J. Santamaria

CuInSe2 thin films produced by rf sputtering in Ar/H2 atmospheres

Structural, compositional, optical, and electrical properties of CuInSe2thin filmsgrown by rf reactive sputtering from a Se excess target in Ar/H2 atmospheres are presented. The addition of H2 to the sputtering atmospheres allows the control of stoichiometry of films giving rise to remarkable changes in the film properties. Variation of substrate temperature causes changes in film composition because of the variation of hydrogen reactivity at the substrate. Measurements of resistivity at variable temperatures indicate a hopping conduction mechanism through gap states for films grown at low temperature (100–250 °C), the existence of three acceptor levels at about 0.046, 0.098, and 0.144 eV above valence band for films grown at intermediate temperature (250–350 °C), and a pseudometallic behavior for film grown at high temperatures (350–450 °C). Chalcopyrite polycrystalline thin films of CuInSe2 with an average grain size of 1 μm, an optical gap of 1.01 eV, and resistivities from 10− 1 to 103 Ω cm can be obtained by adding 1.5% of H2 to the sputtering atmosphere and by varying the substrate temperature from 300 to 400 °C.

Lithium insertion in Ba2YCu3O7-y

Novel materials, LixBa2YCu3O7-y(0≤x≤2), have been obtained by reaction of Ba2YCu3O7-y with n-butyl lithium. The most striking feature of these materials is the coexistence of both ionic conductivity and superconductivity for 0<x<0.5. Transmission electron microscopy (TEM) and electron diffraction show the lithiation to occur anisotropically.

Structural, electrical, and optical properties of CuGaSe2 rf sputtered thin films

Thin films of CuGaSe2 have been produced by rf sputtering. Compositional, structural, electrical, and optical properties are strongly influenced by growthtemperature. At substrate temperatures lower than 300 °C amorphous or poorly crystalline Se‐excess films are obtained, showing high resistivity (≊103 Ω cm) and optical transitions at 1.62, 1.80, and 2.4 eV (values lower than the single‐crystal counterparts). At the higher growthtemperatures,polycrystalline films are obtained (average grain size 0.7 μm) with lower values of resistivity (1 Ω cm), and optical transitions at 1.68, 1.90, and 2.55 eV (very close to the single‐crystal values). A hopping conduction mechanism has been detected at the lower measuringtemperature (T 150 K). Structural and compositional characteristics are used to explain the behavior observed in the electrical and optical properties.

Ionic conductivity of lithium inserted Ba2YCu3O7−y

Abstract Dielectric response experiments, varying the temperature of lithium inserted Ba 2 YCu 3 O 7−y samples, have been performed to search an ionic conduction mechanism. The study showed that Ba 2 YCu 3 O 7−y becomes ionic conductor by lithiation at temperatures higher than 400 K. The activation energies for the electronic and ionic conduction processes resulted to be 0.17 and 0.7 eV, respectively.

Sputtering of SiO2 in O2Ar atmospheres

Abstract The r.f. sputtering of SiO 2 in an ArO 2 atmosphere was studied. The study was carried out to improve the insulating properties of films relative to those produced in a pure argon discharge which showed a clear aging effect on the losses. The O 2 percentage was varied in the range 1%–4% of the total pressure. The improvement in the insulating properties consisted mainly in a stabilization of the electrical properties close to the best values reported for SiO 2 . The role of the oxygen is explained on the basis of annihilation of defects associated with oxygen vacancies in the SiO 4 tetrahedral chains.

Dielectric response and ionic conductivity of Cs(NbTe)O6

Abstract A study of the dielectric response in the frequency range 10 Hz to 10 7 Hz has been conducted on Cs(NbTe)O 6 defect pyrochlore oxides. Two different behaviours are identified: one characteristic of a volume conduction process by Cs + ions and other due to a contact effect. Ionic conductivity is derived from complex impedance plots and an activation energy of 0.67 eV is deduced for ion motion.

Synthesis, characterization and ionic conductivity of Tl(NbTe)O6

Abstract Mixed oxide Tl(NbTe)O 6 is prepared by solid state reaction from Te(OH) 6 , Nb 2 O 5 and TlNO 3 . This material is characterized by powder X-ray diffraction. From the X-ray analysis, the atomic positions and R discrepancy factors are also calculated. The a.c. dielectric response is analyzed, resulting in two different dispersive behaviours at different temperatures and frequency ranges. The activation energy for ionic conduction is obtained.

Thin CuxS sputtered films in Ar/H2 atmospheres

Abstract The effect of hydrogen added to the rf argon discharge on the physical properties of thin Cu x S films produced by rf sputtering from a Cu 2 S target is studied. Hydrogen content ranged from 0 to 5% of the total pressure. Electrical, structural and optical properties of films are analysed as a function of the hydrogen percentage and correlated with different processes taking place in the target and in the plasma which are monitored by glow discharge optical and mass spectroscopies (GDOS and GDMS). The produced films show resistivity values between 10 −4 and 10 2 Ω · cm, depending on the hydrogen content during the growth, and they are correlated with X-ray diffraction measurements.

Effects of residual gases and rf power on ITO rf sputtered thin films

Abstract A study of the influence of gas composition and applied rf power on the sputtering of an ITO compound target in Ar atmosphere is shown. The use of glow discharge optical and mass spectroscopies has allowed us to avoid the lack of reproducibility in film properties and deposition rate due to water desorption from the target surface. Hence, the study of rf power influence on film properties is made more easily. The influence of both power related effects namely heating and electron bombardment is analysed. Optimization of the process allowed us to obtain resistivities down to 5 × 10−4 Ω cm, mobilities up to 35 cm2 (V s)−1 and average transmittance of 95% in films 0.5 μm thick.

Barrier effects on ionic conductivity and dielectric response of Tl(NbTe)O6

Abstract Complex impedance measurements in the frequency range 10-10 7 Hz and at temperatures ranging between 298 K and 800 K have been performed on Tl(NbTe)O 6 powder samples. Complex impedance plots are strongly affected by grain boundaries. An analysis of the dielectric response in the permittivity representation allows to distinguish between bulk and barrier contributions.