Browsing by Subject "Quantum structure"
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Item Open Access Blue InGaN/GaN-based quantum electroabsorption modulators(IEEE, 2006) Sarı, Emre; Nizamoğlu, Sedat.; Özel, Tuncay; Demir, Hilmi VolkanWe introduce InGaN/GaN-based quantum electroabsorption modulator that incorporates ∼5 nm thick In0.35Ga0.65N/GaN quantum structures for operation in the blue spectral range of 420-430 nm. This device exhibits an optical absorption coefficient change of ∼6000 cm-1 below the band edge at highly transmissive, blue region (at λ peak=424 nm) with a 6 V swing and emits blue light (at λpeak=440 nm) with an optical output power of 0.35 mW at a 20 mA current injection level. Unlike infrared III-V quantum modulators, this blue modulator shows a blue shift in its electroabsorption (for λ < 418 nm) with increasing applied field accross it, due to high alternating polarization fields in its quantum structures; this electroabsorption behavior is opposite to the conventional quantum confined Stark effect that features common red shift. This device holds great promise for > 10 GHz optical clock injection directly into silicon CMOS chips in the blue because of its low parasitic in-series resistance (< 100 Ω) and the possibility to make smaller device mesas for low capacitance (1.2 fF for a 10μm×10μm mesa size). Considering high-speed operation and high responsivity of silicon-on-insulator (SOI) photodetectors in the blue range, unlike in the infrared, this approach eliminates the need for on-chip hybrid integration of Si CMOS with III-V photodetectors. Furthermore, the efficient electroluminescence of this device makes it feasible to consider on-chip blue laser-modulator integration for a compact optical clocking scheme. © 2006 IEEE.Item Open Access Controlled growth and characterization of epitaxially-laterally-overgrown InGaN/GaN quantum heterostructures(IEEE, 2010) Sarı, Emre; Akyuz, Özgün; Choi, E. -G.; Lee I.-H.; Baek J.H.; Demir, Hilmi VolkanCrystal material quality is fundamentally important for optoelectronic devices including laser diodes and light emitting diodes. To this end epitaxial lateral overgrowth (ELO) has proven to be a powerful technique for reducing dislocation density in GaN and its alloys [1,2]. Implementation and design of ELO process is, however, critical for obtaining high-quality material with high-efficiency quantum structures for light emitters [3]. ©2010 IEEE.Item Open Access Formation of quantum structures on a single nanotube by modulating hydrogen adsorption(American Physical Society, 2003) Gülseren, O.; Yildirim, T.; Çıracı, SalimUsing first-principles density functional calculations we showed that quantum structures can be generated on a single carbon nanotube by modulating the adsorption of hydrogen atoms. The band gap of the hydrogen-free zone of the tube widens in the adjacent hydrogen covered zone. The sudden variation of the band gap leads to band offsets at the conduction- and valence-band edges. At the end, the band gap of the whole system is modulated along the axis of the tube, which generates quantum wells or quantum dots. Specific electronic states are confined in these quantum wells. The type and radius of the nanotube and the extent and sequence of hydrogen-free and hydrogen-covered zones can provide several options to design a desired optoelectronic nanodevice.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.