Browsing by Author "Speck, J. S."

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Compensating vacancy defects in Sn- and Mg-doped In 2O3
(2014) Korhonen, E.; Tuomisto, Filip; Bierwagen, O.; Speck, J. S.; Galazka, Z.
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
MBE-grown Sn- and Mg-doped epitaxial In2O3 thin-film samples with varying doping concentrations have been measured using positron Doppler spectroscopy and compared to a bulk crystal reference. Samples were subjected to oxygen or vacuum annealing and the effect on vacancy type defects was studied. Results indicate that after oxygen annealing the samples are dominated by cation vacancies, the concentration of which changes with the amount of doping. In highly Sn-doped In2O3, however, these vacancies are not the main compensating acceptor. Vacuum annealing increases the size of vacancies in all samples, possibly by clustering them with oxygen vacancies.
Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature
(2010) Koblmuller, G.; Reurings, F.; Tuomisto, Filip; Speck, J. S.
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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