Search

Your search keyword '"Fernandez, J. R. L."' showing total 17 results
Start Over Author "Fernandez, J. R. L."
17 results on '"Fernandez, J. R. L."'

3. Hole mobility in zincblende c–GaN.

Author

Rodrigues, C. G., Fernandez, J. R. L., Leite, J. R., Chitta, V. A., Freire, V. N., Vasconcellos, A. R., and Luzzi, R.

Subjects
*THERMODYNAMICS, *NITRIDES, *ELECTRIC fields, *HOLES (Electron deficiencies), *SEMICONDUCTORS, *SCATTERING (Physics)
Abstract

We consider the nonequilibrium thermodynamic state of carriers in III-nitrides, and calculate the mobility of holes in cubic GaN layers under electric fields of low intensity. The contribution of different scattering mechanisms to the mobility is analyzed, and the relevance of each one is characterized. Satisfactory agreement with recently published experimental data is obtained.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

4. Structural and vibrational properties of molecular beam epitaxy grown cubic (Al, Ga)N/GaN heterostructures.

Author

Frey, T., As, D. J., Bartels, M., Pawlis, A., Lischka, K., Tabata, A., Fernandez, J. R. L., Silva, M. T. O., Leite, J. R., Haug, C., and Brenn, R.

Subjects
MOLECULAR beam epitaxy, GALLIUM nitride, HETEROSTRUCTURES
Abstract

The radio-frequency plasma-assisted molecular beam epitaxy of cubic Al[sub y]Ga[sub 1-y]N/GaN heterostructures on GaAs(001) substrates is reported. Rutherford backscattering spectroscopy, high resolution x-ray diffraction, and first-order micro-Raman spectroscopy measurements were used to characterize the structural and vibrational properties of the alloy epilayers. The Al content of the alloy is in the range from 0.07

Published
2001
Full Text
View/download PDF

5. Raman study of collective plasmon-longitudinal optical phonon excitations in cubic GaN and Al[sub x]Ga[sub 1-x]N epitaxial layers.

Author

Pusep, Yu. A., Silva, M. T. O., Fernandez, J. R. L., Chitta, V. A., Leite, J. R., Frey, T., As, D. J., Schikora, D., and Lischka, K.

Subjects
PLASMONS (Physics), EXCITON theory
Abstract

The plasmon-longitudinal optical (LO) phonon collective excitations were studied by Raman scattering in cubic GaN doped with Si and in intrinsically doped cubic Al[sub x]Ga[sub 1-x]N alloys. The specific asymmetry of the corresponding Raman lines, associated with the dispersion of the coupled excitations was clearly detected in GaN. The spatial coherence of the relevant coupled oscillations was determined from the comparison of the experimental Raman spectra with the calculated ones. A broad line, which was previously attributed to the overdamped plasmon-LO phonon oscillations, was also observed in the GaN and Al[sub x]Ga[sub 1-x]N samples in the range between the transversal optical and LO phonon frequencies. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2002
Full Text
View/download PDF

7. Microelectronics Journal

Author

Araújo, Carlos Moysés, Fernandez, J. R. L., Silva, A. Ferreira da, Pepe, Iuri Muniz, Leite, J. R., Sernelius, Bo E., Persson, C., and As, D. J.

Subjects
Resistivity, Band-gap shift, Metal–nonmetal transition, Photoluminescence
Abstract

Texto completo: acesso restrito. p. 365–369 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2012-12-14T13:05:19Z No. of bitstreams: 1 1-s2.0-S0026269201001331-main.pdf: 155864 bytes, checksum: 8a865844ea6f316271efb8e9d061d801 (MD5) Made available in DSpace on 2012-12-14T13:05:19Z (GMT). No. of bitstreams: 1 1-s2.0-S0026269201001331-main.pdf: 155864 bytes, checksum: 8a865844ea6f316271efb8e9d061d801 (MD5) Previous issue date: 2002-04 The electrical resistivity of the Si-donor cubic GaN is investigated theoretically at low temperature. The critical impurity concentration, Nc, for the metal–nonmetal transition is estimated in three different ways: from using the generalized Drude approach (GDA) for the resistivity; from the vanishing of the chemical potential calculated using the dielectric function model with a Lorentz-Lorenz correction; from finding the crossing point between the energy in the insulating and metallic states. The bandgap narrowing (BGN) has been determined theoretically and experimentally above the MNM transition. The experimental data have been obtained with photoluminescence measurements. Theoretical and experimental results are in rough agreement in the range of impurity concentration of interest.

Published
2002
Full Text
View/download PDF

8. Journal of Crystal Growth

Author

Fernandez, J. R. L., Araújo, Carlos Moysés, Silva, A. Ferreira da, Leite, J. R., Sernelius, Bo E., and Pepe, Iuri Muniz

Subjects
B1. Nitrides, A3. Molecular beam epitaxy, A1. Doping, A1. Characterization
Abstract

Texto completo: acesso restrito. p. 420–427 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2012-12-19T16:08:03Z No. of bitstreams: 1 texto persson 1.pdf: 214916 bytes, checksum: 041422e15b6496c1ad89170febe7e407 (MD5) Made available in DSpace on 2012-12-19T16:08:03Z (GMT). No. of bitstreams: 1 texto persson 1.pdf: 214916 bytes, checksum: 041422e15b6496c1ad89170febe7e407 (MD5) Previous issue date: 2001 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 donor binding energy and the crossing point between the energies in the metallic and insulating phases. A dielectric function model with a Lorentz–Lorenz correction is used for the insulating phase. The InN presents an order of magnitude increase in Nc as compared to the other two systems. The electrical resistivity of the Si-donor system GaN is investigated theoretically and experimentally from room temperature down to 10 K. It presents a metallic character above a certain high impurity concentration identified as Nc. The samples were grown by plasma assisted molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. The model calculation is carried out from a recently proposed generalized Drude approach (GDA) presenting a very good estimation for the metallic region. The band-gap shift (BGS) of Si-doped GaN has also been investigated above the MNM transition where this shift is observed. Theoretical and experimental results have a rough agreement in a range of impurity concentration of interest.

Published
2001
Full Text
View/download PDF

9. Electrical resistivity, MNM transition and band-gap narrowing of cubic GaN : Si

Author

Araujo, C. M., Fernandez, J. R. L., da Silva, A. F., Pepe, I., Leite, J. R., Sernelius, B. E., Tabata, A., Persson, Clas, Ahuja, R., As, D. J., Schikora, D., Lischka, K., Araujo, C. M., Fernandez, J. R. L., da Silva, A. F., Pepe, I., Leite, J. R., Sernelius, B. E., Tabata, A., Persson, Clas, Ahuja, R., As, D. J., Schikora, D., and Lischka, K.

Abstract

The electrical resistivity of the Si-donor cubic GaN is investigated theoretically at low temperature. The critical impurity concentration, N-c, for the metal-nonmetal transition is estimated in three different ways: from using the generalized Drude approach (GDA) for the resistivity; from the vanishing of the chemical potential calculated using the dielectric function model with a Lorentz-Lorenz correction; from finding the crossing point between the energy in the insulating and metallic states. The bandgap narrowing (BGN) has been determined theoretically and experimentally above the MNM transition, The experimental data have been obtained with photoluminescence measurements. Theoretical and experimental results are in rough agreement in the range of impurity concentration of interest., QC 20100525

Published
2002
Full Text
View/download PDF

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

Author

Fernandez, J. R. L., Araujo, C. M., da Silva, A. F., Leite, J. R., Sernelius, B. E., Tabata, A., Abramof, E., Chitta, V. A., Persson, Clas, Ahuja, R., Pepe, I., As, D. J., Frey, T., Schikora, D., Lischka, K., Fernandez, J. R. L., Araujo, C. M., da Silva, A. F., Leite, J. R., Sernelius, B. E., Tabata, A., Abramof, E., Chitta, V. A., Persson, Clas, Ahuja, R., Pepe, I., As, D. J., Frey, T., Schikora, D., and Lischka, K.

Abstract

The critical impurity concentration N-c of the metal-nonmetal (MNM) transition for the cubic GaN, InN and AIN systems. is calculated using the following two different criteria: vanishing of the donor binding energy and the crossing point between the energies in the metallic and insulating phases. A dielectric function model with a Lorentz-Lorenz correction is used for the insulating phase. The InN presents an order of magnitude increase in N-c as compared to the other two systems. The electrical resistivity of the Si-donor system GaN is investigated theoretically and experimentally from room temperature down to 10K. It presents a metallic character above a certain high impurity concentration identified as N-c. The samples were grown by plasma assisted molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. The model calculation is carried out from a recently proposed generalized Drude approach (GDA) presenting a very good estimation for the metallic region. The band-gap shift (BGS) of Si-doped GaN has also been investigated above the MNM transition where this shift is observed. Theoretical and experimental results have a rough agreement in a range of impurity concentration of interest., QC 20100525

Published
2001
Full Text
View/download PDF

11. Optical absorption and electronic band structure first-principles calculations ofα-glycine crystals

Author

Flores, M. Z. S., primary, Freire, V. N., additional, dos Santos, R. P., additional, Farias, G. A., additional, Caetano, E. W. S., additional, de Oliveira, M. C. F., additional, Fernandez, J. R. L., additional, Scolfaro, L. M. R., additional, Bezerra, M. J. B., additional, Oliveira, T. M., additional, Bezerra, G. A., additional, Cavada, B. S., additional, and Leite Alves, H. W., additional

Published
2008
Full Text
View/download PDF

15. Surface-Coated CdS Nanocrystals.

Author

FERNANDEZ, J. R. L., DE SOUZA-PARISE, M., and MORAIS, P. C.

Subjects
*NANOCRYSTALS, *ETHYLENE glycol, *X-ray diffraction, *RAMAN spectroscopy, *PHOTOLUMINESCENCE, *SPHALERITE, *SURFACE coatings
Abstract

CdS nanocrystals were prepared using a standard colloidal route (co-precipitation chemical reaction) whereas modulation of the optical and structural properties was realized via surface coating the nanocrystals with ethylene glycol molecules using an in situ procedure. The as-produced nanocrystals were characterized by X-ray diffraction, Raman spectroscopy, UV-absorption measurements and photoluminescence. The nanocrystal quality was revealed by the spectroscopic data, though the final product presents a mixture of both zinc blende (cubic) and wurtzite (hexagonal) phases. The X-ray data indicated that the concentration of the ethylene glycol used during the synthesis process modulates the nanocrystal size and the crystal phase of the end material. [ABSTRACT FROM AUTHOR]

Published
2013
Full Text
View/download PDF

16. Room temperature ferromagnetism in cubic GaN epilayers implanted with Mn+ ions.

Author

Chitta, V. A., Coaquira, J. A. H., Fernandez, J. R. L., Duarte, C. A., Leite, J. R., Schikora, D., As, D. J., Lischka, K., and Abramof, E.

Subjects
GALLIUM nitride, MANGANESE, IONS, MOLECULAR dynamics, ELECTROMAGNETIC induction, MAGNETISM, MOLECULAR beam epitaxy, RAMAN spectroscopy
Abstract

Mn ions were implanted in p-type cubic GaN at doses from 0.6 to 2.4×1016 cm-2 at 200 keV energy. A 200-nm-thick epitaxial layer, grown by molecular beam epitaxy on GaAs(001) substrate, is used for the Mn implantation. The Mn implanted samples were subjected to an annealing at 950 °C for 1–5 min. The structural quality of the samples was investigated by high resolution x-ray diffraction and Raman spectroscopy. The annealing procedure leads to a significant increasing of the crystalline quality of the samples. Hysteresis loops were observed for all cubic GaMnN annealed samples and ferromagnetism was detected up to room temperature. [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

17. Molecular Signature in the Photoluminescence of α-Glycine, L-Alanine and L-Asparagine Crystals: Detection, ab initio Calculations, and Bio-sensor Applications.

Author

Caetano, E. W. S., Pinheiro, J. R., Zimmer, M., Freire, V. N., Farias, G. A., Bezerra, G. A., Cavada, B. S., Fernandez, J. R. L., Leite, J. R., de Oliveira, M. C. F., Pinheiro, J. A., de Lima Filho, J. L., and Leite Alves, H. W.

Subjects
MOLECULES, PHOTOLUMINESCENCE, GLYCINE, ALANINE, ASPARAGINE, CRYSTALS, BIOSENSORS
Abstract

We present the photoluminescence spectra of α-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75–3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab initio calculations of their electronic structures allow for the assignment of the observed peaks in the visible region to lattice-related processes of exciton nature associated with polaron levels. The very thin photoluminescence peaks in the ultraviolet region are assigned to intramolecular transitions, being a signature of the weakly interacting amino acid molecules in the crystals. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2005
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results