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    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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    Experimental and Theoretical Study of Defect Evolution in InSb Epilayers under Gamma Irradiation: A Comparative Analysis of MOCVD vs MBE Growth Methods
    (American Chemical Society, 2025) Marroquin, John Fredy Ricardo; Derc, Alex Cortes; Nascimento Lima, Erika; de Oliveira, Igor Saulo Santos; Gunes, Mustafa; Akyol, Mustafa; Archanjo, Braulio S.; de Azevedo, Walter M.; Henini, Mohamed; Felix, Jorlandio Francisco
    The operational requirements of high-radiation and extraterrestrial environments highlight the need to evaluate narrow-bandgap semiconductors that remain unexplored under such conditions, among them Indium Antimonide (InSb). As a material system, InSb offers unparalleled electron mobility and a massive g-factor, making it indispensable for next-generation infrared detection, Hall sensing, and topological quantum computing architectures. However, the practical realization of these devices is frequently hindered by the necessity of heteroepitaxial growth on lattice-mismatched substrates, typically Gallium Arsenide (GaAs), which introduces a complex landscape of threading dislocations and interfacial defects. This report presents an exhaustive, multimodal investigation into the radiation hardness of InSb epilayers, specifically contrasting the microstructural evolution of films grown via Metal-Organic Chemical Vapor Deposition (MOCVD) against those synthesized by Molecular Beam Epitaxy (MBE). Utilizing an experimental framework that integrates Electron Paramagnetic Resonance (EPR), Raman spectroscopy, High-Resolution Scanning Transmission Electron Microscopy (HR-STEM), and ab initio Density Functional Theory (DFT), this study elucidates the mechanistic divergence in radiation response between the two growth methodologies. The data reveal a critical, counterintuitive trade-off: the MOCVD-grown material, despite exhibiting superior initial crystalline quality driven by a zinc-doped seed layer that passivates interfacial traps, demonstrates a heightened susceptibility to electronic degradation and stoichiometry violation under high-fluence Gamma (gamma) irradiation. In contrast, the MBE-grown material, initially marred by a higher density of dislocations, exhibits a complex survivability mode at elevated doses, characterized by defect saturation. This report details the atomic-level physics driving these behaviors, including the radiation-induced formation of homopolar Sb-Sb bonds, the symmetry-breaking anisotropy of the g-factor, and the thermodynamic instability of dopant-passivated interfaces under nonequilibrium conditions. Furthermore, these findings can be used as actionable engineering guidelines for Radiation Hardness Assurance (RHA), proposing novel nondestructive spectroscopic metrics for the qualification of semiconductors destined for space and nuclear applications.
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    Öğe
    Structural and optical properties of diluted magnetic Ga1-xMnxAs-AlAs quantum wells grown on high-index GaAs planes
    (Indian Acad Sciences, 2017) Gunes, Mustafa; Gumus, Cebrail; Gobato, Yara Galvao; Henini, Mohamed
    We report on the structural and optical properties of Ga1-xMnxAs-AlAs quantum wells (QWs) with x = 0.1% grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates with orientations (100), (110), (311)B and (411)B. Atomic force microscopy (AFM), X-ray diffraction (XRD) and photoluminescence (PL) techniques were used to investigate these QWs. AFM results have evidenced the formation of Mn-induced islands, which are randomly distributed on the surface. These islands tend to segregate for samples grown on (110) and (411)B planes, while no clear segregation was observed for samples grown on (100) and (311)B orientations. Results show that the PL line width increases with Mn segregation. XRD measurements were used to determine 2 theta, d and cell parameters.