Person: Cremades Rodríguez, Ana Isabel
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First Name
Ana Isabel
Last Name
Cremades Rodríguez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Area
Ciencia de los Materiales e Ingeniería Metalúrgica
Identifiers
5 results
Search Results
Now showing 1 - 5 of 5
Item Study of structural defects limiting the luminescence of InGaN single quantum wells(Materials Science and Engineering B-Solid State Materials for Advanced Technology, 2002) Cremades Rodríguez, Ana Isabel; Piqueras De Noriega, Francisco Javier; Albrecht, M.; Stutzmann, M.; Strunk, H.P.InGaN quantum well (QW) structures with different thicknesses have been characterised by means of cathodoluminescence (CL) in the scanning electron microscope and transmission electron microscopy (TEM), in order to study the structural defects that limit the device operation, Misfit dislocations appear as non-radiative centres in the CL images and compete with the quantum-well related luminescence. The luminescence red shift with increasing QW thickness has been found to be influenced by composition fluctuations.Item Effects of phase separation and decomposition on the minority carrier diffusion length in AlxGa1-xN films(Journal of Applied Physics, 2000) Cremades Rodríguez, Ana Isabel; Albrecht, M.; Krinke, J.; Dimitrov, R.; Stutzmann, M.; Strunk, H. P.Combined electron beam induced current and transmission electron microscopy (TEM) measurements have been performed on both undoped and Si-doped AlGaN epitaxial films with aluminum contents x ranging from x = 0 to x = 0.79, in order to correlate the electrical and structural properties of the films. The diffusion length of holes in the films ranges between 0.3 and 15.9 mu m, and the estimated lifetime of holes for doped samples varies between 0.2 ns and 16 mu s. Different effects contribute to the observed increase in the diffusion length with increasing aluminum content. Among others, dislocations seem to be active as nonradiative recombination sites, and phase separation and decomposition as observed by TEM in Al-rich alloys lead to the formation of a spatially indirect recombination path due to the piezoelectric field in the films. Potential fluctuations associated with these phase irregularities could also give rise to electron induced persistent conductivity contributing to the increase of the diffusion length. From our experimental observations, we conclude that the silicon dopants are partially activated in Al-rich alloys, and do not influence significantly the values of the diffusion length of holes in these samples.Item Optical properties and defect structure of MOVPE InGaN films(Optical Microestructuras Characterization of Semiconductors, Optical Microstructural Characterization of Semiconductors, 2000) Cremades Rodríguez, Ana Isabel; Albrecht, M.; Ulloa, J.M.; Piqueras De Noriega, Francisco Javier; Strunk, H.P.; Hanser, D.; Davis, R. F.A series of 100 nm thick InGaN films with In content up to 14% has been grown by MOVPE on SiC substrates. Optical characterization was carried out by means of reflectance spectrometry, photoluminescence and cathodoluminescence. Optical properties of the samples have been correlated with the microstructural properties measured by atomic force microscopy, transmission electron microscopy and X-ray diffraction data. Results indicate a dependence of the optical properties on the In content in the sample, as well as on the residual stress in the films induced by Indium incorporation. Part of the strain is reduced elastically by formation of pinholes which reach the InGaN/GaN interface, where first misfit dislocations are observed to form. Our results show that luminescence is directly correlated with the strain distribution in the layers. Pinholes are observed to act as nonradiative recombination sites for carriers, while strain relaxation around pinholes may enhance luminescence emission. We discuss the influence of strain with respect to In incorporation, the appearance of piezoelectric fields and effects due to strain induced band bending.Item Carrier recombination at screw dislocations in n-type AlGaN layers(Phisica Status Solidibi B-Basic Research, 1999) Albrecht, M.; Cremades Rodríguez, Ana Isabel; Krinke, J.; Christiansen, S.; Ambacher, O.; Piqueras De Noriega, Francisco Javier; Strunk, H. P.; Stutzmann, M.We analyse the recombination and scattering at dislocations in Si doped AlGaN layers by transmission electron microscopy (TEM), electron beam induced current (EBIC) and cathodoluminescence. We show that c-type screw dislocations are nonradiative recombination centres. From temperature dependent measurements of the EBIC contrast we find a shallow acceptor state 20 meV above the valence band. The level can be understood iri terms of one-dimensional dislocation bands split off by the dislocation deformation field. In addition piezoelectric potentials play a role.Item Minority carrier diffusion length in AlGaN: A combined electron beam induced current and transmission microscopy(Solid State Phenomena, 1998) Cremades Rodríguez, Ana Isabel; Albrecht, M.; Voigt, A.; Krinke, J.; Dimitrov, R.; Ambacher, O.; Stutzmann, M.Combined electron beam induced current and transmission electron microscopy measurements have been performed on both undoped and Si-doped AlGaN epitaxial films with aluminium contents x ranging from x=0 to x=0.79. TEM analysis shows the distribution and type of structural defects, the content of cubic phase and the decomposition phenomena strongly to depend on the Al content of the layers. The influence of the cubic phase on the electronic properties of the samples is discussed taking into account the high piezoelectric effect present in these alloys. The diffusion length of minority carriers has been determined by EBIC measurements and a lower limit of the lifetime has been estimated.