Size-dependent recombination dynamics in ZnO nanowires

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 96, 053105 (2010) and may be found at https://doi.org/10.1063/1.3294327.A deep understanding of the recombination dynamics of ZnO nanowires (NWs) is a natural step for a precise design of on-demand nanostructures based on this material system. In this work we investigate the influence of finite-size on the recombination dynamics of the neutral bound exciton around 3.365 eV for ZnO NWs with different diameters. We demonstrate that the lifetime of this excitonic transition decreases with increasing the surface-to-volume ratio due to a surface induced recombination process. Furthermore, we have observed two broad transitions around 3.341 and 3.314 eV, which were identified as surface states by studying the dependence of their life time and intensitiy with the NWs dimensions.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Globalización: nuevas prácticas educativas

ICT resources applied to educational diversity facilitate new intervention formulas in the teaching-learning processes. The present work gathers data from a series of school on-line practices for the learning of Natural and Social Sciences, as well as data from collaborative learning experiences. Also, this work studies web potential for in-service training of teachers. On-line training overcomes many of the shortcomings and difficulties of inservice training, thanks to its easy access, management and storage of information, as well as to the possibilities it offers for synchronic and diachronic communication

Spanish children's concerns for the future

This paper reports on an international study which investigated the hopes and fears of children aged 9-11 for their personal, local and global futures, together with their understanding of key issues such as poverty, racism, the environment, health and conflict. The study indicates the extent to which children feel optimistic about the future, informed about key global issues and motivated to act for change. In this paper we hear the voices of children from Spain. Spanish children’s concerns for both the local and global future are discussed as is their desire to be informed about such issues and involved in action for change. There are implications for curriculum content and service-learning activities involving community action. Findings also indicate the importance these children place on family and relationships, which is discussed in terms of the role both parents and teachers can play in effective education for citizenship. I hope not to be alone… (girl) I’m afraid that we’ll forget our dreams… (girl

Reduction of the transverse effective charge of optical phonons in ZnO under pressure

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 96, 231906 (2010) and may be found at https://doi.org/10.1063/1.3447798."From Raman scattering on a-plane wurtzite ZnO crystals we obtained a decreasing splitting between longitudinal and transversal optical phonons with A1 and E1 symmetry as a function of hydrostatic pressure up to 5.5 GPa. Consequently, the transverse effective charge (e∗T) exhibits a strong reduction with increasing pressure, yielding 2.17–14.6×10−3 P/GPa and 2.04–13.7×10−3 P/GPa (in units of the elementary charge) for the A1 and E1 phonons, respectively. We find a clear systematic in the linear pressure coefficient of e∗T with bond polarity for the series of wide-band gap semiconductors SiC, AlN, GaN, and ZnO.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Phonon plasmon interaction in ternary group-III-nitrides

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 101, 041909 (2012) and may be found at https://doi.org/10.1063/1.4739415.Phonon-plasmon-coupling in the ternary group-III-nitrides InGaN and AlGaN is investigated experimentally and theoretically. Based on the observation of broadening and shifting of the A1(LO) mode in AlGaN upon Si-doping, a lineshape analysis was performed to determine the carrier concentration. The results obtained by this method are in excellent agreement to those from Hall measurements, confirming the validity of the employed model. Finally, neglecting phonon and plasmon damping, the Raman shift of the A1(LO) mode in dependence of the carrier concentration for AlGaN and InGaN is calculated. This enables a fast and contactless determination of carrier concentrations in the future.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Temperature dependent photoluminescence of lateral polarity junctions of metal organic chemical vapor deposition grown GaN

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 110, 093503 (2011) and may be found at https://doi.org/10.1063/1.3656987.We report on fundamental structural and optical properties of lateral polarity junctions in GaN. GaN with Ga- to N-polar junctions was grown on sapphire using an AlN buffer layer. Results from scanning electron microscopy and Raman spectroscopy measurements indicate a superior quality of the Ga-polar GaN. An extremely strong luminescence signal is observed at the inversion domain boundary (IDB). Temperature dependent micro photoluminescence measurements are used to reveal the recombination processes underlying this strong emission. At 5 K the emission mainly arises from a stripe along the inversion domain boundary with a thickness of 4-5 μm. An increase of the temperature initially leads to a narrowing to below 2 μm emission area width followed by a broadening at temperatures above 70 K. The relatively broad emission area at low temperatures is explained by a diagonal IDB. It is shown that all further changes in the emission area width are related to thermalization effects of carriers and defects attracted to the IDB. The results are successfully used to confirm a theoretical model for GaN based lateral polarity junctions. Due to the strong and pronounced emission of IDBs even at elevated temperatures, it is demonstrated that lateral polarity junctions exhibit a strong potential for future high efficiency devices.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Un nuevo modo de proceder en el aula aprendiendo mediante el ordenador

El presente estudio analiza la eficacia del aprendizaje mediante ordenador (AMO) en cuarto y quinto de EGB, aplicado en un contexto didáctico en el que se enfrenta directamente al alumno con el reto de aprender a través de su propia acción, frente a la utilización convencional de la enseñanza asistida por ordenador (CAI), concebida — habitualmente — como complemento para reforzar la enseñanza el profesor. El software empleado en este estudio es del tipo drill and practice sobre el sistema métrico decimal, pero utilizado con anterioridad a las explicaciones del profesor. Se ha utilizado un diseño pretest-postest con cinco grupos de quinto de EGB (N = 148) y tres de cuarto de EGB (N = 72). El análisis de covarianza mostró la eficacia diferencial de los tratamientos, revelándose la combinación del AMO y la clase convencional como la estrategia más efectiva respecto al aprendizaje de los alumnos. Por la peculiar utilización de los programas se pone de manifiesto la potencialidad de un enfoque de carácter más inductivo, que abre nuevas posibilidades para el desarrollo del proceso de aprendizaje en el aula, reconduciendo el rol del profesor y realzando el protagonismo del alumno en su propio aprendizaje