Yazar "Ukelge, M. O." seçeneğine göre listele

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    Öğe
    A comparative photoluminescence study on Mn-Free GaAs/AlAs and Mn-containing Ga1-xMnxAs/AlAs quantum wells (QWs) grown on various orientations by MBE
    (Taylor & Francis Ltd, 2016) Gunes, M.; Erken, O.; Gumus, C.; Yalaz, E.; Pesen, E.; Ukelge, M. O.; Arpapay, B.
    Optical properties of diluted magnetic semiconductor Ga0.999Mn0.001As/AlAs quantum well structures grown on (1 0 0 ), (1 1 0), (3 1 1)B and (4 1 1)B by molecular beam epitaxy are reported. Temperature-dependent spectral photoluminescence (PL) measurement was performed at temperatures between 15 and 300K. The PL measurements showed that band gap of the alloy decreases with increasing lattice temperature regardless the growth orientations. S-shaped temperature dependence has been observed in the samples grown on (1 0 0), (3 1 1)B, (4 1 1)B orientations. PL emission energy is fitted with Varshni and Bose-Einstein Approximation to determine Debye temperature (beta), (Theta(E)) and thermal expansion coefficient (alpha), the exciton-phonon coupling strength (a(B)).
  • [ X ]
    Öğe
    Optical properties of GaAs1-xBix/GaAs quantum well structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates
    (Iop Publishing Ltd, 2018) Gunes, M.; Ukelge, M. O.; Donmez, O.; Erol, A.; Gumus, C.; Alghamdi, H.; Galeti, H. V. A.
    In this work, the electronic bandstructure of GaAs1-xBix/GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 <= x <= 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C-BiM) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively.