Browsing by Author "Şahin, Mehmet"

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Advanced tunability of optical properties of CdS/ZnSe/ZnTe/CdSe multi-shell quantum dot by the band edge engineering
(ELSEVIER, 2022) Koc, Fatih; Kavruk, Ahmet Emre; Sahin, Mehmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, the advanced manipulability of wave functions in a type-II multi-shell hetero-nanostructure (MS-HNS) and the tunability of radiative exciton lifetime over a wide range with and/or without changing in transition energies has been demonstrated by the band edge engineering. For this purpose, the electronic and optical properties of exciton (X) and biexciton (XX) in a spherical CdS/ZnSe/ZnTe/CdSe HNS have been explored in detail. In the calculations, effects of all Coulombic interactions between the charges have been taken into account on the wave functions. Moreover, in the case of XX, the exchange–correlation potential between the same charged particles has also been considered. The results have been presented as a function of CdS core radius and ZnSe shell thickness and the probable physical reasons have been discussed in detail.
The electronic properties of a core/shell/well/shell spherical quantum dot with and without a hydrogenic impurity
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Sahin, Mehmet; Tas, Hatice; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have performed a detailed investigation of the electronic properties of a core/shell/well/shell multi-layered spherical quantum dot, such as energy eigenvalues, wave functions, electron probability distribution and binding energies. The energy eigenvalues and their wave functions of the considered structure have been calculated for cases with and without an on-center impurity. For this purpose, the Schr¨odinger equation has been numerically solved by using the shooting method in the effective mass approximation for a finite confining potential. The electronic properties have been examined for different core radii, barrier thickness and well widths in a certain potential. The results have been analyzed in detail as a function of the layer thickness and their physical reasons have been interpreted. It has found that the electronic properties are strongly depending on the layer thickness.
The inter-sublevel optical properties of a spherical quantum dot-quantum well with and without a donor impurity
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Tas, Hatice; Sahin, Mehmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have investigated the inter-sublevel optical properties of a core/shell/well/shell spherical quantum dot with the form of quantum dot-quantum well heterostructure. In order to determine the energy eigenvalues and corresponding wave functions, the Schr¨odinger equation has been solved full numerically by using shooting method in the effective mass approximation for a finite confining potential. The inter-sublevel optical absorption and the oscillator strength between ground (1s) and excited (1p) states have been examined based on the computed energies and wave functions. Also, the effect of a hydrogenic donor impurity, located at the center of the multi-shell spherical quantum dot (MSQD), has been researched for different core radii (R1), shell thicknesses (Ts) and well widths (Tw) in certain potential. It is observed that the oscillator strengths and the absorption coefficients are strongly depend on the core radii and layer thicknesses of the MSQD.
A model for the recombination and radiative lifetime of trions and biexcitons in spherically shaped semiconductor nanocrystals
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2013) Şahin, Mehmet; Koç, Fatih; 0000-0002-4751-2340; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this letter, we propose a different model to determine the recombination oscillator strength of trions and biexcitons for bound and unbound cases in the effective mass approximation. The validity of our model has been confirmed by the radiative lifetime of the trion and biexciton in a spherical quantum dot. The results show that the model works with sufficient accuracy in comparison with results of more complex methods such as quantum Monte Carlo techniques and atomistic calculations.
The photoionization cross section of a hydrogenic impurity in a multi-layered spherical quantum dot
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Sahin, Mehmet; Tek, Firdes; Erdinc, Ahmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have investigated the photoionization cross section of an on-center hydrogenic impurity in a multi-layered spherical quantum dot. The electronic energy levels and their wave functions have been determined fully numerically by shooting method. Also, we have calculated the binding energy of the impurity by using these energy values. The photoionization cross section has also been computed as a function of the layer thickness and normalized photon energies. We have discussed in detail the possible physical reasons behind the changes in the binding energies and photoionization cross section. It is observed that both the binding energies and the photoionization cross sections depend strongly on the layer thickness and photon energies. (C) 2012 American Institute of Physics.