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11 results on '"Cheze C."'

1. Luminescent N-polar (In,Ga)N/GaN quantum wells grown by plasma-assisted molecular beam epitaxy at high temperature

Author

Chèze, C., Feix, F., Lähnemann, J., Flissikowski, T., Brandt, O., Kryśko, M., Wolny, P., Turski, H., and Skierbiszewski, C.

Subjects
Condensed Matter - Materials Science, 00A79, 74A35
Abstract

N-polar (In,Ga)N/GaN quantum wells prepared on freestanding GaN substrates by plasma-assisted molecular beam epitaxy at conventional growth temperatures of about 650 {\deg}C do not exhibit any detectable luminescence even at 10 K. In the present work, we investigate (In,Ga)N/GaN quantum wells grown on Ga- and N-polar GaN substrates at a constant temperature of 730 {\deg}C. This exceptionally high temperature results in a vanishing In incorporation for the Ga-polar sample. In contrast, quantum wells with an In content of 20% and abrupt interfaces are formed on N-polar GaN. Moreover, these quantum wells exhibit a spatially homogeneous green luminescence band up to room temperature, but the intensity of this band is observed to strongly quench with temperature. Temperature-dependent photoluminescence transients show that this thermal quenching is related to a high density of nonradiative Shockley-Read-Hall centers with large capture coefficients for electrons and holes., Comment: 10 pages, 2 figures, 1 table

Published
2017
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2. In/GaN(0001)-$\boldsymbol{{\mathsf{\left(\!\sqrt{3}\times\!\sqrt{3}\right)\!R30^{\circ}}}}$ adsorbate structure as a template for embedded (In,Ga)N/GaN monolayers and short-period superlattices

Author

Chèze, C., Feix, F., Anikeeva, M., Schulz, T., Albrecht, M., Riechert, H., Brandt, O., and Calarco, R.

Subjects
Condensed Matter - Materials Science
Abstract

We explore an alternative way to fabricate (In,Ga)N/GaN short-period superlattices on GaN(0001) by plasma-assisted molecular beam epitaxy. We exploit the existence of an In adsorbate structure manifesting itself by a $(\sqrt{3}\times\!\sqrt{3})\text{R}30^{\circ}$ surface reconstruction observed in-situ by reflection high-energy electron diffraction. This In adlayer accommodates a maximum of 1/3 monolayer of In on the GaN surface and, under suitable conditions, can be embedded into GaN to form an In$_{0.33}$Ga$_{0.67}$N quantum sheet whose width is naturally limited to a single monolayer. Periodically inserting these quantum sheets, we synthesize (In,Ga)N/GaN short-period superlattices with abrupt interfaces and high periodicity as demonstrated by x-ray diffractometry and scanning transmission electron microscopy. The embedded quantum sheets are found to consist of single monolayers with an In content of 0.25-0.29. For a barrier thickness of 6 monolayers, the superlattice gives rise to a photoluminescence band at 3.16 eV, close to the theoretically predicted values for these structures., Comment: 9 pages, 2 figures Submitted to Appl. Phys. Lett

Published
2017
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3. Interface Formation during the Growth of Phase Change Material Heterostructures Based on Ge-Rich Ge-Sb-Te Alloys

Author

Cheze, C, Riva, F, Di Bella, G, Placidi, E, Prili, S, Bertelli, M, Fattorini, A, Longo, M, Calarco, R, Bernasconi, M, Abou El Kheir, O, Arciprete, F, Cheze C., Riva F. R., Di Bella G., Placidi E., Prili S., Bertelli M., Fattorini A. D., Longo M., Calarco R., Bernasconi M., Abou El Kheir O., Arciprete F., Cheze, C, Riva, F, Di Bella, G, Placidi, E, Prili, S, Bertelli, M, Fattorini, A, Longo, M, Calarco, R, Bernasconi, M, Abou El Kheir, O, Arciprete, F, Cheze C., Riva F. R., Di Bella G., Placidi E., Prili S., Bertelli M., Fattorini A. D., Longo M., Calarco R., Bernasconi M., Abou El Kheir O., and Arciprete F.

Abstract

In this study, we present a full characterization of the electronic properties of phase change material (PCM) double-layered heterostructures deposited on silicon substrates. Thin films of amorphous Ge-rich Ge-Sb-Te (GGST) alloys were grown by physical vapor deposition on Sb2 Te3 and on Ge2 Sb2 Te5 layers. The two heterostructures were characterized in situ by X-ray and ultraviolet photoemission spectroscopies (XPS and UPS) during the formation of the interface between the first and the second layer (top GGST film). The evolution of the composition across the heterostructure interface and information on interdiffusion were obtained. We found that, for both cases, the final composition of the GGST layer was close to Ge2 SbTe2 (GST212), which is a thermodynamically favorable off-stoichiometry GeSbTe alloy in the Sb-GeTe pseudobinary of the ternary phase diagram. Density functional theory calculations allowed us to calculate the density of states for the valence band of the amorphous phase of GST212, which was in good agreement with the experimental valence bands measured in situ by UPS. The same heterostructures were characterized by X-ray diffraction as a function of the annealing temperature. Differences in the crystallization process are discussed on the basis of the photoemission results.

Published
2022

4. Cathodoluminescence of Ga_(1-x)In_xAs_ySb_(1-y) epitaxial layers

Author

Cheze, C., Méndez Martín, Bianchi, Piqueras de Noriega, Javier, Corregidor, V., Cheze, C., Méndez Martín, Bianchi, Piqueras de Noriega, Javier, and Corregidor, V.

Abstract

Corresponding author: piqueras@fis.ucm.es. This work was carried out in the frame of the European network HPRN-CT-2001-00199. Partial support of MEC (MAT2003-00455) is acknowledged. The samples were grown in the Fraunhofer Institute ISE in Freiburg. The collaboration of N. P. Barradas and M. Reis, Quaternary Ga_(1-x)In_xAs_ySb_(1-y) layers lattice matched to a GaSb substrate are of interest for applications in the infrared range. In this work, the luminescence of Ga_(1-x)In_xAs_ySb_(1-y) layers grown on GaSb by metal organic vapor phase epitaxy (MOVPE) with different In and As contents, has been studied by cathodoluminescence (CL) in a scanning electron microscope (SEM). CL images show a cellular structure which indicates the presence of dislocations decorated by recombination centers. Band gap values of 0.735 eV and 0.717 eV were measured from the CL spectra of two samples with diferent In content. This result is analyzed in the frame of existing theoretical models relating band gap with In and As content, in quaternary lattice matched layers. The band gap values are in good agreement with results of atomistic pseudopotential calculations., MEC, European network, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Published
2023

6. J Ethnopharmacol

Author

HAMZA, N., BERKE, B., UMAR, A., CHEZE, C., GIN, H., and MOORE, Nicholas

Published
2019

7. Cathodoluminescence of Ga_(1-x)In_xAs_ySb_(1-y) epitaxial layers

Author

Cheze, C., Méndez Martín, Bianchi, Piqueras de Noriega, Javier, and Corregidor, V.

Subjects
Física de materiales
Abstract

Quaternary Ga_(1-x)In_xAs_ySb_(1-y) layers lattice matched to a GaSb substrate are of interest for applications in the infrared range. In this work, the luminescence of Ga_(1-x)In_xAs_ySb_(1-y) layers grown on GaSb by metal organic vapor phase epitaxy (MOVPE) with different In and As contents, has been studied by cathodoluminescence (CL) in a scanning electron microscope (SEM). CL images show a cellular structure which indicates the presence of dislocations decorated by recombination centers. Band gap values of 0.735 eV and 0.717 eV were measured from the CL spectra of two samples with diferent In content. This result is analyzed in the frame of existing theoretical models relating band gap with In and As content, in quaternary lattice matched layers. The band gap values are in good agreement with results of atomistic pseudopotential calculations.

Published
2006

10. Waveguide Design for Long Wavelength InGaN Based Laser Diodes.

Author

MUZIOŻ, G., TURSKI, H., SIEKACZ, M., SAWICKA, M., WOLNY, P., CHEZE, C., CYWIŃSKI, G., PERLIN, P., and SKIERBISZEWSKI, C.

Subjects
WAVEGUIDES, VACUUM tubes, MOLECULAR beams, MOLECULAR beam epitaxy, CRYSTAL growth
Abstract

One-dimensional optical waveguide calculations were performed to study the dependence of waveguide design on confinement factor (Γ) and optical losses (αi) of nitride laser diodes for emission wavelength ranging from 405 nm to 520 nm. We found that the conventional waveguide design containing GaN waveguide and AlGaN cladding layers known from violet laser diode does not support sufficient confinement of the optical mode for long wavelength devices (λ > 450 nm). We proposed a new design consisting of a thick InGaN waveguide which enhances the confinement. We compared the theoretical predictions with laser diodes grown by plasma assisted molecular beam epitaxy. [ABSTRACT FROM AUTHOR]

Published
2012

11. Interface Formation during the Growth of Phase Change Material Heterostructures Based on Ge-Rich Ge-Sb-Te Alloys

Author

Caroline Chèze, Flavia Righi Riva, Giulia Di Bella, Ernesto Placidi, Simone Prili, Marco Bertelli, Adriano Diaz Fattorini, Massimo Longo, Raffaella Calarco, Marco Bernasconi, Omar Abou El Kheir, Fabrizio Arciprete, Cheze, C, Riva, F, Di Bella, G, Placidi, E, Prili, S, Bertelli, M, Fattorini, A, Longo, M, Calarco, R, Bernasconi, M, Abou El Kheir, O, and Arciprete, F

Subjects
Settore FIS/03, General Chemical Engineering, Ge-rich Ge-Sb-Te alloy, Electronic propertie, Condensed Matter::Materials Science, Electronic properties, Ge-rich Ge-Sb-Te alloys, Heterostructures, PCM, heterostructures, electronic properties, Heterostructure, General Materials Science, FIS/03 - FISICA DELLA MATERIA
Abstract

In this study, we present a full characterization of the electronic properties of phase change material (PCM) double-layered heterostructures deposited on silicon substrates. Thin films of amorphous Ge-rich Ge-Sb-Te (GGST) alloys were grown by physical vapor deposition on Sb2Te3 and on Ge2Sb2Te5 layers. The two heterostructures were characterized in situ by X-ray and ultraviolet photoemission spectroscopies (XPS and UPS) during the formation of the interface between the first and the second layer (top GGST film). The evolution of the composition across the heterostructure interface and information on interdiffusion were obtained. We found that, for both cases, the final composition of the GGST layer was close to Ge2SbTe2 (GST212), which is a thermodynamically favorable off-stoichiometry GeSbTe alloy in the Sb-GeTe pseudobinary of the ternary phase diagram. Density functional theory calculations allowed us to calculate the density of states for the valence band of the amorphous phase of GST212, which was in good agreement with the experimental valence bands measured in situ by UPS. The same heterostructures were characterized by X-ray diffraction as a function of the annealing temperature. Differences in the crystallization process are discussed on the basis of the photoemission results.

Published
2022

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