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    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.
  • [ X ]
    Öğe
    The effect of strain and spatial Bi distribution on the band alignment of GaAsBi single quantum well structure
    (Elsevier, 2021) Gunes, M.; Donmez, O.; Gumus, C.; Erol, A.; Alghamdi, H.; Alhassan, S.; Alhassni, A.
    The band line-up and band offset calculations of GaAs0.978Bi0.022/GaAs single quantum well with spatial changes of Bi composition were reported. The spatial Bi profile and a certain amount of the Bi composition in the barrier layer were determined by HR-XRD measurements. Virtual Crystal Approximation and Valence Band Anti-Crossing models were used including strain effects to obtain conduction and valence band edge shifts with Bi incorporation. Photoluminescence (PL) measurements were performed at a low temperature of 8 K as a function of excitation intensity. The PL spectra have shown asymmetric line shapes, which were fitted with different Gaussian functions. Comparing experimental PL results with calculated band edge energies, it was found that optical transition is a type I under low intensity excitation while the optical transition is switched from type I to type II due to the spatial changes in Bi concentrations. The band offsets Delta E-c/Delta E-v were also determined.