Browsing by Author "Plazaola, F."

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  • Correlation between Zn vacancies and photoluminescence emission in ZnO films
    (2006) Zubiaga, A.; Garcia, J. A.; Plazaola, F.; Tuomisto, Filip; Saarinen, K.; Zuniga Perez, J.; Munoz-Sanjose, V.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Photoluminescence and positron annihilation spectroscopy have been used to characterize and identify vacancy-type defects produced in ZnO films grown on sapphire by metal-organic chemical-vapor deposition. The photoluminescence of the samples in the near band edge region has been studied, paying particular attention to the emission at 370.5nm (3.346eV). This emission has been correlated to the concentration of Zn vacancies in the films, which has been determined by positron annihilation spectroscopy.
  • On the interplay of point defects and Cd in non-polar ZnCdO films
    (2013) Zubiaga, A.; Reurings, F.; Tuomisto, Filip; Plazaola, F.; Garcia, J. A.; Kuznetsov, A. Yu.; Egger, W.; Zuniga-Perez, J.; Munoz-Sanjose, V.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Non-polar ZnCdO films, grown over m- and r-sapphire with a Cd concentration ranging between 0.8% and 5%, have been studied by means of slow positron annihilation spectroscopy (PAS) combined with chemical depth profiling by secondary ion mass spectroscopy and Rutherford back-scattering. Vacancy clusters and Zn vacancies with concentrations up to 10exp17 cm−3 and 10exp18 cm−3, respectively, have been measured inside the films. Secondary ion mass spectroscopy results show that most Cd stays inside the ZnCdO film but the diffused atoms can penetrate up to 1.3 μm inside the ZnO buffer. PAS results give an insight to the structure of the meta-stable ZnCdO above the thermodynamical solubility limit of 2%. A correlation between the concentration of vacancy clusters and Cd has been measured. The concentration of Zn vacancies is one order of magnitude larger than in as-grown non-polar ZnO films and the vacancy cluster are, at least partly, created by the aggregation of smaller Zn vacancy related defects. The Zn vacancy related defects and the vacancy clusters accumulate around the Cd atoms as a way to release the strain induced by the substitutional CdZn in the ZnO crystal.
  • Positron annihilation lifetime spectroscopy of ZnO bulk samples
    (2007) Zubiaga, A.; Plazaola, F.; Garcia, J. A.; Tuomisto, Filip; Munoz-Sanjose, V.; Tena-Zaera, R.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In order to gain a further insight into the knowledge of point defects of ZnO, positron annihilation lifetime spectroscopy was performed on bulk samples annealed under different atmospheres. The samples were characterized at temperatures ranging from 10 to 500 K. Due to difficulties in the conventional fitting of the lifetime spectra caused by the low intensity of the defect signals, we have used an alternative method as a solution to overcome these difficulties and resolve all the lifetime components present in the spectra. Two different vacancy-type defects are identified in the samples: Zn vacancy complexes (VZn−X) and vacancy clusters consisting of up to five missing Zn-O pairs. In addition to the vacancies, we observe negative-ion-type defects, which are tentatively attributed to intrinsic defects in the Zn sublattice. The effect of the annealing on the observed defects is discussed. The concentrations of the VZn−X complexes and negative-ion-type defects are in the 0.2–2 ppm range, while the cluster concentrations are 1–2 orders of magnitude lower.
  • Positron annihilation lifetime spectroscopy of ZnO bulk samples
    (2007-08) Zubiaga, A.; Plazaola, F.; Garcia, J.A.; Tuomisto, Filip; Munoz-San Jose, V.; Tena-Zaera, R.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In order to gain a further insight into the knowledge of point defects of ZnO, positron annihilation lifetime spectroscopy was performed on bulk samples annealed under different atmospheres. The samples were characterized at temperatures ranging from 10to500K. Due to difficulties in the conventional fitting of the lifetime spectra caused by the low intensity of the defect signals, we have used an alternative method as a solution to overcome these difficulties and resolve all the lifetime components present in the spectra. Two different vacancy-type defects are identified in the samples: Zn vacancy complexes (VZn−X) and vacancy clusters consisting of up to five missing Zn-O pairs. In addition to the vacancies, we observe negative-ion-type defects, which are tentatively attributed to intrinsic defects in the Zn sublattice. The effect of the annealing on the observed defects is discussed. The concentrations of the VZn−X complexes and negative-ion-type defects are in the 0.2–2ppm range, while the cluster concentrations are 1–2 orders of magnitude lower.
  • Positron annihilation spectroscopy for the determination of thickness and defect profile in thin semiconductor layers
    (2007) Zubiaga, A.; Garcia, J. A.; Plazaola, F.; Tuomisto, Filip; Zuniga-Perez, J.; Munoz-Sanjose, V.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present a method, based on positron annihilation spectroscopy, to obtain information on the defect depth profile of layers grown over high-quality substrates. We have applied the method to the case of ZnO layers grown on sapphire, but the method can be very easily generalized to other heterostructures (homostructures) where the positron mean diffusion length is small enough. Applying the method to the ratio of W and S parameters obtained from Doppler broadening measurements, W∕S plots, it is possible to determine the thickness of the layer and the defect profile in the layer, when mainly one defect trapping positron is contributing to positron trapping at the measurement temperature. Indeed, the quality of such characterization is very important for potential technological applications of the layer.
  • Positron annihilation spectroscopy for the determination of thickness and defect profile in thin semiconductor layers
    (2007-05) Zubiaga, A.; Garcia, J.A.; Plazaola, F.; Tuomisto, F.; Zuniga-Perez, J.; Munoz-Sanjose, V.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present a method, based on positron annihilation spectroscopy, to obtain information on the defect depth profile of layers grown over high-quality substrates. We have applied the method to the case of ZnO layers grown on sapphire, but the method can be very easily generalized to other heterostructures (homostructures) where the positron mean diffusion length is small enough. Applying the method to the ratio of W and S parameters obtained from Doppler broadening measurements, W∕S plots, it is possible to determine the thickness of the layer and the defect profile in the layer, when mainly one defect trapping positron is contributing to positron trapping at the measurement temperature. Indeed, the quality of such characterization is very important for potential technological applications of the layer.
  • Radiation-induced alloy rearrangement in InxGa1− xN
    (2017-03-27) Prozheeva, V.; Makkonen, I.; Cuscó, R.; Artús, L.; Dadgar, A.; Plazaola, F.; Tuomisto, F.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The effect of radiation damage on the defect and alloy structure in InxGa1− xN thin films grown on Si substrates was studied using positron annihilation spectroscopy. Prior to the measurements, the samples were subjected to double He+ implantation at 40 and 100 keV. The results show the presence of cation vacancy-like defects in high concentrations (>1018 cm−3) already in the as-grown samples. The evolution of the annihilation characteristics after the implantation suggests strong alloy disorder rearrangement under irradiation.
  • Zinc vacancies in the heteroepitaxy of ZnO on sapphire: Influence of the substrate orientation and layer thickness
    (2005) Zubiaga, A.; Tuomisto, Filip; Plazaola, F.; Saarinen, K.; Garcia, J. A.; Rommeluere, J. F.; Zuniga-Perez, J.; Munoz-Sanjose, V.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Positron annihilation spectroscopy has been used to study the vacancy-type defects produced in films grown by metalorganic chemical vapor deposition on different sapphire orientations. Zn vacancies are the defects controlling the positron annihilation spectra at room temperature. Close to the interface (<500nm) their concentration depends on the surface plane of sapphire over which the ZnO film has been grown. The Zn vacancy content in the film decreases with thickness, and above 1μm it is independent of the substrate orientation.