The alumina films are reported to differ in their structure, optical properties and electrical properties depending on the basic atomic structures and the preparation technique. AlxOy thin films in this study were deposited on glass substrates through DC reactive sputtering. The XRD results revealed that the films were amorphous; however, the composition of the films, as analysed by EDX and Raman spectroscopy, depicted the presence of O and Al. The surface morphology analysed by scanning electron microscopy revealed uniform grains with a size ranging between 169 nm and 101 nm subject to power and thickness. The films exhibited optical transmittance above 75

This work reports on successful preparation of thermochromic zirconium and tungsten co-doped vanadium dioxide thin films. The impact of Zr and W co-doping of the thermochromic VO2 thin films on the luminous transmittance and transition temperature of the films is presented. The structural phases and surface morphology of the films were analyzed using the x-ray diffraction and atomic force microscopy, respectively. Two points probe and UV/VIS/NIR Spectrometer were utilized to analyze the films’ electrical and optical properties, respectively. Rutherford backscattering spectroscopy (RBS) was employed to identify the elemental compositions of the films. It was found that Zr and W co-doping of VO2 thin films with 0.3 at

This work investigated the effect of thermal treatment of as-deposited chromium (Cr) thin films in a vacuum and argon/oxygen ambient for effective deposition of spectral selective solar absorber multilayer films. The DC sputtered Cr thin films were thermally exposed at different temperatures in a controlled argon/oxygen environment. Both as-deposited films and those thermally treated in vacuum and in oxygen–argon ambient revealed a weak XRD diffraction peak at 2θ≈44.3° corresponding to (110) plane of BCC structure of Cr metal. Raman analysis revealed one peak at 846 cm−1 corresponding to Cr–O vibration bonds for films thermally treated at 300 °C in a vacuum and 150 °C and 300 °C in argon–oxygen ambient. As determined by AFM and FE-SEM, surface roughness decreased with temperature increase for films thermally treated in a vacuum. Besides, a mixed trend in the evolution of surface roughness was observed for films thermally treated in argon/oxygen ambient. The average spectral transmittance for samples thermally treated in a vacuum decreased with an increase in temperature; however, the samples thermally treated in an argon–oxygen environment exhibited an increasing trend in average spectral transmittance with the increase in temperature. The results clearly show that post-deposition processing at elevated temperatures, particularly in argon–oxygen ambient, influences the structural and optical properties of prior-deposited Cr thin films. This should be considered when designing and depositing multi-layered dielectric/Cr spectral selective solar absorber films.

Indium tin oxide (ITO) thin films were rapid thermal annealed (RTA) for 5 min at a temperature of 550 °C in different exposures of nitrogen gas. Effects of these exposures on the structural, morphological, electrical, and optical properties of these films were investigated using X-ray diffraction, atomic force microscopy and field emission-scanning electron microscopy, four-point probe and hall effect measurements, and ultraviolet–visible-near-infrared (UV–VIS–NIR) spectrophotometer, respectively. The un-exposed RTA ITO films maintained (400) plane preferential orientation similar to the un-annealed sample. However, this plane preferential orientation was reduced relative to (222) plane for exposed RTA sample. The grains and surface roughness parameters were reduced for exposed and enhanced for un-exposed RTA samples as compared to the un-annealed sample. Relatively higher electrical conductivity, average solar transmittance, and bandgap values were observed for ITO films annealed while exposed to nitrogen gas. The exposed RTA ITO films showed sheet resistance of 7.91 Ω sq−1, average solar transmittance of 83%, and bandgap of 3.93 eV. Findings from this study suggest that RTA exposure have the potential to control ITO thin films properties, hence, extending its potential applications.

Copper zinc tin-sulfide (CZTS) films have been widely studied over recent years due to the inherent advantages of low cost, high absorption coefficient (≥ 104 cm−1), suitable band gap (∼1.5 eV) and nontoxicity. In this work, spin coating was used to obtain CZTS films of various compositions and degrees of crystallization on glass substrates, which were then annealed at 500 °C in a N2 atmosphere by using a rapid thermal processing (RTP) furnace in order to optimize their structure. Non-stoichiometric precursors and low spinning speeds resulted in a lower sheet resistance, which is considered to be a result of lower degree of crystallization. Furthermore, the non-stoichiometric films had a high optical band gap (> 1.66 eV) whereas the band gap of the stoichiometric films (1.4 to 1.6 eV) was close to the optimal value (1.5 eV) for solar-cell applications.

High deposition rate ZnO:Al films have been produced at room temperature by reactive DC sputtering using a plasma emission monitoring (PEM) control system. We have investigated the relationship between structural, optical and electrical properties of the ZnO:Al films. Crystal structures of the films have been studied by X-ray diffraction. Optimum ZnO:Al films, with 17-40 Omega/square sheet resistance range and transmittance approaching 88% in the visible region, exhibited a hexagonal ZnO structure with preferential (002) orientation and crystallite sizes of about 27 nm. Resistive transparent films displayed a more random orientation showing peaks at (100) and (102) orientations. Dark "metallic" films were shown to consist of mainly zinc. The optimal ZnO:Al film has been determined from a figure of merit based on power losses due to absorption and series resistance in the ZnO:Al films. It is highly transparent, with low resistance, pronounced (002) peak and large crystallite size. (C) 2012 Elsevier Ltd. All rights reserved.

Seeing a need for more teachers in the sciences, including physics, the Tanzanian government upgraded two teachers' training colleges to become constituent colleges of the University of Dar es Salaam. The government has also been aware of the underrepresentation of women in a number of programs, notably science and engineering. The university created two programs-the Pre-Entry Program and the Female Undergraduate Scholarship Program (FUSP)-to facilitate female enrollment in science courses. In 2007 the physics department, in collaboration with the UNESCO Basic Science Program, conducted a workshop for physics teachers in secondary schools. Of 31 participants, six were female. As a result of these efforts, the number of female students who show interest in physics and other fields of science has increased by 5% since 2002.

We compare the cell efficiency, fill factor and quantum efficiency of Cu(In,Ga)Se-2 based solar cells fabricated using two types of transparent conducting oxide (TCO) top layers. In the first case, Cu(In,Ga)Se-2 solar cells have been fabricated using the RF sputtered ZnO:Al TCO of the established baseline process. Secondly, while maintaining all other layers the same, DC reactively sputtered ZnO:Al replaced the RF sputtered TCO in the solar cell fabrication process. The DC reactive process was controlled by a plasma emission monitoring (PEM) system. The performance of both cells has been studied. The results show that Cu(In,Ga)Se-2 solar cells fabricated using DC sputtered ZnO:Al layers have comparable efficiencies as compared to cells produced using RF sputtered ZnO:Al films. Scanning electron microscopy pictures show that the ZnO:Al layers in both cases have different thickness but similar columnar structure. The highest cell efficiency obtained using the DC and RF sputtered ZnO:Al were 5.6% and 5.5% respectively.;The fill factor and maximum quantum efficiency for Cu(In,Ga)Se-2 solar cells fabricated using DC sputtered ZnO:Al layers were 50.5% and 86% respectively. Cu(In,Ga)Se2 solar cells made-up using RF sputtered ZnO:Al layers had the fill factor of 46.2% and the maximum quantum efficiency of 83%. The Cu(In,Ga)Se-2 absorber layers used in the fabrication of these cells were not representing the best absorber layers produced by the Angstrom solar centre. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

I–V measurements of an as-deposited Ru Schottky barrier diode (SBD) revealed a shift of −0.6 V in the minimum current. This shift is attributed to the presence of localized interface states that modifies the barrier height. Annealing as-deposited and plasma exposed Ru SBDs revealed that the off-set was temperature dependent, suggesting that appropriate selection of anneal temperature may result in reconstruction of the surface, consequently removing the surface states responsible for the distorted I–V response. The effect of hydrogen on the Schottky contact was investigated by exposing the metalized front surface of the SiC to a d.c. hydrogen plasma for 120 min. Capacitance–Voltage (C–V) depth profiles of the H-plasma exposed SBDs revealed a reduction in the near-surface free carrier concentration, suggesting passivation of the Al acceptors by hydrogen. This was confirmed by subsequent reactivation of the electrical activity of the Schottky contact through a series of isothermal reverse bias annealing experiments.

The thermal stability of palladium (Pd) Schottky barrier diodes fabricated on bulk p-type Al-doped (5 - 8 x 10(17) cm(-3)) 6H-SiC is reported. Isochronal anneals revealed a steady improvement in the as-deposited Pd contacts for temperatures up to 250 - 300 degreesC, above which the quality progressively deteriorated. Above 600 degreesC the contacts became unusable. The effect of hydrogen on the Pd Schottky diode was investigated by exposing the Pd metallized surface of the SiC to a hydrogen plasma. It was found that Pd became permeable to hydrogen around 250 degreesC, resulting in a subsequent introduction of hydrogen into the near-surface region of the SiC. Capacitance-voltage (C-V) depth profiles of the H-plasma exposed diodes revealed a partial reduction in the near-surface free carrier concentration, suggesting passivation of the Al acceptors by hydrogen. This was confirmed by subsequent reactivation of the electrical activity of the Schottky contact through a series of isothermal reverse bias annealing experiments. Hydrogen was also found to improve the thermal stability of the Pd Schottky diode.

We report on the passivation by hydrogen and the subsequent thermal reactivation of the acceptors in Al-doped p-type 6H-SiC. Capacitance-voltage measurements revealed that the near-surface free carrier concentration was reduced by at least an order of magnitude after hydrogen plasma treatment. The thermal stability of the Al-H complex in hydrogenated SiC was investigated through a series of isothermal anneals at temperatures ranging from 200 to 275 °C, while applying a reverse bias to a Ru Schottky barrier. Ru was chosen as the Schottky barrier metal for both its permeability to hydrogen as well as its thermal stability. The electric field associated with the applied reverse bias caused the dissociated hydrogen to drift deeper into the material, thereby confirming the positive charge state of atomic H in p-type SiC. The thermal dissociation of the electrically neutral Al-H complex was found to obey first-order kinetics for temperatures above 225 °C with a dissociation energy of (1.51±0.12) eV.

We have investigated the formation of ruthenium Schottky contacts on both n- and p-type 6H-SiC wafers. it is found that Ru forms good quality rectifying contacts, with barrier heights of 0.67 eV and 1.06 eV for n-type and p-type SiC, respectively and ideality factors in the range 1.4 - 1.6. Annealing experiments indicated that the Ru Schottky contacts remained stable up to 450 degreesC, above which a general deterioration in the quality of the contacts (as indicated by an increase in the measured idealities as well as an increase in the reverse bias leakage currents) was observed. It is also shown that the Ru Schottky contact to p-type SiC provides an excellent means through which to introduce hydrogen into the SiC using a hydrogen plasma.