Floris Reurings
Helsinki University of Technology
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Featured researches published by Floris Reurings.
Applied Physics Letters | 2010
Gregor Koblmüller; Floris Reurings; Filip Tuomisto; James S. Speck
The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ∼780–790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth (0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N∼1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ∼1016 cm−3 for all films attribute further to the significant benefits of the high-temperature growth regime.
Applied Physics Letters | 2010
Floris Reurings; Filip Tuomisto; Chad S. Gallinat; Gregor Koblmüller; James S. Speck
The authors have applied positron annihilation spectroscopy to study the effect of different growth conditions on vacancy formation in In- and N-polar InN grown by plasma-assisted molecular beam epitaxy. The results suggest that the structural quality of the material and limited diffusion of surface adatoms during growth dictate the In vacancy formation in low electron-density undoped epitaxial InN, while growth conditions and thermodynamics have a less important role, contrary to what is observed in, e.g., GaN. Furthermore, the results imply that in high quality InN, the electron mobility is likely limited not by ionized point defect scattering, but rather by threading dislocations.
Proceedings of SPIE, the International Society for Optical Engineering | 2007
Floris Reurings; Filip Tuomisto
We have applied positron annihilation spectroscopy to study the role of gallium vacancies in the yellow luminescence of gallium nitride. We measured the Ga vacancy concentrations of a set of wurtzite GaN layers grown by metal-organic chemical-vapor deposition (MOCVD) on sapphire and containing different amounts of C and exhibiting different intensities in the yellow range of the photoluminescence spectrum. Interestingly, the relationship between the Ga vacancies, C impurities and yellow luminescence depends on the electrical conductivity of the material. In semi-insulating samples, we observe a correlation between the yellow luminescence and the carbon concentration, while there is anti-correlation between these two and the gallium vacancy concentration. In contrast, in the n-type samples both the yellow luminescence and the Ga vacancy concentration are independent of the carbon content. These results support the view that the gallium vacancy is not the only defect related to yellow luminescence observed in GaN, but that another, carbon-related mechanism is involved as well.
Journal of Applied Physics | 2013
A. Zubiaga; Floris Reurings; Filip Tuomisto; F. Plazaola; J. A. Garcia; A. Yu. Kuznetsov; W. Egger; J. Zuniga-Perez; V. Munoz-Sanjose
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 1017 cm−3 and 1018 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 r...
Physical Review B | 2010
Floris Reurings; Christian Rauch; Filip Tuomisto; Rebecca E. Jones; Kin Man Yu; W. Walukiewicz; W. J. Schaff
Physica Status Solidi (a) | 2010
Christian Rauch; Floris Reurings; Filip Tuomisto; T. D. Veal; C. F. McConville; Hai Lu; W. J. Schaff; Chad S. Gallinat; Gregor Koblmüller; James S. Speck; W. Egger; Benjamin Löwe; Luca Ravelli; Stanislav Sojak
Physica Status Solidi (c) | 2009
Floris Reurings; Filip Tuomisto; Chad S. Gallinat; Gregor Koblmüller; James S. Speck
Physica Status Solidi (a) | 2010
Floris Reurings; Filip Tuomisto; Werner Egger; Benjamin Löwe; Luca Ravelli; Sstanislav Sojak; Z. Liliental-Weber; Rebecca E. Jones; Kin Man Yu; W. Walukiewicz; W. J. Schaff
Applied Surface Science | 2006
Floris Reurings; A. Laakso; K. Rytsölä; A. Pelli; K. Saarinen
Archive | 2010
Floris Reurings