I. Pepe

Optical determination of the direct bandgap energy of lead iodide crystals

The optical bandgap energy of lead iodide PbI2, grown by Bridgman’s method, is obtained by photoacoustic spectroscopy. Due to its potential applications, as a room temperature, semiconductor material detector, which may be used as a photocell, or as a x‐ and γ‐ray radiation detector, the physical properties of PbI2 have attracted much attention. We computed, by different methods the bandgap energy. We found the energy in a range 2.301±0.038⩽〈Eg〉⩽2.359±0.037 eV.

Electronic and optical properties of lead iodide

The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.

Thermal diffusivity of lead iodide

The thermal diffusivity and thermal conductivity have been determined for lead iodide PbI2, at room temperature, using the photoacoustic spectroscopy. The result shows a thermal diffusivity αs=(25.0±0.4)×10−3u2009cm2/s, a value very close to other semiconductors of current technological importance. The electrical conductivity is also measured and discussed.

Optical properties of 4H-SiC

The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an a ...

Influence of rhodamine 6G doping on the optical properties of TiO2 sol-gel films

Amorphous titanium dioxide (TiO2) thin films doped with rhodamine 6G (R6G) were deposited on glass substrates by the sol-gel process. The optical properties of the films were characterized by photoacoustic, excitation, and fluorescence spectroscopies. The absorption spectra of the R6G-doped TiO2 films exhibited two well-defined absorption regions: an absorption band over 2.0 eV attributed to rhodamine 6G and a band above 3.0 eV corresponding to TiO2 absorption. While the onset of the R6G absorption band was shifted by 0.06 eV towards lower energies as the R6G doping concentration increased within the interval of 0.01–0.10 molu2009%, the onset to high absorption (TiO2 band) for the doped films decreased only by 0.01 eV within the same interval. In addition, the optical absorption of undoped rutile-phase bulk TiO2 was calculated and compared to the experimental results. The estimated theoretical value of rutile TiO2 sample was 3.0 eV. This theoretical result shows good agreement when compared with the experimen...

Sponge-like and columnar porous silicon implanted with nitrogen by plasma immersion ion implantation (PIII)

Sponge-like and columnar porous silicon (PS) were prepared from p- and n-type (100) monocrystalline silicon wafers using different anodization conditions (hydrofluoric acid concentration, current density and anodization time) and then implanted with nitrogen by plasma immersion ion implantation (PIII). The effect of the implantation and of the compounds formed was analyzed by measuring the reflectance of the implanted samples for wavelengths between 220 and 800 nm. A reduction in reflectance in the ultraviolet (UV) region of the spectrum was observed for polished Si samples and for all kinds of PS samples. Increased UV-induced photoluminescence in these samples caused by the increase in absorption in the UV region is expected.

Electrical resistivity of acceptor carbon in GaAs

The resistivity of GaAs implanted with carbon acceptors for concentrations spanning the insulating to the metallic regimes were investigated experimentally and theoretically between room temperatur ...

Modeling and gradient pattern analysis of irregular SFM structures of porous silicon

Technological applications in opto-electronic devices have increased the interest in characterizing porous silicon structure patterns. Due to its physical properties, solutions from KPZ 2D are adopted to simulate the structure of porous material interface whose spatial characteristics are equivalent to those found in porous silicon samples. The analysis of the simulated and real Scanning Force Microscopy (SFM) surfaces was done using the Gradient Pattern Analysis (GPA). We found that the KPZ 2D model presented asymmetry levels compatible with the irregular surfaces observed by means of SFM images of π-Si.

Optical and electronic characterization of the band structure of blue methylene and rhodamine 6G-doped TiO2 sol–gel nanofilms

The optical properties and the band structure of TiO2 sol–gel thin films prepared by the sol–gel process and doped with methylene blue or rhodamine were studied by absorption, excitation and emission spectroscopy. The absorption spectra show two absorption bands, around 2.3 eV and above 3.0 eV suggesting that besides the excitation bands observed in rhodamine at 2.3 eV an efficient energy transfer occurs between the TiO2 conduction band and the molecular rhodamine excited states, yielding a strong emission band at 600 nm, while for methylene blue a strong hypsochromic shift of the absorption bands is observed. The optical absorption and band gap energy for the phase rutile of TiO2 films were calculated with a LDA+U/FPLAPW method, and a comparison of this calculation with experimental data of TiO2 films prepared by undoped sol–gel and sputtering is performed. q 2005 Elsevier Ltd. All rights reserved.

Electrical resistivity and band-gap shift of Si-doped GaN and metal-nonmetal transition in cubic GaN, InN and AlN systems

The critical impurity concentration Nc of the metal-nonmetal (MNM) transition for the cubic GaN, InN and AlN systems, is calculated using the following two different criteria: vanishing of the dono ...