Browsing by Subject "Absorption edges"
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Item Open Access Generation of InN nanocrystals in organic solution through laser ablation of high pressure chemical vapor deposition-grown InN thin film(Springer, 2012-07-27) Alkis, S.; Alevli, M.; Burzhuev, S.; Vural, H. A.; Okyay, Ali Kemal; Ortaç, B.We report the synthesis of colloidal InN nanocrystals (InN-NCs) in organic solution through nanosecond pulsed laser ablation of high pressure chemical vapor deposition-grown InN thin film on GaN/sapphire template substrate. The size, the structural, the optical, and the chemical characteristics of InN-NCs demonstrate that the colloidal InN crystalline nanostructures in ethanol are synthesized with spherical shape within 5.9-25.3, 5.45-34.8, 3.24-36 nm particle-size distributions, increasing the pulse energy value. The colloidal InN-NCs solutions present strong absorption edge tailoring from NIR region to UV region.Item Open Access High efficiency monolithic photodetectors for integrated optoelectronics in the near infrared(IEEE, 2009) Okyay, Ali Kemal; Onbaşlı, M. Cengiz; Ercan, Burcu; Yu H.-Y.; Ren, S.; Miller, D.A.B.; Saraswat, K.C.; Nayfeh, A.M.Monolithic Germanium photodetectors integrated on Si with external efficiency up to 68% at 1550nm and low dark current density 3.2mA/cm2 are demonstrated. The absorption edge red shifted by 47nm corresponding to bandgap energy reduced by 24meV. © 2009 IEEE.Item Open Access Polar vs. nonpolar InGaN/GaN quantum heterostructures: Opposite quantum confined electroabsorption and carrier dynamics behavior(IEEE, 2010) Sarı, Emre; Nizamoğlu, Sedat; Choi J.H.; Lee, S.J.; Baik, K.H.; Lee I.H.; Baek J.H.; Hwang, S.-M.; Demir, Hilmi VolkanWe present a study of quantum confined electroabsorption and carrier dynamics in polar c-plane and nonpolar a-plane InGaN/GaN quantum heterostructures. We demonstrate red-shifting absorption edge, due to quantum confined Stark effect, in nonpolar InGaN/GaN quantum structures in response to increased electric field, while we show the opposite effect with blue-shifting absorption spectra in polar quantum structures. Moreover, confirmed by time-resolved photoluminescence measurements, we prove that carrier lifetimes increase with increasing electric field for nonpolar structures, whereas the opposite occurs for polar ones.Item Open Access Post-Treatment od Silicon Nanocrystals Produced by Ultra-Short Pulsed Laser Ablation in Liquid: Toward Blue Luminescent Nanocrystal Generation(American Chemical Society, 2012-01-11) Alkis, S.; Okyay, Ali Kemal; Ortac, B.Blue luminescent colloidal silicon nanocrystals (Si-NCs) were produced in a two-stage process. In the first step, synthesis of Si-NCs was achieved by femtosecond pulsed laser ablation of a silicon wafer, which was immersed in deionized water. The size and the structural and the chemical characteristics of colloidal Si-NCs were investigated by TEM and EDAX analyses, and it is found out that the Si-NCs are in spherical shape and the particle diameters are in the range of 5-100 nm. In the second step, ultrasonic waves and filtering chemical-free post-treatment of colloidal Si-NCs solution was performed to reduce the particle size. High-resolution TEM (HRTEM) studies on post-treated colloidal solution clearly show that small (1-5.5 nm in diameter) Si-NCs were successfully produced. Raman spectroscopy results clearly confirms the generation of Si nanoparticles in the crystalline nature, and the Raman scattering study of post-treated Si-NCs confirms the reduction of the particle size. The UV-vis absorption and photoluminescence (PL) spectroscopy studies elucidate the quantum confinement effect of Si-NCs on the optical properties. The colloidal Si-NCs and post-treated Si-NCs solutions present strong absorption edge shifts toward UV region. Broadband PL emission behavior is observed for the initial colloidal Si-NCs, and the PL spectrum of post-treated Si-NCs presents a blue-shifted broadband PL emission behavior due to the particle size reduction effect.