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The chemical and electronic structures in the near-surface region of Cu(In,Ga)Se2 thin-film solar cell absorbers are investigated using nondestructive soft and hard X-ray photoelectron spectroscopy. In addition to a pronounced surface Cu-depletion, the [Ga]/([In]+[Ga]) composition indicates that the topmost surface is Ga-poor (or In-rich). For the studied depth region, common depth profiling techniques generally fail to provide reliable information and, thus, the near-surface chemical and electronic structure profiles are often overlooked. The relation between the observed near-surface elemental compositions and the derived electronic properties of the absorber material is discussed. It is found that the surface band gap energy crucially depends on the Cu-deficiency of the absorber surface and suggests that it is, in this region, only secondarily determined by the [Ga]/([In]+[Ga]) ratio.

GaN was grown by the two flow metalorganic chemical vapor deposition method based on monoenergetic positron beams, and defects were studied.

Native defects in InxGa1-xN (x = 0.06-0.14) grown by metal organic chemical vapor deposition were studied using a monoenergetic positron beam. Measurements of Doppler broadening spectra of the annihilation radiation as a function of incident positron energy for InxGa1-xN showed that vacancy-type defects were introduced with increasing InN composition, and the major defect species was identified as complexes between a cation vacancy and a nitrogen vacancy. The concentration of the divacancy, however, was found to be suppressed by Mg doping. The momentum distribution of electrons at the InxGa1-xN/GaN interface was close to that in defect-free GaN or InxGa1-xN, which was attributed to localization of positrons at the interface due to the built-in electric field, and to suppression of positron trapping by vacancy-type defects. We have also shown that the diffusion property of positrons is sensitive to an electric field near the InxGa1-xN/GaN interface. [ABSTRACT FROM AUTHOR]

InxGa1-xN alloys (0 ≤ x ≤ 1) have been grown on GaN/sapphire templates by molecular beam epitaxy. Growth temperature controlled epitaxy was proposed to modulate the In composition so that each InxGa1-xN layer was grown at a temperature as high as possible and thus their crystalline quality was improved. The bandgap energies of the InxGa1-xN alloys have been precisely evaluated by optical transmission spectroscopy, where the effect of residual strain and electron concentration (the Burstein-Moss effect) on the bandgap energy shift has been considered. Finally, a bowing parameter of ∼1.9 ± 0.1 eV has been obtained by the well fitting In-composition dependent bandgap energy. [ABSTRACT FROM AUTHOR]

Infrared reflectivity and Raman spectroscopy were used as two complementary experiments to probe the zone center optical phonons in the aluminum gallium nitride (AlxGa1-xN) systems. A careful analysis of the infrared reflectivity data using the Kramers-Kronig technique and classical dispersion theory gives several resonance modes shifting in frequency with the mole fraction of the aluminum content in the alloy. A signature of an additional resonance mode appears for x∼0.58. A geometrical arrangement was performed to observe the E2 and A1(LO) phonons from the first order Raman scattering. The variation of the frequencies of these phonons was followed in the compositional range investigated. In addition to these two phonons observed from the Raman scattering, a new phonon mode shows up for x∼0.4. Our experimental results were compared with a theoretical study of the lattice dynamics of random AlxGa1-xN alloy based on the generalization of the modified random-element isodisplacement and rigid-ion model in order to interpret the experimentally observed resonance modes. The two-mode behavior in the AlxGa1-xN alloy was observed only for the E1(TO) optical mode. [ABSTRACT FROM AUTHOR]

Impurities in ZnO specimens, including targets for pulsed laser deposition and thin films resulting from their use, were analyzed by secondary ion mass spectroscopy (SIMS). Negatively charged complex ions bound with oxygen ([sup 71]Ga[sup 16]O[sup -] and [sup 14]N[sup 16]O[sup -]) were found to be the most reliable species with which to evaluate the Ga and N content of ZnO films by clarifying possible mass interference effects in SIMS analysis. Calibrations were carried out to determine the Ga concentration (C[sub Ga]) and the nitrogen concentration (C[sub N]) by normalizing the signal intensities for [sup 71]Ga[sup 16]O[sup -] and [sup 14]N[sup 16]O[sup -], respectively, to that for [sup 70]Zn[sup 16]O[sup -]. Alternative ablation of pure single crystal and Ga-doped ceramic ZnO targets was found to be effective not only for achieving systematic control of the Ga concentration in ZnO:(Ga,N) films, but also for minimizing the contamination of undesired impurities from the sintered targets. The substrate temperature plays a decisive role in control of C[sub N] due to a thermally activated desorption process of N-related species during deposition. Systematic control of the C[sub N]/C[sub Ga] ratio in a ZnO:(Ga,N) film was carried out on a ScA1MgO4 substrate by introducing a controlled temperature gradient on the substrate during deposition. A region with the correct concentration ratio of C[sub N]/C[sub Ga]=2, where p-type conduction of the ZnO film was theoretically predicted, was included in the composition spread sample in which the C[sub N]/C[sub Ga] ratio was continuously varied over a wide range. [ABSTRACT FROM AUTHOR]

The growth of low-temperature (LT) GaN buffer layers on sapphire substrates was systematically studied using x-ray photoelectron spectroscopy with regards to processes such as substrate treatment and deposition conditions, along with annealing treatments of the GaN buffer layer during two-step metalorganic chemical vapor deposition. Variations observed in the LT-buffer layer depended strongly on both the chemical state of the sapphire surface as a result of the substrate treatment and the subsequent annealing conditions. A 20 nm buffer layer on non-nitrided sapphire evaporated after the formation of islands during the conventional annealing process (N[sub 2], H[sub 2], and NH[sub 3] gas mixture). Adding H[sub 2] gas to the annealing ambient enhanced the evaporation and reduced the surface coverage. It was found that Al[sub x]Ga[sub 1 - x]N was formed at the interface, which has a low evaporation coefficient. In contrast, a buffer layer deposited onto a nitrided sapphire substrate evaporated completely in a layer-by-layer mode. The buffer layer contained domains with N face (-c) polarity that were almost covered with a Ga face (+ c) layer. It was found that using Ga-rich conditions (a lower V/III ratio) for the deposition suppressed the formation of the -c domains, even on the nitrided sapphire. High temperature (HT) GaN layers were deposited on these well-defined LT-buffer layers. The influence of the various conditions used in preparing the LT-buffer layer on the HT-GaN layers are discussed in terms of the crystalline quality and the polarity of the HT-GaN layers. [ABSTRACT FROM AUTHOR]

Etching characteristics of nondoped GaN films with the polar surface in KOH solution have been investigated. It is confirmed that the continuous etching in KOH solution takes place only for the GaN films with N-face (-c) polarity independent of the deposition method and growth condition. It is found by x-ray photoelectron spectroscopy (XPS) analysis for the Ga face (+c) and N-face (-c) GaN films that the atomic composition of the +c surface is not changed before and after dipping in KOH solution and that on the other hand, the amount of oxygen (oxide) on the -c surface is significantly decreased by the etching. It is also found that the band bending increases by -0.4±0.2 and 0.6±0.2 eV for the +c and -c surfaces after etching, respectively. This is discussed in terms of the surface chemistry. Based on the XPS result, the selective etching of the GaN polar surface is pointed out to originate from bonding configuration of nitrogen at the surface. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the dependence of polar direction of GaN film on growth conditions. Deposition of GaN films on a nitrided sapphire by metalorganic chemical vapor deposition; Change in surface morphology; Relationship between surface morphology and polarity; Substrate nitridation and GaN polarity.

The zone center optical phonons in the aluminum gallium nitride ([Al.sub.x][Ga.sub.1-x]N) systems are investigated by using infrared reflectivity and Raman spectroscopy. The wurtzite lattice vibration of the [Al.sub.x][Ga.sub.1-x]N solid solutions is found to display a two-mode behavior of the transverse E1 phonon mode and a one-mode behavior of the other phonon modes.

Etching characteristics of nondoped GaN films with the polar surface in KOH solution are investigated. It is confirmed that the continuous etching in KOH solution takes place only for the GaN films with N-face polarity independent of the deposition method and growth condition.

Global energy consumption is projected to increase, even in the face of substantial declines in fossil energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. Currently the world's growing thirst for oil amounts to almost 1000 barrels a second. The ever increasing world energy demand cannot be satisfied much longer with fossil fuels. Achieving solutions to energy problem that we face today requires long-term potential actions for sustainable development. In this regard, renewable energy (RE) resources appear to be crucial and the one of the most efficient and effective solutions for sustainable development. That is why a shift to a more sustainable mix by means of the use of RE sources, an increase of the energy efficiency, energy sobriety and greenhouse gas mitigation measures is needed. The development of technological innovation in the energy fields is central to the success of the energy paradigm shift worldwide. Among RE resources, solar energy is by far the largest untapped resource and major primary energy exploitable resource. Algeria has the highest average solar radiation per square meter of any country in the world and is an interesting case study in that it had quite a slow start in this field but is now forging ahead with RE -at least at the utilities level, boosted by government policy. Progress at residential level is not as fast, though. This has to be rectified for the country to meet the targets set in its National Development Plan. A broad range of intensive and promising research and development is being conducted, under the Sahara Solar Breeder (SSB) project concept, in order to produce technological options that can allow energy security, climate stabilisation and economic development from solar energy. In view of the intermittency of insolation, SSB project provides an especially attractive approach in which solar energy must be dispatched on demand to the end user using High Critical Temperature Supra Conductor (HTcSC) cables. The magnitude of such implied infrastructure transition suggests the need for massive investments in innovative energy research. Anticipated patterns of future energy use and consequent environmental impacts are comprehensively discussed in this article. Also, potential solutions to current problems are identified along with the adoption of the SSB project plan and activities. The relations between RE and sustainable development are described with practical cases of SSB energy policy and its portfolio directed towards continental and global clean energy supply with existing solar grade Silicon production from Sahara sand and diatoms technologies making photovoltaic (PV) a significant contributor within a portfolio of energy sources in the coming 10 to 50 years. An illustrative example of some developed SSB key innovative technologies is presented and more should be challenged together, Algerian and Japanese SSB research teams, to seek the paradigm shift in global energy production and transport system. In both cases, the research is emanating from the University of Sciences and Technology of Oran (USTO-MB) in line with Saida University. [ABSTRACT FROM AUTHOR]