Person:
Díaz-Guerra Viejo, Carlos

First Name

Carlos

Last Name

Díaz-Guerra Viejo

URI

https://hdl.handle.net/20.500.14352/75094

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Física Aplicada

Identifiers

Full item page

Search Results

Now showing 1 - 10 of 36

Defect assessment of Mg-doped GaN by beam injection techniques
(Journal of Applied Physics, 2003) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Castaldini, A.; Cavallini, A.; Polent, L.
The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65-2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep donors are involved in the mechanism responsible for the 3.01 eV emission.
Technical developments and principal results of vertical feeding method for GaSb and GaInSb alloys
(Thermophotovoltaic Generation of Electricity, Thermophotovoltaic Generation of Electricity, 2007) Vincent López, José Luis; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Dieguez, E.
In this work, the experimental set-up of the Vertical Feeding Method (VFM) which has been used for the preparation of GaSb and GaInSb materials is presented. The different elements of the set-up are detailed as well as the preparation process. The different configurations that have been used for material production are briefly described and the principal results are summarized. In the case of Te-doped GaSb materials, the study, focused on the grain size and structure of the as-grown materials, showed that single crystals can be obtained with the VFM. In the case of GaInSb materials, the study, focused on the spatial indium distribution in the solid phase prepared with the different VFM configurations, showed that an effective band edge reduction can be achieved.
Luminescence from indented Te-doped GaSb crystals
(Semiconductor Science and Technology, 2004) Chioncel, M. F.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier
Cathodoluminescence in the scanning electron microscope has been used to investigate the effect of plastic deformation, produced by indentation, in Te-doped GaSb crystals. Deformation has been found to cause a strong quenching of the luminescence emission as well as spectral changes. In particular, the decrease of the near band edge emission is accompanied by the relative increase of the defect band A and of the 730 meV band related to the VGaGaSbTesb centres. Annealing treatments up to 600 degreesC lead to partial recovery of the deformation induced defects, and reveal the existence of Te out-diffusion processes from the deformed areas.
Cathodoluminescence microscopy and spectroscopy of n-type 4H-SiC epilayers
(European Physical Journal-Applied Physics, 2004) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier
Cathodoluminescence (CL) microscopy and spectroscopy have been used to investigate the nature and spatial distribution of defects and impurities in n-type epitaxial 4H-SiC. CL microscopy reveals the existence of 6H-SiC polytype inclusions, while CL spectra recorded at different excitation conditions show luminescence emission related to deep levels in the SiC epilayer. Deconvolution of the mentioned spectra indicates the complex character of the deep-level CL emission, that is actually composed of four bands centred near 2.72, 2.56, 2.42 and 2.00 eV at 88 K. The origin of these bands is discussed considering previous deep level transient spectroscopy measurements carried out in the same material investigated in the present work.
Structural and cathodoluminescence study of mechanically milled silicon
(Semiconductor Science and Technology, 2002) Díaz-Guerra Viejo, Carlos; Montone, A.; Piqueras de Noriega, Javier; Cardellini, F.
The structural and luminescent properties of nanocrystalline silicon produced by high-energy ball milling of Si single crystals have been investigated using transmission electron microscopy (TEM), x-ray diffraction (XRD) and cathodoluminescence (CL) in a scanning electron microscope. XRD measurements show that the average size of the nanocrystals in the milled samples is about 30 nm but TEM reveals a wide range of size distribution including crystallites with the dimension of few nanometres. Ball milling causes the appearance of a visible luminescence band at 1.61 eV, attributed to the presence of nanocrystals, and a near-infrared band peaked at about 0.79 eV which is suggested to be related to the high density of extended defects formed during the mechanical treatment. These bands, attributed to processes in Si, are not observed in the cathodoluminescent spectra of untreated and ball-milled SiO2 powder.
Cathodoluminescence study of InxGa1_xSb crystals grown by the Bridgman method
(Journal of Crystal Growth, 2004) Chioncel, M. F.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Vincent, J.; Bermúdez, V.; Diéguez, E.
The nature and the spatial distribution of radiative defects in InxGa1-xSb grown by the vertical Bridgman method have been studied by cathodoluminescence (CL) in a scanning electron microscope. The CL results have been complemented by X-ray microanalysis and backscattered electron imaging to relate the local luminescence properties to the chemical composition. Measurements of the band-gap energy from the CL spectra, supported by X-ray compositional mappings, reveal an effective incorporation of In in the matrix, leading to the formation of the ternary alloy in the whole volume of the ingot. A low gradient of the In content along the growth axis has been found. The CL spectra of the ternary alloy exhibit similar general features to those reported for GaSb. An observed red shift of the near band edge luminescence in InxGa1-xSbx relative to that of GaSb, is due to the reduction in the band gap with increasing x. A band often observed in the CL spectra, peaked at about 20 meV below the band-gap energy, is attributed to the presence in the ternary alloy of an acceptor level that would correspond to the V-Ga-Ga-Sb acceptor in GaSb.
Cathodoluminescence mapping and spectroscopy of Te-doped In_xGa_(1-x)Sb grown by the vertical Bridgman method under an alternating magnetic field
(Superlattices and Microstructures, 2009) Díaz-Guerra Viejo, Carlos; Mitric, A.; Piqueras de Noriega, Javier; Duffar, T.
Cathodoluminescence (CL) in the scanning electron microscope and wavelength dispersive X-ray microanalysis (WDX) have been used to assess the homogeneity of a whole Te-doped In_xGa_(1-x)Sb ingot grown by the vertical Bridgman method under an alternating magnetic field. In particular, WDX has been used to determine the chemical composition of the ingot along the growth axis and several radial directions, while CL has been used to investigate the effective incorporation of In into the alloy, the nature and distribution of extended defects influencing the luminescence of the material and the shape evolution of the growth interfaces along the growth axis. CL spectroscopy reveals that doping with Te influences the band gap energy of this ternary compound through the Moss-Burstein effect.
Cathodoluminescence study of the radiative recombination properties of Se-doped GaSb crystals
(Journal of Applied Physics, 2005) Díaz-Guerra Viejo, Carlos; Vincent, J.; Piqueras de Noriega, Javier; Bermudez, V.; Diéguez, E.
The radiative recombination properties of Se-doped GaSb crystals grown by the Bridgman method have been investigated by cathodoluminescence (CL) microscopy and spectroscopy in the scanning electron microscope. A CL band centered at about 765 meV, not previously observed in undoped GaSb, is generally the dominant emission. CL spectra recorded under different excitation conditions suggest that this band can be attributed to a Se-related level-to-band transition. The spatial distribution of the 765 meV emission, as observed in the CL images, indicates an inhomogeneous Se distribution in the material.
Structural, magnetic and luminescent characteristics of Pr3+-doped ZrO2 powders synthesized by a sol–gel method
(Journal of Physics D: Applied physics, 2009) Isasi Marín, Josefa; Pérez Estébanez, Marta; Díaz-Guerra Viejo, Carlos; Fernández Castillo, Jesús; Correcher, Virgilio; Cuervo Rodríguez, María Rocío
The structural, magnetic and luminescence properties of praseodymium-doped zirconia powders of compositions Pr0.03Zr0.97O2 and Pr0.05Zr0.95O2 synthesized by a sol–gel process have been investigated. X-ray diffraction patterns indicate that these materials crystallize in a tetragonal fluorite-type structure. Scanning electron microscopy shows that the powders exhibit an agglomerated microcrystalline structure and the grain size may be in the order of 5–20μm. The study of the magnetic properties of these doped metal oxides indicates a Curie–Weiss behaviour in the temperature range (100–300)K that allow us to estimate an effective magnetic moment of 3.51μB, which indicates the presence of Pr3+ in the grown samples. Cathodoluminescence spectra recorded at temperatures between 85 and 295K show emission peaks that can be attributed to transitions between different states within the 4f2 configuration of Pr3+ ions incorporated in the zirconia crystal lattice. Thermoluminescence measured at temperatures ranging from 373 to 773K and at 550 nm wavelength show an intense and broad peak around 653K for the Pr-doped zirconia which is not observed in the undoped material.
Magnetic transitions in alpha-Fe_2O_3 nanowires
(Journal of Applied Physics, 2009) Díaz-Guerra Viejo, Carlos; Pérez García, Lucas; Piqueras de Noriega, Javier; Chioncel, M. F.
Magnetic transitions in single-crystal alpha-F_2O_3 (hematite) nanowires, grown by thermal oxidation of iron powder, have been studied in the range of 5-1023 K with a superconducting quantum interference device below room temperature and with a vibrating sample magnetometer at higher temperatures. The broad temperature range covered enables us to compare magnetic transitions in the nanowires with the transitions reported for bulk hematite. Morin temperatures (T-M) of the nanowires and of hematite bulk reference powder were found to be 123 and 263 K, respectively. Also the Neel temperature (T-N) of the nanowires, 852 K, was lower than the bulk T-N value. Measurements of the magnetization as a function of temperature show an enhanced signal in the nanowires, which suggests a decrease in the anti ferromagnetic coupling. A coercive field observed below T-M in the hysteresis loops of the nanowires is tentatively explained by the presence of a magnetic phase.