Department of Physics
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Browsing Department of Physics by Author "Aalizadeh, Majid"
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Item Open Access Current transport properties of (Au/Ni)/HfAlO3/n-Si metal–insulator–semiconductor junction(Elsevier Ltd, 2020-09-11) Arslan, Engin; Badali, Yosef; Aalizadeh, Majid; Altındal, Semsettin; Ozbay, EkmelIn this study, HfAlO3 ternary alloy thin film was grown on n-type silicon using the atomic layer deposition method. The current transport mechanisms in the (Au/Ni)/HfAlO3/n-Si junction were examined over a wide temperature range (80–360 K). The values obtained for the ideality factor (n) varied from 22.93 to 3.94 and the barrier height at zero bias (ФB0) ranged from 0.221 eV to 0.821 eV as the temperature changed from 80 to 360 K. The ΦB0–n and ΦB0–q/2 kT characteristics were investigated to explain the higher n values and non-ideal behavior of the Richardson curves. Two linear regions were found at low temperatures (LTs; 80–180 K) and high temperatures (HTs; 200–360 K), which indicated the presence of a Gaussian distribution barrier height and the average barrier heights (Φ‾B0) were identified. The values obtained for Φ‾Bo were 0.734 eV for LTs and 1.125 eV for HTs, and the values of σs were 0.085 V for LTs and 0.140 V for HTs. The values obtained for Nss decreased as the temperature increased and they varied between ~1012 and 1013 eV−1 cm−2. Finally, the dielectric behavior and conductivity of the (Au/Ni)/HfAlO3/n-Si junction were investigated at frequencies between 5 kHz and 2 MHz at room temperature. The values determined for ε′ and ε′′ at −1 V and 5 kHz were 2.1 and 3.53, respectively. © 2020Item Open Access Lithography-free, manganese-based ultrabroadband absorption through annealing-based deformation of thin layers into metal–air composites(OSA - The Optical Society, 2019-07-15) Aalizadeh, Majid; Khavasi, A.; Bütün, Bayram; Özbay, EkmelFabrication, characterization, and analysis of an ultrabroadband lithography-free absorber is presented. An over 94% average absorption is experimentally achieved in the wavelength range of 450–1400 nm. This ultrabroadband absorption is obtained by a simple annealed trilayer metal–insulator–metal (MIM) configuration. The metal used in the structure is manganese (Mn), which also makes the structure cost-effective. It is shown that the structure retains its high absorption for TM polarization, up to 70 deg, and, for TE polarization, up to 50 deg. Moreover, the physical mechanism behind this broadband absorption is explained. Being both lithography-free and cost-effective, the structure is a perfect candidate for large-area and mass production purposes.Item Open Access A route to unusually broadband plasmonic absorption spanning from visible to mid-infrared(Springer, 2019) Aalizadeh, Majid; Khavasi, A.; Serebryannikov, A. E.; Vandenbosch, G. A. E.; Özbay, EkmelIn this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e., for the wavelength varying from 478 to 3278 nm that yields an ultra-wide band with the width of 2800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin layer of Mn, the absorption bandwidth is reduced to 274 nm. Therefore, adding only a 5 nm layer of Mn leads to a more than tenfold increase in the width of the absorption band. It is explained in detail that the physical mechanism yielding this ultra-broadband result is a combination of plasmonic and non-plasmonic resonance modes, along with the appropriate optical properties of Mn. This structure has the relative bandwidth (RBW) of 149%, while only one step of lithography is required for its fabrication, so it is relatively simple. This makes it rather promising for practical applications.Item Open Access A simple mie-resonator based meta-array with diverse deflection scenarios enabling multifunctional operation at near-infrared(De Gruyter Open, 2020) Aalizadeh, Majid; Serebryannikov, A. E.; Özbay, Ekmel; Vandenbosch, G. A. E.Deflection, a basic functionality of wavefront manipulation is usually associated with the phase-gradient metasurfaces and the classical blazed gratings. We numerically and experimentally demonstrate an unusually wideband and simultaneously wide-angle deflection achieved at near-infrared in reflection mode for a periodic (nongradient), ultrathin meta-array comprising only one silicon nanorod (Mie resonator) per period. It occurs in the range where only the first negative diffraction order and zero order may propagate. Deflection serves as the enabler for multifunctional operation. Being designed with the main goal to obtain ultra-wideband and wide-angle deflection, the proposed meta-array is also capable in spatial filtering and wide-angle splitting. Spatial filtering of various types can be obtained in one structure by exploiting either deflection in nonzero diffraction orders, or the specular-reflection (zero-order) regime. Thus, the role of different diffraction orders is clarified. Moreover, on–off switching of deflection and related functionalities is possible by changing polarization state of the incident wave. The suggested device is simple to fabricate and only requires cost-effective materials, so it is particularly appropriate for the large-area fabrication using nanoprint lithography. Ultra-wideband wide-angle and other deflection scenarios, along with the other functionalities, are promising for applications in optical communications, laser optics, sensing, detection, and imaging.Item Open Access Temperature-mediated invocation of the vacuum state for switchable ultrawide-angle and broadband deflection(Nature Publishing Group, 2018) Serebryannikov, A. E.; Lakhtakia, A.; Aalizadeh, Majid; Özbay, Ekmel; Vandenbosch, G. A. E.Temperature-mediated appearance and disappearance of a deflection grating in a diffracting structure is possible by employing InSb as the grating material. InSb transits from the dielectric state to the plasmonic state in the terahertz regime as the temperature increases, this transition being reversible. An intermediate state is the vacuum state in which the real part of the relative permittivity of InSb equals unity while the imaginary part is much smaller. Then the grating virtually disappears, deflection being impossible as only specular reflection can occur. This ON/OFF switching of deflection and relevant angular filtering are realizable over wide ranges of frequency and incidence angle by a temperature change of as low as 20 K. The vacuum state of InSb invoked for ON/OFF switching of deflection and relevant angular filtering can also be obtained for thermally tunable materials other than InSb as well as by using non-thermal mechanisms.Item Open Access Toward electrically tunable, lithography-free, ultra-thin color filters covering the whole visible spectrum(Nature Publishing Group, 2018) Aalizadeh, Majid; Serebryannikov, A. E.; Khavasi, A.; Vandenbosch, G. A. E.; Özbay, EkmelThe possibility of real-time tuning of optical devices has attracted a lot of interest over the last decade. At the same time, coming up with simple lithography-free structures has always been a challenge in the design of large-area compatible devices. In this work, we present the concept and the sample design of an electrically tunable, lithography-free, ultra-thin transmission-mode color filter, the spectrum of which continuously covers the whole visible region. A simple Metal-Insulator-Metal (MIM) cavity configuration is used. It is shown that using the electro-optic dielectric material of 4-dimethyl-amino-N-methyl-4-stilbazoliumtosylate (DAST) as the dielectric layer in this configuration enables efficient electrical tuning of the color filter. The total thickness of the structure is 120 nm, so it is ultra-thin. The output color gets tuned from violet to red by sweeping the applied voltage from −12 to +12 Volts (V). We present an in-detail optimization procedure along with a simple calculation method for the resonance wavelength of the MIM cavity that is based on circuit theory. Such power-efficient structures have a large variety of potential applications ranging from optical communication and switching to displays and color-tunable windows.