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The systematic variations in the structural, optical, and electrical properties of polycrystalline Cu͑In, Ga͒Se 2 ͑CIGS͒ thin films with Na doping level were investigated. Precise control of the Na concentration in CIGS films was demonstrated using alkali-silicate glass thin layers of various thicknesses deposited on substrates prior to CIGS growth. The CIGS grain size was observed to decrease with increasing Na concentration, although the surface morphology became smoother and exhibited a stronger ͑112͒ texture, which has been demonstrated consequence of larger grain size. The Ga composition gradient in the CIGS films was found to become large due to the presence of Na during growth, which in turn led to a decrease in the nominal band gap energy. Variations in the photoluminescence spectra and electrical properties suggested that the formation of an acceptor energy state, which may originate from O Se point defects, was enhanced in the presence of Na. This result suggests that not only Na, but also the presence of O in combination with Na contributes to the compensation of point defects and enhances p-type conductivity in CIGS films.

The effects of nitrogen doping into Cu2O thin films deposited by reactive radio-frequency magnetron sputtering were studied. It was found that nitrogen is an effective p-type dopant for Cu2O and the hole density can be controlled from 1×1015 cm-3 to approximately 1017 cm-3. The acceptor level of nitrogen was estimated to be about 0.14 eV by temperature-dependent Hall effect measurements and this value roughly agrees with that obtained by the effective mass theory. No significant degradation of structural and optical properties induced by nitrogen doping were observed. The resistivity of 15.2 Ωcm was obtained for a relatively high nitrogen flow rate, which is the lowest value reported to date for Cu2O thin films.

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Hole traps in p-type Cu 2 O were studied by means of deep level transient spectroscopy in the heterostructure of p-Cu 2 O/i-ZnO/ n-ZnO. In addition to the trap level at about 0.45 eV from the valance band edge, which is already reported as being due to Cu vacancy, we found a new trap level at about 0.25 eV. The new trap is tentatively assigned as Cu-di-vacancy from the trap concentration dependence on oxygen flow rate and substrate temperature. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2175492͔ Cuprous oxide ͑Cu 2 O͒, a direct band gap semiconductor with a band gap energy of 2.0 eV, has been regarded as one of the most promising materials for application to photovoltaic cells, 1,2 especially for the top cell in a tandem structure. The attractiveness of Cu 2 O as a photovoltaic material lies in the fact that the constituent materials are nontoxic, low cost and abundantly available. Cu 2 O / ZnO heterojunction has been fabricated by radio frequency ͑rf͒ magnetron sputtering and showed the photovoltaic effects, but did not demonstrate good performance. 3 Knowledge of defect energies as well as their densities is an important input for further improvement of the performance of Cu 2 O thin film polycrystalline solar cells. There are several reports on the deep trap in Cu 2 O by measuring deep level transient spectroscopy ͑DLTS͒. 4-6 A hole trap with the activation energy of about 0.45 eV from the valence band edge has been observed and assigned as Cu vacancy using Schottky diodes. However, the temperature range in the DLTS measurements was too narrow. It is necessary to measure the DLTS in the expanded temperature range in order to understand the origin of the defect in Cu 2 O. In this work, the DLTS spectra of Cu 2 O with the junction of n-ZnO/ i-ZnO/ p-Cu 2 O structure in the temperature range between 100 and 350 K is reported. We observed a new trap with the activation energy of 0.25 eV from the valence band edge in addition to the 0.45 eV trap, and the origin of the 0.25 eV trap is discussed based on the sample preparation conditions.Polycrystalline p-Cu 2 O/n-ZnO heterostructure was grown by means of rf magnetron sputtering on Corning 7059 glass substrate using a Cu target of 99.99% purity, ZnO target and Ar as sputtering gas. Oxygen was introduced during the growth of Cu 2 O through a nozzle whose end was placed near the substrate. We prepared two sets of samples for Cu 2

The transport of light impurity ions is investigated following neon and nitrogen gas puffing in JET ELMy H-mode. Upon achieving consistency among various ion radiation diagnostics through numerical simulations, the experimental ion transport coefficients are compared with the predictions of neoclassical theory at different regions of the plasma. The convection dominates the transport and, in the core, the transport coefficients approach the neoclassical value.

Deposition conditions of cuprous oxide (Cu2O) thin films on glass substrates by reactive radio-frequency (rf) magnetron sputtering method were studied. The substrate temperature was found to be important for obtaining high-quality films, and the optimum substrate temperature was about 500°C. The Cu2O deposited at 500°C shows a band-gap energy of about 2.0 eV and a typical hole concentration of the order of 1015 cm-3 with a Hall mobility of 60 cm2/V·s, which is the highest mobility reported thus far.

A systematic study on the energy level alignment, chemical interaction, and electron doping at interfaces between bathocuproine (BCP) and various types of metals (Au, Cu, Ag, Mg, and Ca) was carried out by performing ultraviolet photoelectron spectroscopy and electronic conductivity measurements. The energy level alignment at BCP/metal interfaces was found to depend on the metal work function (Φm). For BCP on Au and Cu, whose Φm exceeds 4.3 eV, the energy shift in the highest occupied molecular orbital (HOMO) level with respect to the metal Fermi level (EF) almost accords with the variation in Φm. For BCP on Ag, Mg, and Ca, whose Φm is below 4.3 eV, the HOMO energy level is fixed at 3.7 eV with respect to EF regardless of Φm and new electronic states, called gap states, appeared at BCP/metal interfaces. Since the appearance of gap states is correlated with the energy of the lowest unoccupied molecular orbital (LUMO) level with respect to EF, these states appear to have formed mainly through the interaction with the LUMO. A clear correlation between the density of the gap states and the vacuum level shift suggesting a charge redistribution at BCP/metal interfaces was found. The energy shift in the gap states, which may originate from the variation in the electron occupation of the states, directly affected the electronic conductivity of metal-doped BCP layers (doping metal=Au, Ag, and Ca). These results suggest the electron transfer from the metal EF to gap states plays an influential role in the electrical properties at BCP/metal interfaces.