Person: González Díaz, Germán
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First Name
Germán
Last Name
González Díaz
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Estructura de la Materia, Física Térmica y Electrónica
Area
Electrónica
Identifiers
59 results
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Now showing 1 - 10 of 59
Item Continuous and Localized Mn Implantation of ZnO(Nanoscale research letters, 2009) González Díaz, Germán; Hernández Vélez, M.; Jensen, J.; Martínez, O.; Sanz, R.; Vázquez, M.We present results derived from continuous and localized 35 keV (55)Mn(+) ion implantations into ZnO. Localized implantations were carried out by using self-ordered alumina membranes as masks leading to ordered arrays of implanted volumes on the substrate surfaces. Defects and vacancies in the small implantation volumes of ZnO were generated due to the implantation processes besides the creation of new phases. Rapid thermal annealing was applied in the case of continuous implantation. The samples were characterized by HRSEM, GIXRD, Raman spectroscopy and RBS/C. Magnetic characterization of the samples pointed out appreciable differences among the samples obtained by the different implantation methods. This fact was mainly attributed to the different volume/surface ratios present in the implanted zones as well as to the increase of Mn atom concentrations along the grain frontiers in the nanostructured surfaces. The samples also showed a ferromagnetic transition phase at temperature value higher than room temperature.Item Comparison of Raman-scattering and Shubnikov-de Haas measurements to determine charge density in doped semiconductors(Journal of Applied Physics, 2000) González Díaz, Germán; Artús, L.; Blanco, N.; Cuscó, R.; Ibáñez, J.; Long, A.R.; Rahman, M.We have verified the accuracy of free-charge determinations from Raman scattering in doped semiconductors by comparing the results obtained from phonon-plasmon coupled-mode line-shape fits with the charge-density values extracted from the analysis of the Shubnikov-de Haas oscillations. The experiments were carried out on n-InP layers, and conduction band nonparabolicity was included both in the Lindhard-Mermin model used to fit the Raman spectra and in the Shubnikov-de Haas analysis. We find a very good agreement between Raman and magnetotransport results, which confirms the reliability of the charge-density determination from Raman-scattering measurements when the line-shape analysis is carried out using the Lindhard-Mermin model.Item The effect of substrate on high-temperature annealing of GaN epilayers: Si versus sapphire(Journal of Applied Physics, 2006) González Díaz, Germán; Artús, L.; Calleja, E.; Cuscó, R.; Iborra, E.; Jiménez, J.; Pastor, D.; Peiró, F.We have studied the effects of rapid thermal annealing at 1300 degrees C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display visible alterations with craterlike morphology scattered over the surface. The annealed GaN/Si layers were characterized by a range of experimental techniques: scanning electron microscopy, optical confocal imaging, energy dispersive x-ray microanalysis, Raman scattering, and cathodoluminescence. A substantial Si migration to the GaN epilayer was observed in the crater regions, where decomposition of GaN and formation of Si3N4 crystallites as well as metallic Ga droplets and Si nanocrystals have occurred. The average diameter of the Si nanocrystals was estimated from Raman scattering to be around 3 nm. Such annealing effects, which are not observed in GaN grown on sapphire, are a significant issue for applications of GaN grown on Si(111) substrates when subsequent high-temperature processing is required.Item Study of the electrical activation of Si+-implanted InGaAs by means of Raman scattering(Journal of Applied Physics, 2003) González Díaz, Germán; Artús, L.; Blanco, N; Cuscó, R.; Hernández, S.Raman scattering has been used to study the lattice recovery and electrical activation of Si+-implanted In0.53Ga0.47 As achieved by rapid thermal annealing. The degree of crystallinity recovery, of totally amorphized samples is studied for annealing temperatures between 300 and 875degreesC. A good degree of recovery is achieved for an annealing temperature of 600degreesC. Higher annealing temperatures are required to electrically activate the Si donors. The observed LO phonon-plasmon coupled modes allow us to monitor the electrical activation by means of Raman scattering. We find that electrical activation sets in for annealing temperatures around 700degreesC, and gradually increases up to an annealing temperature of 875degreesC. The optimal conditions for the rapid thermal annealing are found to be 875degreesC for 10 s.Item Annealing effects on the interface and insulator properties of plasma-deposited Al/SiOxNyHz/Si devices(Semiconductor Science and Technology, 2004) Prado Millán, Álvaro Del; San Andrés Serrano, Enrique; Martil De La Plaza, Ignacio; González Díaz, Germán; Kliefoth, K.; Füssel, W.We have studied and compared the effects of conventional annealing in a forming gas atmosphere (430 degreesC, 20 min) and rapid thermal annealing (RTA) in an inert Ar atmosphere (400-1000 degreesC, 30 s) on Al/SiOxNyHz/Si devices. The samples were deposited by the electron cyclotron resonance plasma method at low temperature (T = 200 degreesC). The devices were characterized by surface photovoltage measurements before applying contacts and by capacitance-voltage measurements. All the as-deposited samples containing N had positive flat-band voltage, which corresponds to negative charge in the insulator and/or in the interface states (Q(INS)). Additionally, trapping of positive charge is observed when measuring from inversion to accumulation after measuring from accumulation to inversion. This behaviour is tentatively attributed to the presence of defects related to N, such as the K centre (N-3=Siup arrow) or the N dangling bond (Si-2=Nup arrow), which may be present in a negatively charged state. For samples of SiO2 composition, with a negligible N content, Q(INS) is positive. High densities of interface states (D-it), above 10(12) eV(-1) cm(-2), are observed in the as-deposited samples. Both the annealing in a forming gas atmosphere and the RTA result in the change of the sign of Q(INS) from negative to positive and a decrease of its absolute value, as well as a decrease of D-it of about one order of magnitude. The trapping of positive charge is also greatly reduced. These improvements of the electrical properties are attributed to the passivation of defects by H present in the forming gas atmosphere or in the SiOxNyHz film itself in a non-bonded state. For RTA temperatures above 700 degreesC the properties of the devices degrade due to the release of H. The combination of RTA and annealing in a forming gas atmosphere results in the best properties.Item A comparative study of the electrical properties of TiO2 films grown by high-pressure reactive sputtering and atomic layer deposition(Semiconductor Science and Technology, 2005) Martil De La Plaza, Ignacio; González Díaz, Germán; San Andrés Serrano, EnriqueOxide-semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO2 films annealed in O-2 at temperatures ranging from 600 to 900 degrees C, and atomic layer deposited (ALD) TiO2 films grown at 225 or 275 degrees C from TiCl4 or Ti(OC2H5)(4), and annealed at 750 degrees C in O-2, has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900 degrees C in oxygen atmosphere exhibit the best characteristics, with D-it density being the lowest value measured in this work (5-6 x 10(11) cm(-2) eV(-1)), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO2 film thickness and the crystallinity, since in the films annealed at 900 degrees C rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600-800 degrees C, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700 degrees C annealed HPRS films than for 750 degrees C annealed ALD TiO2 films, whereas 800 degrees C annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.Item A comparative study of anodic tantalum pentoxide and high-pressure sputtered titanium oxide(Journal of Materials Science: Materials in Electronics, 2003) Martil De La Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro Del; San Andrés Serrano, EnriqueIn this work we present a new method to fabricate improved TiO2 films by using a high-pressure sputtering system. In order to minimize the damage induced in the substrate surface by the ion bombardment, a high chamber pressure of 100 Pa is used, which is very much higher than typical values in conventional systems. We present results obtained by Xray diffraction and FTIR spectroscopy. Moreover, we will compare the properties of the resulting TiO2-insulator-metal capacitors with those of anodic Ta2O5. Very thin films of TiO2 have been obtained with a very promising quality for future electron device fabrication.Item Bonding configuration and density of defects of SiOxHy thin films deposited by the electron cyclotron resonance plasma method(Journal of Applied Physics, 2003) Martil De La Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro Del; San Andrés Serrano, EnriqueThe composition, bonding configuration, hydrogen content, and paramagnetic defects of SiOxHy thin films were studied. Films were deposited by the electron cyclotron resonance plasma method at room temperature using SiH4 and O-2 as precursor gases. The film composition was measured by heavy ion elastic recoil detection analysis and energy dispersive x-ray spectroscopy. Suboxide films with compositions ranging from SiO2 to SiH0.38 were obtained. Infrared spectroscopy showed the presence of different Si-O and Si-H vibration modes. The usual estimation of the oxygen to silicon ratio by the wave number of the Si-O-Si stretching band was not accurate for films far from stoichiometry. These off-stoichiometric films also showed a broader Si-O-Si stretching peak than the stoichiometric ones, indicating a higher bonding disorder. The position of the Si-O-Si bending and rocking modes did not depend on the film composition. On the other hand, the peak position of the Si-H modes were found strongly dependent on the Si environment. By single-wavelength ellipsometry at lambda=632.8 nm the refractive index n was found to range between 1.45 (SiO2) and 2.04 (SiO0.06H0.36). Electron spin resonance measurements showed that stoichiometric films presented the well known E' center (.Siequivalent toO(3)) with concentrations in the 10(16)-10(17) cm(-3) range, while for Si-rich films (x<1) the Si dangling bond center (Si-DB, .Siequivalent toSi(3)) was the only detectable defect, with concentrations in the 10(18)-10(19) cm(-3) range. In near-stoichiometric films both E-' and Si-DB centers were found.Item Bonding structure and hydrogen content in silicon nitride thin films deposited by the electron cyclotron resonance plasma method(Thin Solid Films, 2004) Martil De La Plaza, Ignacio; González Díaz, Germán; Prado Millán, Álvaro Del; San Andrés Serrano, EnriqueThe bonding structure and hydrogen content of amorphous hydrogenated silicon nitride (a-SiNx:H) thin films have been investigated by infrared spectroscopy and ion beam techniques. Electron cyclotron resonance plasma enhanced chemical vapor deposition was used to produce these films under different values of gas flow ratio, deposition temperature, and microwave power. The amount of bonded hydrogen was calculated from the N-H and Si-H infrared absorption bands. An increase of the SiH4 partial pressure during deposition was found to have the same effect on the H content as an increase of the substrate temperature: both cause a decrease of the N-H bond density and an increase in the number of Si-H bonds. This is explained by a competitive process in the formation of N-H and Si-H bonds during the growth of the film, whereby Si-H bonds are favored at the expense of N-H bonds when either the SiH4 flow or the substrate temperature are increased. Such tendency to chemical order is compared with previous results in which the same behavior was induced by thermal annealing or ion beam bombardment.Item C-V, DLTS and conductance transient characterization of SiNx:H/InP interface improved by N-2 remote plasma cleaning of the InP surface(Journal of Materials Science: Materials in Electronics, 2001) Martil De La Plaza, Ignacio; González Díaz, GermánElectrical characterization of Al/SiNx:H/InP structures shows that ECR nitrogen plasma cleaning of InP surfaces gives rise to a noticeable improvement in the interface quality, whereas insulator and semiconductor bulk properties are maintained at a level sufficient to be used as the gate dielectric in MIS devices. Nitrogen plasma exposure was carried out just before the SiNx plasma deposition without vacuum breaking. To obtain interface state density and to detect deep levels in the semiconductor bulk, deep level transient spectroscopy (DLTS) measurements were carried out. We have also evaluated the insulator damage density, the so-called disorder-induced gap states (DIGS), by means of conductance transient analysis. Our results show that the plasma exposure in N-2 atmospheres is a valuable and simple surface conditioning method.