Browsing by Author "Prozheeva, V."

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  • Effects of alloy composition and Si-doping on vacancy defect formation in (InxGa1- x)2O3 thin films
    (2018-03-28) Prozheeva, V.; Hölldobler, R.; Von Wenckstern, H.; Grundmann, M.; Tuomisto, F.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Various nominally undoped and Si-doped (InxGa1- x)2O3 thin films were grown by pulsed laser deposition in a continuous composition spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterisation technique in order to investigate the effect of alloy composition and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concentrations changing to In2O3-like behaviour along with the increase in the indium fraction. Increasing indium concentration is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron saturation trapping in VIn-like defects, suggesting a vacancy concentration of at least mid-1018 cm-3 independent of the indium content.
  • Evaluation of the concentration of point defects in GaN
    (2017-12-01) Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu N.; Prozheeva, V.; Makkonen, I.; Tuomisto, F.; Leach, J. H.; Udwary, K.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Photoluminescence (PL) was used to estimate the concentration of point defects in GaN. The results are compared with data from positron annihilation spectroscopy (PAS), secondary ion mass spectrometry (SIMS), and deep level transient spectroscopy (DLTS). Defect-related PL intensity in undoped GaN grown by hydride vapor phase epitaxy increases linearly with the concentration of related defects only up to 1016 cm-3. At higher concentrations, the PL intensity associated with individual defects tends to saturate, and accordingly, does not directly correlate with the concentration of defects. For this reason, SIMS analysis, with relatively high detection limits, may not be helpful for classifying unidentified point defects in GaN. Additionally, we highlight challenges in correlating defects identified by PL with those by PAS and DLTS methods.
  • 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.
  • Structural, optical, and electrical properties of orthorhombic κ -(In x Ga 1-x ) 2 O 3 thin films
    (2019-02-01) Hassa, A.; Von Wenckstern, H.; Splith, D.; Sturm, C.; Kneiß, M.; Prozheeva, V.; Grundmann, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Material properties of orthorhombic κ-phase (In x Ga 1-x ) 2 O 3 thin films grown on a c-plane sapphire substrate by pulsed-laser deposition are reported for an indium content up to x ∼ 0.35. This extended range of miscibility enables band gap engineering between 4.3 and 4.9 eV. The c-lattice constant as well as the bandgap depends linearly on the In content. For x > 0.35, a phase change to the hexagonal InGaO 3 (ii) and the cubic bixbyite structure occurred. The dielectric function and the refractive index were determined by spectroscopic ellipsometry as a function of the alloy composition. We propose zirconium to induce n-type conductivity and have achieved electrically conducting thin films with a room temperature conductivity of up to 0.1 S/cm for samples with a low In content of about x = 0.01. Temperature-dependent Hall-effect measurements yielded a thermal activation energy of the free electron density of 190 meV. Schottky barrier diodes with rectification ratios up to 10 6 were investigated by quasi-static capacitance voltage and temperature-dependent current voltage measurements.