J. Souza de Almeida

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.

Electronic and optical properties of γ-Al2O3 from ab initio theory

We report on a density functional theory calculation of the electronic structure and optical properties of gamma-Al2O3. We have made a comparison between the optical and electronic properties of th ...

Optical properties of SiGe alloys

The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).

Photoacoustic and transmission studies of SiC polytypes

The optical bandgap energies (OBGE) of 3C, 15R, 6H and 4H-SiC have been investigate experimentally by transmission and photoacoustic spectroscopies. The measurements were performed on 470 mm thick wafers. The OBGE obtained from both spectroscopies for different polytypes show very good agreement. In order to have a better understanding of these materials calculations of eletronic band structure were performed by the full-potential linearized augmented plane wave (FPLAPW) method. For the OBGE the results are compared to the measurements agreeing closely over the energies of those polytypes.

Optical Absorption of Large Band-Gap Sb x Bi 1- x I 3 Alloys

ABSTRACT The optical properties of SbBiI 3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI 3 - to SbI 3 -like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments. Introduction Sb x Bi 1- x I 3 alloys have very large band-gap energies and are therefore very promising materials for development as room temperature gamma-ray detectors and non-linear applications. But so far very little is actually known about the physical properties of BiI 3 and SbI 3 and even less about Sb x Bi 1- x I 3 [1,2]. These materials have hexagonal structures, similar to PbI

Optical properties of donor-triad cluster in GaAs and GaN

The effect of the transition energy of three-donor clusters on far infrared absorption in n-type semiconductor materials has been investigated by a multiconfigurational self-consistent-field model calculation and applied to GaAs and GaN systems. We show that it is crucial to consider the many-particle correlation effects within three-donor clusters. With electron correlation taken into account, the present results support the interpretation of a very recent unidentified peak energy observed in absorption measurement of GaN as due to electronic transitions in these clusters. We also corroborate the suggestion that the X line in GaAs arises from such transitions.

Electronic and Optical Properties of TiO2

The electronic and optical properties of the rutile titanium dioxide compound have been investigated experimentally by absorption measurements and theoretically by a full‐potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA). The thin films for the absorption measurements were prepared by DC magnetron sputtering. The theoretical results for the absorption compared qualitatively well with the experimental findings. The dielectric functions and band‐structure have also been calculated, and the LDA band‐gap energy is corrected by an on‐site Coulomb potential.

Spectroscopy studies of 4H-SiC

Calculations of the total dielectric functions and the optical bandgap energy (OBGE) of 4HSiC were performed by the full-potential linear muffin-tin-orbital method. The results are compared to spectroscopic ellipsometry dielectric measurements agreeing closely over in a wide range of energies. The obtained theoretical value of the (OBGE) agrees very closely with the measured ones obtained by transmission and photoacoustic spectroscopies at room temperature performed on 470 µm thick wafer and a 25 µm thick homoepitaxial layer of 4H-SiC samples grown (n-type, Siface) by hot wall CVD.

Electrical field effects in n-type MOSFET and metal–nonmetal transition

Abstract The effects of disorder, correlation, external electric field, impurity concentration, and impurity location near and at the Si/SiO 2 interface of a metal-oxide semiconductor field effect transistor (MOSFET), have been investigated. The binding and correlation energies are strongly dependent on the electric field and impurity location. The Hubbard–Mott like model provides further evidence of a MNM transition in agreement with recent experimental findings.