Browsing by Subject "Epitaxial growth"
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Item Open Access Ab initio temperature dependent studies of the homoepitaxial growth on Si(0 0 1) surface(2001) Dağ, S.; Çıracı, Salim; Kılıç, Ç.; Fong, C. Y.We performed ab initio zero temperature and finite temperature molecular dynamics calculations to investigate the homoepitaxial growth on the Si(0 0 1) surface. How do the deposited atoms (adatoms) form addimers and how do the addimers reach their favorable positions at the nucleation site of the growth process are presented. Once two epitaxial addimers, one over the dimer row and oriented perpendicular to the surface dimer bonds and the other over the adjacent trough, are aligned at high temperature, the nucleation site of the growth process is formed. The concerted bond exchange between these addimers and the reconstructed surface dimers is found to be the atomistic mechanism that leads to the homoepitaxial growth. © 2001 Elsevier Science B.V.Item Open Access Atomic scale investigation of clean and epi-grown Si(001) surfaces using scanning tunneling microscopy(Bilkent University, 1996) Özer, H. ÖzgürIn this thesis, clean and epi-grown Si(001)(2x1)surfaces are analyzed by Scanning Tunneling Microscopy (STM). The STM and Ultra High Vacuum System (UHV) in which the microscope is installed, are described. A brief history of the studies on the reconstruction and fundamental features of the Si(001) surface is also given. First, the sample and tip preparation techniques were optimized. Sample preparation method, which includes both ex situ chemical and in situ heating cleaning procedures, was found not to give routinely the clean and atomically flat surfaces, because of the criticality of the temperature values used during heat treatments. The monoatomic steps, dimer rows, defects such as missing dimer and dimer groups, were observed on clean Si(001) surfaces. Double height step formation due to contamination was also detected on a few samples. Buckling of dimers, which is believed to be due mainly to either the high defect density or tip-surface interaction, was observed on one sample. Si and Ge were grown epitaxially on the silicon substrate, with 0.11 ML and 3.2 ML coverages, respectively. The Si growth on Si(001) was found to occur as island formation because of the low substrate temperature (ca. 300 degrees C). Strong shape anisotropy and diffusional anistropy in the growth have been observed. On the other hand, the large coverage of Ge on Si(001) at a relatively high substrate temperature (ca. 500 degrees C) resulted in step flow growth rather than individual island formation on the terraces.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 Defect reduction of Ge on Si by selective epitaxy and hydrogen annealing(2008-10) Yu, H.-Y.; Park, J.-H.; Okyay, Ali Kemal; Saraswat, K. C.We demonstrate a promising approach for the monolithic integration of Ge-based nanoelectronics and nanophotonics with S-ilicon: the selective deposition of Ge on Si by Multiple Hydrogen Annealing for Heteroepitaxy (MHAH). Very high quality Ge layers can be selectively integrated on Si CMOS platform with this technique. We confirm the reduction of dislocation density in Ge layers using AFM surface morphology study. In addition, in situ doping of Ge layers is achieved and MOS capacitor structures are studied. ©The Electrochemical Society.Item Open Access Effect of growth pressure on coalescence thickness and crystal quality of GaN deposited on 4H-SiC(Elsevier, 2010-09-25) Caban, P.; Strupinski, W.; Szmidt, J.; Wojcik, M.; Gaca, J.; Kelekci, O.; Caliskan, D.; Özbay, EkmelThe influence of growth pressure on the coalescence thickness and the crystal quality of GaN deposited on 4HSiC by low pressure metalorganic vapor phase epitaxy was studied. It was shown that growth pressure has an impact on the surface roughness of epilayers and their crystal quality. GaN coalescence thicknesses were determined for the investigated growth pressures. The GaN layers were characterized by AFM and HRXRD measurements. HEMT structures were also fabricated and characterized. Among the growth pressures studied, 50, 125 and 200 mbar, 200 mbar was found to be most suitable for GaN/SiC epitaxy.Item Open Access Experimental and theoretical investigation of phosphorus in-situ doping of germanium epitaxial layers(Elsevier, 2013) Yu, H. -Y.; Battal, E.; Okyay, Ali Kemal; Shim, J.; Park J. -H.; Baek, J. W.; Saraswat, K. C.We investigate phosphorus in-situ doping characteristics in germanium (Ge) during epitaxial growth by spreading resistance profiling analysis. In addition, we present an accurate model for the kinetics of the diffusion in the in-situ process, modeling combined growth and diffusion events. The activation energy and pre-exponential factor for phosphorus (P) diffusion are determined to be 1.91 eV and 3.75 × 10-5 cm2/s. These results show that P in-situ doping diffusivity is low enough to form shallow junctions for high performance Ge devices.Item Open Access High performance n-MOSFETs with novel source/drain on selectively grown Ge on Si for monolithic integration(IEEE, 2009) Yu, H.-Y.; Kobayashi, M.; Jung, W. S.; Okyay, Ali Kemal; Nishi, Y.; Saraswat, K. C.We demonstrate high performance Ge n-MOSFETs with novel raised source/drain fabricated on high quality single crystal Ge selectively grown heteroepitaxially on Si using Multiple Hydrogen Anealing for Heteroepitaxy(MHAH) technique. Until now low source/drain series resistance in Ge n-MOSFETs has been a highly challenging problem. Source and drain are formed by implant-free, in-situ doping process for the purpose of very low series resistance and abrupt and shallow n+/p junctions. The novel n-MOSFETs show among the highest electron mobility reported on (100) Ge to-date. Furthermore, these devices provide an excellent Ion/Ioff ratio(4× 103) with very high Ion of 3.23μA/μm. These results show promise towards monolithic integration of Ge MOSFETs with Si CMOS VLSI platform.Item Open Access High-performance solar-blind AlGaN Schottky photodiodes(Materials Research Society, 2003) Bıyıklı, Necmi; Kartaloglu, T.; Aytur, O.; Kimukin, I.; Özbay, EkmelHigh-performance solar-blind AlGaN-based Schottky photodiodes have been demonstrated. The detectors were fabricated on MOCVD-grown AlGaN/GaN heterostructures using a microwave-compatible fabrication process. Current-voltage, spectral responsivity, noise, and high-speed characteristics of the detectors were measured and analyzed. Dark currents lower than 1 pA at bias voltages as high as 30 V were obtained. True solar-blind detection was achieved with a cut-off wavelength lower than 266 nm. A peak device responsivity of 78 mA/W at 250 nm was measured under 15 V reverse bias. A visible rejection of more than 4 orders of magnitude was observed. The solar-blind photodiodes exhibited noise densities below the measurement setup noise floor of 3×10 -29 A 2/Hz around 10 KHz. High-speed measurements at the solar-blind wavelength of 267 nm resulted in 3-dB bandwidths as high as 870 MHz.Item Open Access High-Speed InSb photodetectors on GaAs for mid-IR applications(IEEE, 2004) Kimukin, I.; Bıyıklı, Necmi; Kartaloǧlu, T.; Aytür, O.; Özbay, EkmelWe report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06 × 10 -6 cm 2 to 2.25 × 10 -4 cm 2 measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 Ω cm 2. At 77 K, spectral measurements yielded high responsivity between 3 and 5 μm with the cutoff wavelength of 5.33 μm. The maximum responsivity tor 80-μm diameter detectors was 1.00 × 10 5 V/W at 435 μm while the detectivity was 3.41×10 9 cm Hz 1/2/W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 μm with the pump at 780 mm. 30-μm diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.Item Open Access High-speed solar-blind AlGaN Schottky photodiodes(Cambridge University Press, 2003) Bıyıklı, Necmi; Kimukin, İbrahim; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, EkmelWe report high-speed solar-blind AlGaN-based Schottky photodiodes. AlGaN/GaN heterostructure device layers were grown on sapphire substrate. The devices were fabricated on AlGaN/GaN heterostructuresusing a microwave compatible fabrication process. Schottky photodiodes with Au and indium-tin-oxide (ITO) Schottky contacts were fabricated. Current-voltage, spectral responsivity, and high-speed measurements were performed. Both Schottky samples exhibited very low sub-pA dark currents at high reverse bias. A bias dependent spectral responsivity was observed with a peak responsivity of 89 mA/W at 267 nm, and 44 mA/W at 263 nm for Au and ITO-Schottky devices respectively. Time-based high-frequency measurements at 267 nm resulted in pulse responses with rise times and pulse-widths as short as 13 ps and 74 ps respectively. The fastest solar-blind detector had a record 3-dB bandwidth of 1.10 GHz.Item Open Access High-speed visible-blind resonant cavity enhanced AlGaN Schottky photodiodes(Materials Research Society, 2003) Bıyıklı, Necmi; Kartaloglu, T.; Aytur, O.; Kimukin, I.; Özbay, EkmelWe have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/Al 0.2Ga 0.8N Bragg mirror. The devices were fabricated using a microwave compatible fabrication process. Au and indium-tin-oxide (ITO) thin films were used for Schottky contact formation. ITO and Au-Schottky devices exhibited resonant peaks with 0.153 A/W and 0.046 A/W responsivity values at 337 nm and 350 nm respectively. Temporal high-speed measurements at 357 nm resulted in fast pulse responses with pulse widths as short as 77 ps. The fastest UV detector had a 3-dB bandwidth of 780 MHz.Item Open Access InGaN/GaN based LEDs with electroluminescence in violet, blue, and green tuned by epitaxial growth temperature(IEEE, 2007) Sarı, Emre; Nizamoğlu, Sedat; Özel, Tuncay; Demir, Hilmi Volkan; İnal, Ayşe; Ülker, Erkin; Özbay, Ekmel; Dikme, Y.; Heuken, M.In this work, we present a full set of InGaN LEDs based on a single optimal InGaN/GaN quantum design with emission wavelengths spanning from green to blue to violet by tuning the active layer growth temperature to precisely control InN incorporation into the quantum structures.Item Open Access Integrated AlGaN quadruple-band ultraviolet photodetectors(IOP Publishing, 2012-04-27) Gökkavas, M.; Butun, S.; Caban, P.; Strupinski, W.; Özbay, EkmelMonolithically integrated quadruple back-illuminated ultraviolet metalsemiconductormetal photodetectors with four different spectral responsivity bands were demonstrated on each of two different Al xGa 1-xN heterostructures. The average of the full-width at half-maximum (FWHM) of the quantum efficiency peaks was 18.15nm for sample A, which incorporated five 1000nm thick epitaxial layers. In comparison, the average FWHM for sample B was 9.98 nm, which incorporated nine 500nm thick epitaxial layers.Item Open Access Low-temperature and high-quality growth of Bi2O2Se layered semiconductors via cracking metal–organic chemical vapor deposition(American Chemical Society, 2021-05-25) Kang, M.; Chai, H. J.; Jeong, H. B.; Park, C.; Jung, In-Y.; Park, E.; Çiçek, Mert Miraç; Lee, I.; Bae, B. S.; Durgun, Engin; Kwak, J. Y.; Song, S.; Choi, S. Y.; Jeong, Hu Y.; Kang, K.Ternary metal-oxy-chalcogenides are emerging as next-generation layered semiconductors beyond binary metal-chalcogenides (i.e., MoS2). Among ternary metal-oxy-chalcogenides, especially Bi2O2Se has been demonstrated in field-effect transistors and photodetectors, exhibiting ultrahigh performance with robust air stability. The growth method for Bi2O2Se that has been reported so far is a powder sublimation based chemical vapor deposition. The first step for pursuing the practical application of Bi2O2Se as a semiconductor material is developing a gas-phase growth process. Here, we report a cracking metal–organic chemical vapor deposition (c-MOCVD) for the gas-phase growth of Bi2O2Se. The resulting Bi2O2Se films at very low growth temperature (∼300 °C) show single-crystalline quality. By taking advantage of the gas-phase growth, the precise phase control was demonstrated by modulating the partial pressure of each precursor. In addition, c-MOCVD-grown Bi2O2Se exhibits outstanding electrical and optoelectronic performance at room temperature without passivation, including maximum electron mobility of 127 cm2/(V·s) and photoresponsivity of 45134 A/W.Item Open Access Model study of a surfactant on the GaAs(100) surface(Elsevier, 2002-11-01) Consorte, C. D.; Fong, C. Y.; Watson, M. D.; Yang, L. H.; Çıracı, SalimBased on the facts that: (a) the transverse acoustic vibrational branch frequency is softened at the Brillouin zone boundaries of crystalline GaAs; (b) at the surface, the Ga-As bond is stronger than Ga-Te bond; and (c) the requirement that the final bond orientation of the Te surfactant should be rotated by 90degrees with respect to its initial orientation, we carried out a model study of an exchange process in epitaxial growth of GaAs (100). Even with very restrictive conditions imposed on the atomic movements, this study explains why Te is an effective surfactant for this type of growth. (C) 2002 Elsevier Science B.V. All rights reserved.Item Open Access Nanocrystal hybridized white light sources integrated on near UV leds(World Scientific Publishing, 2007) Nizamoğlu, Sedat; Demir, Hilmi VolkanWe report on CdSe/ZnS core-shell nanocrystal (NC) based white light sources integrated on near-UV InGaN/GaN light emitting diodes (LEDs). We present the design, epitaxial growth, fabrication, integration and characterization of such hybrid NC-LEDs that incorporate the dual combinations of cyan and yellow nanocrystals (λPL=500-580 nm) and the trio combinations of cyan, green, and red nanocrystals (λPL=500-540-620 nm).Item Open Access Near-UV InGaN/GaN-based dual-operation quantum optoelectronic devices(SPIE, 2007) Özel, Tuncay; Sarı, Emra; Nizamoğlu, Sedat; Demir, Hilmi VolkanWe present a novel dual-operation InGaN/GaN based quantum optoelectronic device (QOD) that operates as a quantum electroabsorption modulator in reverse bias and as a light emitter in forward bias in the spectral range of near-ultraviolet (UV). Here we report the design, epitaxial growth, fabrication, and characterization of such QODs that incorporate ∼2-3 nm thick InGaN/GaN quantum structures for operation between 380 nm and 400 nm. In reverse bias, our QODs show an optical absorption coefficient change of ∼14000 cm -1 with a reverse bias of 9 V (corresponding to ∼40 cm -1 absorption coefficient change for 1 V/μm field swing) at 385 nm, reported for the first time for InGaN/GaN quantum structures in the near-UV range. In forward bias, though, our QODs exhibit optical electroluminescence spectrum centered around 383 nm with a full width at half maximum of 20 nm and photoluminescence spectrum centered around 370 nm with a full width at half maximum of 12 nm. This dual operation makes such quantum optoelectronic devices find a wide range of optoelectronics applications both as an electroabsorption modulator and a light emitting diode (LED).Item Open Access Resonance broadening and tuning of split ring resonators by top-gated epitaxial graphene on SiC substrate(AIP Publishing LLC, 2013) Cakmakyapan, S.; Sahin, L.; Pierini, F.; Strupinski, W.; Özbay, EkmelSplit ring resonators (SRRs) are subwavelength structures that are able to localize and enhance the electromagnetic wave. Controlling the plasmonic resonance behavior of metallic nanostructures, such as SRRs, plays an important role in optoelectronics and nanophotonics applications. Electrically tunable carrier concentration of graphene provides hybrid devices, where the plasmonic structures and graphene are combined. In this paper, we report the design, fabrication, and measurement of a device comprising a SRR array on epitaxial graphene. We obtained resonance broadening and tuning of split ring resonators by utilizing an epitaxial graphene transistor with transparent top-gate.Item Open Access Silicon-Germanium multi-quantum well photodetectors in the near infrared(Optical Society of American (OSA), 2012) Onaran, E.; Onbasli, M. C.; Yesilyurt, A.; Yu, H. Y.; Nayfeh, A. M.; Okyay, Ali KemalSingle crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ∼10 mA/cm2 and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage. © 2012 Optical Society of America.Item Open Access A theoretical model for the epitaxial growth of Si(100) surface(Bilkent University, 2000) Dağ, SefaIn this thesis, we investigated atomic scale mechanisms of growth on the Si(lOO) surface. First principles quantum molecular dynamics calculations are performed, where self-consistent field electronic structure calculations within the density functional theory, and ionic relaxations carried out concomitantly. By using this method, we first determined the binding energy and binding sites of adatoms and ad-dimers. In the second stage, we simulated different configuration of dimer construction. In the third stage, we analyzed temperature dependent behaviour of dimers and we investigated translational and rotational motion of dimers. Finally, we presented a new theoretical model for ID epitaxial growth.