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    Öğe
    Analysis of mixed optical transitions in dilute magnetic AlAs/GaAs/ GaMnAs quantum wells grown on high substrate index by molecular beam epitaxy
    (Elsevier, 2023) Kerimova, Shemshat; Donmez, Omer; Gunes, Mustafa; Kuruoglu, Furkan; Aydin, Mustafa; Gumus, Cebrail; Erol, Ayse
    In this study, we report the influence of high-index substrate orientation on the optical properties of dilute Mn containing a single quantum well (QW) structure grown by molecular beam epitaxy (MBE). The electronic band structure of the samples is calculated with finite element methods (FEM). Photomodulated reflectance (PR) spectroscopy is employed to determine the optical transition energies at room temperature. PR experimental results are analyzed with the Third Derivative Functional Form (TDFF) signal function. TDFF fitting shows that the optical transition starts below the fundamental GaAs bandgap energy for the samples grown on (311) B and (411) B-oriented substrates. Comparing TDFF fitting and calculated optical transition energies with FEM show that the optical transition occurs in type-I and type-II as direct and indirect transitions, respectively. Type-I and -II optical transitions are addressed concerning the electronic band structure of the sample grown on oriented substrates.
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    Öğe
    Determination of electronic band structure of quaternary ferromagnetic Ga0.97-yMn0.03CryAs epitaxial layers
    (Elsevier, 2023) Donmez, Omer; Gunes, Mustafa; Henini, Mohamed; Erol, Ayse
    Introducing transition metals to conventional III-V semiconductors anomalously changes their fundamental characteristics, such as electronic, magnetic, and structural properties. In this study, we show that the valence band anti-crossing (VBAC) model can be exploited to calculate the electronic band structure of the quaternary Ga0.97-xMn0.03CrxAs epitaxial layers. In this model, the localized Mn and Cr defect states interact with the valence band states (VB), reconstructing VBs and splitting each VB state. The splitting top of the VB state forms an impurity band (IB) and fundamental VB edge. Photomodulated reflectance (PR) spectroscopy is exploited to determine optical transition energies at room temperature. PR spectra were analyzed with the third derivative functional form (TDFF) signal's line shape. The experimental optical transition energies, including band-to-band and spin split-off band transitions, match the calculated optical transition energies by the VBAC model. In the calculation, the interaction energy between localized Mn/Cr-energy level and valence band edges is experi-mentally determined as 0.7 eV.
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    Öğe
    Magnetotransport study on as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs strained quantum well structures
    (Springeropen, 2014) Donmez, Omer; Sarcan, Fahrettin; Erol, Ayse; Gunes, Mustafa; Arikan, Mehmet Cetin; Puustinen, Janne; Guina, Mircea
    We report the observation of thermal annealing- and nitrogen-induced effects on electronic transport properties of as-grown and annealed n- and p-type modulation-doped Ga1-xInxNyAs1-y (x = 0.32, y = 0, 0.009, and 0.012) strained quantum well (QW) structures using magnetotransport measurements. Strong and well-resolved Shubnikov de Haas (SdH) oscillations are observed at magnetic fields as low as 3 T and persist to temperatures as high as 20 K, which are used to determine effective mass, 2D carrier density, and Fermi energy. The analysis of temperature dependence of SdH oscillations revealed that the electron mass enhances with increasing nitrogen content. Furthermore, even the current theory of dilute nitrides does not predict a change in hole effective mass; nitrogen dependency of hole effective mass is found and attributed to both strain- and confinement-induced effects on the valence band. Both electron and hole effective masses are changed after thermal annealing process. Although all samples were doped with the same density, the presence of nitrogen in n-type material gives rise to an enhancement in the 2D electron density compared to the 2D hole density as a result of enhanced effective mass due to the effect of nitrogen on conduction band. Our results reveal that effective mass and 2D carrier density can be tailored by nitrogen composition and thermal annealing-induced effects.