content in plasma. It was found that NiO:Al films grown with 4% O2 in plasma were able to detect 60 ppb of ozone with a sensitivity of 3.18% at room temperature, while the detection limit was further decreased to 10 ppb, with a sensitivity of 2.54%, at 80 °C, which was the optimum operating temperature for these films. In addition, the films prepared in 4% O2 in plasma had lower response and recovery time compared to those grown with lower O2 content in plasma. Finally, the role of the operating temperature on the gas sensing properties of the NiO:Al films was investigated.

VO2 is a material of great interest due to its excellent thermochromic properties. In this work, Vanadium dioxide (VO2) films were deposited on commercial SnO2-coated glass by the rf magnetron sputtering technique, at the low deposition temperature of Tsub = 300 °C. The effect of thickness and oxygen content in Ar–O2 plasma on the thermochromic properties were studied. In specific, it was found that the critical transition temperature (Tc) remained constant, while the width of transmittance hysteresis loop (ΔTC) was slightly decreased as thickness was increased from 35 nm to 260 nm. In addition, solar/transmittance modulation (ΔTrsol) was increased by about 6%, while luminous transmittance (Trlum) was decreased almost 30%, with thickness. Furthermore, as the oxygen content in the plasma ranged from 2% to 4%, both TC and ΔTC increased about 4 °C, while ΔTrsol and Trlum showed a slight increase of 1% and 3%, respectively. Finally, ZnO antireflective coatings of thicknesses from 22 to 100 nm were deposited on VO2 thermochromic films by dc magnetron sputtering technique at room temperature, in an effort to enhance the luminous transmittance. As a result, an increase in Trlum of over 8%, with a 30 nm ZnO film was observed, while ΔTrsol was increased by about 1%, independent of the ZnO thickness, while both TC and were unaffected by the presence of ZnO antireflective coating.

Vanadium dioxide (VO2) is a well-known thermochromic material that can potentially be used as a smart coating on glazing systems in order to regulate the internal temperature of buildings. Most growth techniques for VO2 demand high temperatures (&gt, 250 &deg, C), making it impossible to comply with flexible (polymeric) substrates. To overcome this problem, hydrothermally synthesized VO2 particles may be dispersed in an appropriate matrix, leading to a thermochromic coating that can be applied on a substrate at a low temperature (&lt, 100 &deg, C). In this work, we reported on the thermochromic properties of a VO2/Poly-Vinyl-Pyrrolidone (PVP) nanocomposite. More specifically, a fixed amount of VO2 particles was dispersed in different PVP quantities forming hybrids of various VO2/PVP molar ratios which were deposited as films on fused silica glass substrates by utilizing the drop-casting method. The crystallite size was calculated and found to be 35 nm, almost independent of the PVP concentration. As far as the thermochromic characteristics are concerned, the molar ratio of the VO2/PVP nanocomposite producing VO2 films with the optimum thermochromic properties was 0.8. These films exhibited integral solar transmittance modulation (overall wavelengths) &Delta, Trsol = 0.35%&ndash, 1.7%, infrared (IR) switching at 2000 nm &Delta, TrIR = 10%, visible transmittance at 550 nm TrVis = 38%, critical transition temperature TC = 66.8 &deg, C, and width of transmittance hysteresis loop &Delta, TC = 6.8 &deg, C. Moreover, the critical transition temperature was observed to slightly shift depending on the VO2/PVP molar ratio.

ZnO-based n/p homojunctions were fabricated by sputtering from a single zinc nitride target at room temperature on metal or ITO-coated glass and Si substrates. A multi-target rf-sputtering system was used for the growth of all oxide films as multilayers in a single growth run without breaking the vacuum in the growth chamber. The nitrogen-containing films (less than 1.5 at.% of nitrogen) were n-type ZnO when deposited in oxygen-deficient Ar plasma (10% O2) and p-type ZnO when deposited in oxygen-rich Ar plasma (50% O2). The all-oxide homojunction ITO/n-ZnO/p-ZnO/ITO/glass was fabricated in a single deposition run and exhibited visible transparency in the range of 75–85%. The n/p ZnO homojunctions, having metallic contacts, formed on conventionally processed substrates showed a fairly unstable behavior concerning the current-voltage characteristics. However, the same homojunctions formed on Si3N4-patterned substrates and stored in atmosphere for a period of five months were stable exhibiting a turn-on voltage of around 1.5 V. The realization of a room temperature sputtered transparent and stable ZnO homojunction paves the way to the realization of all-oxide transparent optoelectronic devices. Keywords: ZnO homojunction, p-type ZnO, Single step sputtering, Stability, Patterned substrate

VO2 is a well-known thermochromic material that can be potentially applied as a coating on “smart” glazing systems. In this work VO2 thermochromic films, were grown by the rf sputtering technique on two different types of commercial glass substrates, namely fused silica and float glass, at the low deposition temperature of 300 °C. The optimum deposition conditions, in order to succeed the thermochromic monoclinic phase of VO2(M), were investigated and found to be subject to substrate and thickness. It was observed that on the float glass substrate, only films with thicknesses below 50 nm grown with 3% O2 in plasma exhibited a thermochromic behavior, displaying a critical transition temperature of TC = 46.1 °C, width of transmittance hysteresis loop at 2000 nm ΔTC = 9.1 °C, IR-switching ΔTrIR = 14.6%, integrated solar transmittance modulation ΔTrsol = 1.3% and integrated luminous transmittance at 25 °C equal to Trlum = 36.6%. In contrast, films deposited on fused silica glass demonstrated a thermochromic phase, for all thicknesses, when grown with 1% O2 in the plasma. These thermochromic films were characterized by much lower TC(

We report here on an alternative approach for forming p-type transparent conductive oxide ternary alloys Zn–Ir–O (ZIRO) by the means of rf magnetron co-sputtering of Ir and zinc nitride targets in a mixed argon and oxygen plasma. The structural and optical properties of ZIRO thin films formed on both glass and Si (100) substrates have been studied by Energy Dispersive X-ray spectrometry (EDX), X-Ray Diffraction (XRD), Raman and optical spectrophotometry. The EDX results outlined that the Ir incorporation in ZIRO alloys saturates at 3.3% when the rf co-sputtering is done in a plasma containing above 2% O2. XRD and Raman spectroscopy analysis revealed that all films were polycrystalline containing only the ZnO and IrO2 phases. The presence of Ir in ZIRO thin films does affect their optical transparency below 500 nm while it remains comparable to that of ZnO above 500 nm down to the infrared spectral range. Moreover the physical properties of the ZIRO films have been studied after sequentially annealing in air or forming gas (95% N2–5% H2) at elevated temperatures up to 700 °C. All ZIRO films were found to remain highly resistive (MΩ range) regardless of annealing treatment conditions. The optical transparency of these films was found to be further reduced upon annealing at temperatures above 500 °C.

The aim of this paper is the replacing of the expensive sputtering method with the low cost sol–gel one in TCO applications. To this end two sets of indium tin oxide (ITO) thin films are compared and discussed in this paper: one obtained by r.f. sputtering and one by the sol–gel technique and dip-coating. For each of these sets of samples, a series of deposition parameters have been varied in an effort to obtain the most promising optical and electrical properties. Comparative structural, morphological and opto-electrical characterization of sol–gel and sputtered ITO-based films was performed by X-ray diffraction, Scanning electron microscopy, Atomic force microscopy, Spectroellipsometry, UV–VIS Spectroscopy and Hall Effect measurements in order to establish whether the chemical deposition method could lead to thin films with competitive properties as those obtained through the physical method. Comparable, high transmittance (85–90 %) in the VIS–NIR range (250–1050 nm) and carrier concentration values (1020–1021 cm−3) were obtained between sputtered and sol–gel ITO films. The sputtered ITO film in 75 % N2, annealed at 500 °C and the sol–gel 0.1 M ITO film with 10 layers deposited on SiO2/glass exhibit degenerate semiconductor behavior.

International audience; We report on measurement results of a test standard suitable for different microscopic modalities. These findings were obtained by a multimodal hybrid microscope, which requires various calibration methods, also in terms of its further use as a tool in a nanorobotic environment. A Scanning Probe Microscopy (SPM)-Controller based on an FPGA (Field Programmable Gate Array) enables the submicrometer imaging for atomic force and microwave microscopic modalities. It is embedded in an open source software framework for nanorobotics and -automation and is described in this report.

Thermal switching has attracted the research interest during the last decades. Phase Changing Materials (PCM) have the ability to vary their electric conductivity upon external stimuli such as heating and as a result they can be used as thermal switchers in transmission lines. Vanadium dioxide (VO2) is a PCM the electrical conductivity of which can be varied by 3–4 orders of magnitude, undergoing an insulator to metal transition (IMT) at a critical transition temperature of 68 oC. In this work VO2 in the form of powder was synthesized by hydrothermal synthesis and was tested as thermal switching material in as far as the critical transition temperature (TC) of IMT and the width (ΔTc) of IMT hysteresis loop are concerned.

We report on a test standard for different microscopic techniques combined onto one substrate. The patterns of the test standard are recognizable by image processing routines to provide robotic navigation inside Scanning Electron Microscopes. Here it can be used for high-resolution and astigmatism testing. In the center of this standard is a pattern of three different micro capacitance values. This enables high frequency calibration with a Vector Network Analyzer (VNA), one core element of Scanning Microwave Microscopes.

The changes in the optical, microstructural and electrical properties, following the nitrogen incorporation into indium tin oxide thin films are investigated. The films are formed by r.f. sputtering from an indium-tin-oxide (80% In2O3–20% SnO2) target in a mixture of Ar and N2 plasma (75% N2–25% Ar and 100% N2 respectively) on fused silica glass substrate. The impact of rapid thermal annealing (up to 500 °C, in N2 ambient) on the properties of indium tin oxynitride (ITON) thin films is also reported. The UV–vis–NIR ellipsometry (SE) characterization of ITON films was performed assuming several realistic approaches based on various oscillator models, using a chemical composition gradient depth profiling, in agreement with the X-ray photoelectron spectroscopy measurements. The Hall measurements show that the ITON films prepared by r.f. sputtering in 75% N2 and annealed at 500 °C behave as degenerate semiconductors. X-ray diffraction analysis proved that ITON thin films retain an amorphous structure even after RTA at 500 °C in N2 ambient and atomic force microscopy showed the formation of continuous and smooth ITON thin films, with a morphology consisting in quasispherical nanometric particles.

We report the influence of the normal thermal treatment (TT) and of rapid thermal annealing (RTA) on the microstructural, optical and electrical properties of indium tin oxide (ITO) and nitrogen doped indium tin oxide (ITO:N) thin films. The TT was carried out for 1 h at 400 °C and the RTA for 1 min up to 400 °C, both in N2 atmosphere. The ITO and ITO:N films were deposited by reactive sputtering in Argon, and respectively Nitrogen plasma, on Si with (100) and (111) orientation. The present study brings data about the microstructural and optical properties of ITO thin films with thicknesses around 300–400 nm. Atomic Force Microscopy analysis showed the formation of continuous and homogeneous films, fully covered by quasi-spherical shaped particles, with higher roughness values on Si(100) as compared to Si(111). Spectroscopic ellipsometry allowed the determination of film thickness, optical band gap as well as of the dispersion curves of n and k optical constants. X-ray diffraction analysis revealed the presence of diffraction peaks corresponding to the same nominal bulk composition of ITO, but with different intensities and preferential orientation depending on the substrate, atmosphere of deposition and type of thermal treatment.

N-doped ZnO (ZnO:N) thin films, intended to be used as one of the layers in solar cell applications were deposited by r.f. sputtering, using ZnN target (99.9% purity), on silicon and fused silica substrates. In the gas flow composition, Ar was kept constant (50%) and the O 2 /N 2 ratio was varied as: 40%/10%, 25%/25% and 10%/40%. After deposition, rapid thermal annealing (RTA) at 400 and 550 °C for 1 min in N 2 ambient has been performed. The RTA impact on the optical and microstructural properties of ZnO:N thin films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX), UV–vis–NIR spectroscopy, UV–vis–NIR spectroscopic ellipsometry (SE) and infrared ellipsometry (IR-SE). The as-deposited (ad) ZnO:N films are polycrystalline with preferentially oriented columnar crystals. After RTA we found ZnO:N films with improved crystallinity and fewer boundary defects. We report optical constants of ZnO:N from UV to IR spectral range as well as the infrared active phononic modes.

Zinc oxide (ZnO) thin films showing bipolar conductivity were fabricated by sputtering of zinc nitride target in plasma containing mixture of Ar–O 2 gasses. Sputtering in pure Ar plasma produced conductive and opaque zinc nitride (ZnN) films while upon introduction of oxygen up to 30% into the plasma highly transparent single phase polycrystalline n-type ZnO films have been grown. ZnN sputtering in Ar plasma containing more than 30% oxygen produced p-type ZnO films. Hall-effect and photoluminescence measurements revealed the presence of zinc vacancies and nitrogen which are acting as acceptor dopants in p-type ZnO. A heterostructure was fabricated in a single deposition run consisting of n-ZnN and p-ZnO which exhibited rectifying behavior with 2–2.5 V turn-on voltage. Improvements on the formed p/n heterostructure as well as the potential of using single sputtering target in fabrication of Zn-based homo- and hetero-junctions are discussed.

The XeCl excimer laser (308 nm) was used for depositing p-type SrCu 2 O 2 (SCO) films by pulsed-laser deposition (PLD) from undoped and Ba-doped (6%) SCO targets. The SCO films were deposited at 300 °C on glass and p-type Si substrates, while the oxygen pressure was kept constant at 5 x 10 -2 Pa and their properties were investigated just after deposition and after annealing at 330 °C in forming gas. The films were amorphous just after deposition but became stoichiometric SrCu 2 O 2 polycrystalline after annealing and very resistive. The Ba-doped SCO films showed lower transmittance than the undoped ones but for both films the transmittance increased to around 70-80% in the NIR-IR spectrum. The optical energy gap was found to be around 3.24 eV after annealing. SCO films deposited on p-Si exhibited rectifying properties, behaving like p - -SCO/p-Si heterojunctions and their I-V and C-V characteristics were examined with temperature. An explanation of the diode behaviour is attempted based on materials properties and heterodiode characteristics.

Available online 7 February 2009Keywords:Zinc nitrideSputteringTFTOESThin lm In this work we fabricated, by rf magnetron sputtering from a ZnN target, zinc nitride thin lms andexamined their properties in order to be used as channel layer in thin lm transistors. The lms weredeposited at 100 W rf power and the Ar pressure was 5 mTorr. The zinc nitride thin lms were n-type, anddepending on the thickness they exhibited low resistivity (10 10 2 Ohm cm), high carrier concentration(10 18 10 20 cm 3 ) and very low transmittance values due to the excess zinc in their structure. After annealingat 300 °C, in owing nitrogen, the lms became more conductive, but annealing at higher temperaturesdeteriorated the electrical properties and became transparent. Transparent thin lm transistor having zincnitride as channel layer exhibited promising transistor characteristics after nitrogen annealing. Improve-ments in output transistor characteristics due to both material (zinc nitride) and transistor optimization areaddressed.© 2009 Elsevier B.V. All rights reserved.

RF-magnetron sputtering was employed to deposit zinc nitride films, from zinc nitride target, in plasma containing a mixture of Ar–N 2 gases. The effect of ambient atmosphere as well as thermal treatments (annealing in nitrogen and oxidation) on the optical properties of the films were examined. The transparency and conductivity of the films just after deposition were dependent on the amount of Zn in the structure. The films exhibited n-type conductivity and wide optical band gap. Annealing improved their transparency but they became more resistive. Oxygen was detected in films remained in the ambient atmosphere for a long period of time just after deposition, affecting transmissivity. Annealing promoted adsorption of oxygen in their structure, and the optical properties of high temperature annealed films resembled those of zinc oxide films having nitrogen as acceptor dopant. Band-edge emission peaks arising from acceptor exciton as well as nitrogen-related defect centers were revealed by low temperature photoluminescence.

We use the Newton–Raphson method to analyze the optical spectra of indium–tin-oxide and indium–tin–oxynitride films, by deriving the complex refractive index and, thereby, the plasma wavelength and the relaxation time. Reflectance and transmittance as well as partial derivatives of them, necessary for the application of the method, are introduced in analytical form reducing complexity and improving speed. The films we have investigated were deposited on glass by sputtering at different RF power levels. After deposition, they were subjected to annealing at 600 °C and were measured prior to and after that treatment. The results obtained are physically meaningful and lead to useful inferences about the quality of the material in the two different types of the investigated films.

Strontium copper oxide (SCO) has been studied as p-type transparent (VIS) conductive oxide material. Also theoretical studies suggested p-type conductivity of the SrCu2O2 composition. SCO thin layers, with thicknesses of 30–2000 nm, were deposited on glass and silicon substrates both by pulsed laser deposition (PLD) and by MOCVD method. The as-grown layers showed high electrical resistance. Due to an annealing process, the resistivity significantly decreased and the layers showed p-type conductivity. Optical transparency measured on samples grown on glass substrates was found about or above 80%, including also thickness dependence. RBS measurements were applied for the determination of the chemical composition profile of the layers. A comparison revealed some specific differences between as-grown and annealed PLD samples. Due to the annealing, the ratio of oxide phases was changed and a vertical inhomogeneity in chemical composition was observed. Our measurements revealed also the influence of the deposition technique and of the substrate.

SrCu2O2 (SCO) thin films have been fabricated by pulsed laser deposition at oxygen partial pressures between 5 × 10− 5–5 × 10− 2 mbar and substrate temperatures from 300 °C to 500 °C. All films were single-phase SrCu2O2, p-type materials. Films deposited at a substrate temperature of 300 °C and oxygen pressure 5 × 10− 4 mbar exhibited the highest transparency (∼ 80%), having conductivity 10− 3 S/cm and carrier concentration around 1013 cm− 3. Films deposited at oxygen partial pressure higher than 10− 3 mbar exhibited higher conductivity and carrier concentration but lower transmittance. Depositions at substrate temperatures higher than 300 °C gave films of high crystallinity and transmittance even for films as thick as 800 nm. The energy gap of SrCu2O2 thin films was found to be around 3.3 eV.

In this paper, we report first principles calculations and experimental studies of the optical and microstructural properties of both bulk and thin films of SrCu2O2. Polycrystalline SrCu2O2 films were grown by a conventional Pulsed Laser Deposition method in a flowing oxygen environment on corning glass 7059 and silicon substrates. Several characterization techniques, including X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman, spectroscopic ellipsometry, reflectance/transmission spectrophotometry and Atomic Force Microscopy have been used for the investigation of the microstructural and vibrational properties of both bulk and thin films of SrCu2O2. XRD shows that bulk SrCu2O2 is polycrystalline and assumes the pure tetragonal phase of SrCu2O2. The vibrational properties of the tetragonal phase of SrCu2O2 have been inferred from Raman and FTIR spectroscopies and for the first time both Raman and IR active modes have been assigned. The bulk polycrystalline SrCu2O2 optical band gap determined from spectroscopic ellipsometry was 3.34±0.01 eV. XRD results confirmed that pure non-textured polycrystalline phase SrCu2O2 thin films with a smooth surface can be grown by PLD at low temperature

Zinc nitride thin films were deposited by magnetron sputtering using ZnN target in plasma containing either N 2 or Ar gases. The rf-power was 100 W and the pressure was 5 mTorr. The properties of the films were examined with thermal treatments up to 550 °C in N 2 and O 2 environments. Films deposited in Ar plasma were opaque and conductive ( ρ ∼ 10 − 1 to 10 − 2 Ω cm, N D ∼ 10 18 to 10 20 cm − 3 ) due to excess of Zn in the structure. After annealing at 400 °C, the films became more stoichiometric, Zn 3 N 2 , and transparent, but further annealing up to 550 °C deteriorated the electrical properties. Films deposited in N 2 plasma were transparent but very resistive even after annealing. Both types of films were converted into p-type ZnO upon oxidation at 400 °C. All thermally treated zinc nitride films exhibited a shoulder in transmittance at around 345 nm which was more profound for the Ar-deposited films and particularly for the oxidized films. Zinc nitride has been found to be a wide band gap material which makes it a potential candidate for transparent optoelectronic devices.

In the direction of growth of fabricated films, the material near the free surface as well as the interface with the substrate exhibits properties which are different from those of the material in the bulk. The resulting spatial inhomogeneity of the refractive index influences positions and values of the extrema of optical spectra. We exploit this to derive the profile of the refractive index by developing a theoretical approach. In the calculations, taking the derived profile into account, we attain a good reproduction of the experimental Transmittance and Reflectance spectra from approximately 1 to 4 eV, the region of relatively weak refractive-index dispersion.

The surface properties of indium tin oxynitride films prepared by rf-sputtering in nitrogen atmosphere were investigated by X-ray and ultraviolet photoelectron spectroscopy as well as electron energy loss spectroscopy and Auger electron spectroscopy depth profiling. The results are compared to reference measurements on conventional rf-sputtered indium tin oxide films. The incorporated nitrogen is present in different chemical environments. Employing these different spectroscopic techniques, it was found that desorption of nitrogen from the ITON structure upon annealing is the origin of the observed drastical changes in the surface composition and electronic structure. The formation of oxygen vacancies and Sn surface segregation upon annealing is linked to improvements in the physical properties (larger spectral range of transmittance and higher conductivity) of the films.

Indium-tin-oxide (ITO) and indium-tin-oxynitride (ITON) films have been deposited on glass by rf-sputtering from an ITO target, using Ar plasma and N 2 plasma, respectively, and different rf-power. Optical emission spectroscopy (OES) was employed to identify the species present in the plasma and to correlate them with the properties of the ITO and ITON thin films. Emission lines of ionic In could only be detected in N 2 plasma, whereas in the Ar plasma additional lines corresponding to atomic In and InO, were detected. The deposition rate of thin films was correlated with the In species, rather than the nitrogen species, emission intensity in the plasma. The higher resistivity and lower carrier concentration of the ITON films, as compared to the respective properties of the ITO films, were attributed to the incorporation of nitrogen, instead of oxygen, in the ITON structure.

Micro- and nanomechanical AlN and 3C-SiC resonator beams with resonant frequencies between 20 kHz and 2 MHz, depending on the resonator geometry, have been realized and characterized at ambient conditions. Up to 200 nm thin epitaxial group III-nitrides and SiC layers were grown on silicon (111) and (100) oriented substrates, respectively. The beams were dry-etched by an electron cyclotron resonance (ECR) plasma and an inductive coupled plasma (ICP) technique. The freestanding resonator bars have dimensions in the sub-μm to nm-range. The operation principle based on the known magneto motive actuation and a thin conductive metal layer on top of the resonator realizes the detection. The main fabrication steps of the resonator beams are presented. The resonant frequencies, the quality factors of the MEMS and NEMS are investigated in dependence on the geometry and the residual strain in the epitaxial layers.

In this study we report results on a series of Si/SiO2 multilayers periods deposited by standard CMOS processes on thermally oxidised Si substrates. Each period was formed by alternating a low-pressure chemical vapour deposition (LPCVD) nanocrystalline silicon thin film and a SiO2 thin film obtained by atmospheric pressure chemical vapour deposition (APCVD). High-resolution TEM (HRTEM) and Raman spectroscopy have been used for the physical characterisation of the nc-Si/SiO2 multilayers. The HRTEM analysis revealed a columnar structure, with an average grain size of 15 nm for the silicon layers. The Si–SiO2 interfaces were smooth with a surface roughness for silicon layers less than 1 nm, as estimated from HRTEM analysis. Raman measurements demonstrate that the nanocrystalline silicon (nc-Si) layers are free-of-stress. Room temperature photoluminescence (PL) spectra, obtained by using a 325 nm continuous wave (CW) laser excitation, showed a broad blue peak centred on 440 nm. The intensity of the blue PL band increased with the number of periods in the nc-Si/SiO2 multilayers. The origin of this intense room temperature blue PL band is discussed.

Indium-tin-oxynitride (ITON) and indium-tin-oxide (ITO) thin films have been fabricated by r.f. sputtering from an indium-tin-oxide target in a plasma containing N2 and Ar gases, respectively. The properties of films grown at two different plasma pressures were examined just after deposition and after annealing. Although the electrical properties of these films were improved after annealing, the properties of the ITON films were still inferior to those of the ITO films. The resistivity of the ITON films after annealing was reduced by a factor of two for the film at the higher plasma pressure, but the carrier concentration was almost the same. The ITON films fabricated at low pressure exhibited a significant blue shift in transmittance, which was not related to the increase carrier concentration after annealing.

We demonstrate that it is possible to reduce significantly the internal polarisation fields in InAlGaN/GaN quantum wells (QWs), provided that the composition of the quaternary layer is appropriate. We have experimentally estimated an internal field of 2.65 mV/A in In 0.085 Al 0.285 Ga 0.63 N/GaN QWs, which is a factor of four smaller than in equivalent GaN/Al 0.15 Ga 0.85 N QWs. Preliminary optical pumping experiments on laser structures using as active medium In 0.085 Al 0.285 Ga 0.63 N/GaN QWs have shown lower threshold than GaN/AlGaN laser structures at room temperature.

Indium-tin-oxide (ITO) and indium-tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N-2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N-2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium-tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed.

We present a study of the properties of III–V structures integrated on Si by low-temperature GaAs–Si wafer bonding, using an intermediate spin-on-glass layer. Transmission electron microscopy revealed the good quality of the bonding and the absence of micro-cracks or dislocations in the semiconductor material. Photoluminescence measurements on GaAs/AlGaAs multiple quantum well structures bonded on Si confirmed that the structural integrity of the quantum wells was preserved during the wafer bonding and thinning process. Photoreflectance measurements at temperatures in the range of 80–300 K showed that the bonded GaAs layers were practically stress free at room temperature, while a tensile stress appeared at lower temperature, due to the different thermal expansion coefficients of GaAs and Si. Laser devices with etched mirrors were fabricated on silicon and exhibited similar performances with reference devices fabricated on a GaAs substrate.

Structures containing silicon nanocrystals (nc-Si) are very promising for Si-based light-emitting devices. Using a technology compatible with that of silicon, a broader wavelength range of the emitted photoluminescence (PL) was obtained with nc-Si/SiO2 multilayer structures. The main characteristic of these structures is that both layers are light emitters. In this study we report results on a series of nc-Si/SiO2 multilayer periods deposited on 200 nm thermal oxide SiO2/Si substrate. Each period contains around 10 nm silicon thin films obtained by low-pressure chemical vapour deposition at T=625°C and 100 nm SiO 2 obtained by atmospheric pressure chemical vapour deposition T=400°C. Optical and microstructural properties of the multilayer structures have been studied by spectroscopic ellipsometry (using the Bruggemann effective medium approximation model for multilayer and multicomponent films), FTIR and UV–visible reflectance spectroscopy. IR spectroscopy revealed the presence of SiOx structural entities in each nc-Si/SiO2 interface. Investigation of the PL spectra (using continuous wave-CW 325 nm and pulsed 266 nm laser excitation) has shown several peaks at 1.7, 2, 2.3, 2.7, 3.2 and 3.7 eV , associated with the PL centres in SiO2, nc-Si and Si–SiO2 interface. Their contribution to the PL spectra depends on the number of layers in the stack.

We performed optical characterisation on high-quality InAlGaN thin films and InAlGaN/GaN quantum wells (QWs) grown by rf-MBE. Our main findings are that the In bowing coefficient in In0.08Al0.29Ga0.63N alloys is found unexpectedly large (bI = 8.4 eV), and that the internal field in In0.08Al0.29Ga0.63N/GaN QWs is strongly reduced (0.25 MV/cm) as a consequence of enhanced polarisation matching between well and barrier layers.

Optimized MBE outgassing procedures eliminated Hillock-type oval defects, allowing the bonding of epitaxial GaAs AlGaAs wafers with Si wafers. The application of a single growth epitaxial structure for the fabrication of laser diode (LD) and photodetector (PD) devices was investigated. Four graded index separate confinement heterostructure-multiquantum well (GRINSCH-MQW) LI) structures with 2, 4, 8 and 16 GaAs quantum wells (QWs) were used to evaluate quantitatively the effect of the number of QWs in the performance of LDs. Threshold current density values of 358 A/ cm 2 for 2 QWs, 484 A/cm 2 for 4 QWs, 685 A/cm 2 for 8 QWs and 1435 A/cm 2 for 16 QWs were measured. PDs were fabricated by five GRINSCH-MQW structures with 2 32 QWs and exhibited responsivity of 0.020 A/W for 2 QWs, 0.031 A/W for 4 QWs, 0.069 A/W for 8 QWs, 0.181 A/W for 16 QWs and 0.350 A/W for 32 QWs.

Reactive ion etching (RIE) was used for the fabrication of GaAs/AlGaAs optoelectronic devices (laser diodes and photodetectors) for optical interconnect applications. Smooth, vertical sidewalls with a smooth surface at the field were obtained after optimizing RIE conditions in BCl 3 -formed plasma. Accurate in-situ monitoring of the etching process was realized by laser interferometry end-point detection. This led to good process control and reproducibility of the demanding fabrication of the optoelectronic devices. The RIE etching process did not affect the electrical properties of the device by increasing the surface recombination currents. Lasers with etched mirrors exhibited a threshold current density of 970 A cm −2 , which is one of the best values ever reported. The feasibility of a simple technology for the fabrication of optoelectronic circuits, based on a BCl 3 RIE process for laser mirror etching, has been demonstrated.

Photodetectors (PDs) based on three separate confinement-multiple quantum well (SCH-MQW) structures (with 2,4 and 8 QWs) and six graded-index (GRIN) SCH-MQW structures were studied for two types of devices: guided wave and non-guided wave devices. Non-guided wave devices were processed and the capacitance and the responsivity, in the wavelength range of 750-900 nm, were determined for various bias voltages. Guided wave PDs were simulated using the transfer matrix method for optical mode calculation and the minimum length of the detectors was calculated for absorbing 99% of the incident light. The junction capacitance of the guided wave PDs was calculated from the measured capacitance of non-guided wave devices and the minimum size of the devices; values of 215,101, and 52 fF were obtained for 2,4 and 8 QW SCH-MQW structures. Laser diodes were also fabricated from the three different SCH-MQW structures. Threshold current densities (Jth) of 737,755 and 1210 A cm-2 were measured for 2,4 and 8 QWs, respectively. Further improvement was achieved using GRINSCH-MQW structures and LDs with 4 QWs exhibited 33% decrease in Jth and 22% increase in slope efficiency. © 2001 Elsevier Science B.V.

The growth and material properties of GaN heteroepitaxial layers on vicinal (1 0 0) and exact (1 1 1)B substrates have been investigated, using molecular beam epitaxy (MBE) with N2 RF-plasma source. We examined the approach to grow GaN directly on the oxide desorbed GaAs, without the incidence of an As beam during oxide desorption or the following stages of growth. Perfect smooth surfaces were obtained on (1 1 1)B GaAs but excellent luminescence properties were observed on vicinal (1 0 0) GaAs. Four growth temperatures (TG) were compared for the (1 0 0) orientation and a monotonic increase of photoluminescence intensity with increasing TG, in the range of 570–680°C, was observed. The best surface morphology of less than 10 nm rms roughness was also determined, by atomic force microscopy, for the maximum (680°C) temperature. The layers exhibited up to 1017 cm−3 electron concentration and it could be compensated by Mg impurities. Metallizations of Pt and Pd gave ohmic contacts on GaN/GaAs (1 0 0) but a Schottky diode contact was achieved by Ir metallization. The obtained material properties are probably sufficient for realizing efficient GaN light emitters on (1 0 0) GaAs substrates.