Person: Díaz-Guerra Viejo, Carlos
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First Name
Carlos
Last Name
Díaz-Guerra Viejo
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
Identifiers
5 results
Search Results
Now showing 1 - 5 of 5
Item Defect assessment of Mg-doped GaN by beam injection techniques(Journal of Applied Physics, 2003) Díaz-Guerra Viejo, Carlos; Piqueras De Noriega, Francisco 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.Item Time-resolved cathodoluminescence assessment of deep-level transitions in hydride-vapor-phase-epitaxy GaN(Applied Physics Letters, 2003) Díaz-Guerra Viejo, Carlos; Piqueras De Noriega, Francisco Javier; Cavallini, A.The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 mus, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of mus were measured at 87 K for all the deep-level emissions found in the layers.Item Electrical and optical characterization of GaN HVPE layers related to extended defects(Journal of Physics-Condensed Matter, 2002) Castaldini, A.; Cavallini, A.; Polenta, L.; Díaz-Guerra Viejo, Carlos; Piqueras De Noriega, Francisco JavierThe study of the effect of extended defects, present in very large numbers in GaN epilayers, on the material properties and device performance is one of the most important aims of the current research in the field of III nitrides. Thickness strongly influences electrical and optical properties of epitaxially grown GaN. Due to the lattice mismatch between sapphire and GaN, extended defects (mainly threading dislocations) are generated at the sapphire/epilayer interface, and a degenerate layer, characterized by high defect density and high conductivity. has been observed. Movin toward the top surface, the density of the extended defects, which seem to greatly affect the material properties. gradually decreases. This fact mainly causes the commonly observed electrical and optical inhomogeneities. This work deals with the comparative study by means of optical and electrical characterization between two HVPE-grown layers with different thickness (2.6 and 55 mum) in order to check the effects of the extended defect distribution across the sample.Item Characterization of thin layers of n- and p-type GaN(Materials Science and Engineering B-Solid State Materials for Advanced Technology, 2002) Castaldini, A.; Cavallini, A.; Polenta, L.; Díaz-Guerra Viejo, Carlos; Piqueras De Noriega, Francisco JavierTechnological improvement of GaN-based devices for electronic and optoelectronic applications makes essential both monitoring and controlling point and extended defects, which can have detrimental effects in device performance. For gallium nitride, thickness is a key parameter controlling the density and distribution of defects, especially extended ones. In this work highly defective thin GaN layers, both p- and n-type, have been characterized by photocurrent (PC) and time-resolved cathodoluminescence (TRCL) spectroscopy in order to evidence the presence of defect-related bands influencing the electrical and optical activity of the material. Scanning microscopy-based techniques, namely electron beam induced current (EBIC), CL imaging and optical beam induced current (OBIC) have been applied to investigate the recombination activity and the spatial distribution of the extended defects.Item Time-resolved cathodoluminescence and photocurrent study of the yellow band in Si-doped GaN(Journal of Applied Physics, 2003) Díaz-Guerra Viejo, Carlos; Piqueras De Noriega, Francisco Javier; Castaldini, A.; Cavallini, A.; Polenta, L.Time-resolved cathodoluminescence (TRCL) and photocurrent (PC) spectroscopies have been applied to the study of the yellow band of Si-doped GaN. Measurements carried out combining both techniques unambiguously reveal the complex nature of this broad emission and confirm that different deep defect levels are involved in the observed luminescence. Five emission bands centered at 1.89, 2.03, 2.16, 2.29, and 2.38 eV were found by steady state and time-resolved CL investigations, while PC spectra showed four transitions at about 2.01, 2.14, 2.28, and 2.43 eV. The behavior of the deep-level emissions intensity as a function of the excitation pulse width as well as their decay times were investigated by TRCL. A decay time of 245 mus was measured for the 2.29 eV emission band, while longer decay times of 315 and 340 mus were found, respectively, for the 2.16 and 2.38 eV bands, in agreement with TRCL spectra. The appearance of the 2.03, 2.16, 2.29 eV and 2.38-2.43 eV peaks both in PC and CL spectra suggests that these bands are related to deep acceptor to band transitions, as supported by the single exponential character of the corresponding decay transients.