Browsing by Subject "Semiconducting silicon compounds"

Now showing 1 - 14 of 14

Open Access
Chemically specific dynamic characterization of photovoltaic and photoconductivity effects of surface nanostructures
(American Chemical Society, 2010) Ekiz, O. Ö.; Mizrak, K.; Dâna, A.
We report characterization of photovoltaic and photoconductivity effects on nanostructured surfaces through light induced changes in the X-ray photoelectron spectra (XPS). The technique combines the chemical specificity of XPS and the power of surface photovoltage spectroscopy (SPV), with the addition of the ability to characterize photoconductivity under both static and dynamic optical excitation. A theoretical model that quantitatively describes the features of the observed spectra is presented. We demonstrate the applicability of the model on a multitude of sample systems, including homo- and heterojunction solar cells, CdS nanoparticles on metallic or semiconducting substrates, and carbon nanotube films on silicon substrates.
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.
Open Access
Experimental and theoretical investigations of electronic and atomic structure of Si-nanocrystals formed in sapphire by ion implantation
(IOP, 2008) Wainstein, D.; Kovalev, A.; Tetelbaum, D.; Mikhailov, A.; Bulutay, Ceyhun; Aydınlı, Atilla
The semiconductor nanocomposites based on Si nanocrystals in dielectric matrices attract a great amount of attention due to their ability for luminescence in visible and near-IR part of the electromagnetic spectrum. Si nanocrystals in sapphire matrix were formed by Si+ ion implantation with doses from 5×1016 to 3×1017 cm -2 at an accelerating voltage 100 kV and post-implantation annealing at 500-1100 d̀C for 2 hours. Depth distribution of lattice defects, impurities and Si nanocrystals, the peculiarities of interband electronic transitions were investigated by XPS and HREELS. The molecular orbitals and local electronic structure of the Al2O3 matrix with Si nanocrystals was calculated using an atomistic pseudopotential technique. The electronic structure of Si nanocrystals as determined from HREELS measurements is in good agreement with the theoretically calculated electronic structure for Si nanocrystals.
Open Access
Germanium for high performance MOSFETs and optical interconnects
(2008-10) Saraswat, K. C.; Kim, D.; Krishnamohan, T.; Kuzum, D.; Okyay, Ali Kemal; Pethe, A.; Yu H.-Y.
It is believed that to continue the scaling of silicon CMOS innovative device structures and new materials have to be created in order to continue the historic progress in information processing and transmission. Recently germanium has emerged as a viable candidate to augment Si for CMOS and optoelectronic applications. In this work we will first review recent results on growth of thin and thick films of Ge on Si, technology for appropriate cleaning of Ge, surface passivation using high-κ dielectrics, and metal induced crystallization of amorphous Ge and dopant activation. Next we will review application of Ge for high performance MOSFETs. Innovative Si/Ge MOS heterostructures will be described with high on current and low off currents. Finally we will describe optical detectors and modulators for on-chip and off-chip interconnect. Successful integration of Ge on Si should allow continued scaling of silicon CMOS to below 22 nm node. ©The Electrochemical Society.
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.
Open Access
Imaging capability of pseudomorphic high electron mobility transistors, AlGaN/GaN, and Si micro-Hall probes for scanning Hall probe microscopy between 25 and 125 °c
(American Vacuum Society, 2009) Akram, R.; Dede, M.; Oral, A.
The authors present a comparative study on imaging capabilities of three different micro-Hall probe sensors fabricated from narrow and wide band gap semiconductors for scanning hall probe microscopy at variable temperatures. A novel method of quartz tuning fork atomic force microscopy feedback has been used which provides extremely simple operation in atmospheric pressures, high-vacuum, and variable-temperature environments and enables very high magnetic and reasonable topographic resolution to be achieved simultaneously. Micro-Hall probes were produced using optical lithography and reactive ion etching process. The active area of all different types of Hall probes were 1×1 μ m2. Electrical and magnetic characteristics show Hall coefficient, carrier concentration, and series resistance of the hall sensors to be 10 mG, 6.3× 1012 cm-2, and 12 k at 25 °C and 7 mG, 8.9× 1012 cm-2 and 24 k at 125 °C for AlGaNGaN two-dimensional electron gas (2DEG), 0.281 mG, 2.2× 1014 cm-2, and 139 k at 25 °C and 0.418 mG, 1.5× 1014 cm-2 and 155 k at 100 °C for Si and 5-10 mG, 6.25× 1012 cm-2, and 12 k at 25 °C for pseudomorphic high electron mobility transistors (PHEMT) 2DEG Hall probe. Scan of magnetic field and topography of hard disc sample at variable temperatures using all three kinds of probes are presented. The best low noise image was achieved at temperatures of 25, 100, and 125 °C for PHEMT, Si, and AlGaNGaN Hall probes, respectively. This upper limit on the working temperature can be associated with their band gaps and noise associated with thermal activation of carriers at high temperatures.
Open Access
Matrix density effect on morphology of germanium nanocrystals embedded in silicon dioxide thin films
(Materials Research Society, 2011) Alagoz, A. S.; Genisel, M. F.; Foss, Steinar; Finstad, T. G.; Turan, R.
Flash type electronic memories are the preferred format in code storage at complex programs running on fast processors and larger media files in portable electronics due to fast write/read operations, long rewrite life, high density and low cost of fabrication. Scaling limitations of top-down fabrication approaches can be overcome in next generation flash memories by replacing continuous floating gate with array of nanocrystals. Germanium (Ge) is a good candidate for nanocrystal based flash memories due its small band gap. In this work, we present effect of silicon dioxide (SiO 2) host matrix density on Ge nanocrystals morphology. Low density Ge+SiO 2 layers are deposited between high density SiO 2 layers by using off-angle magnetron sputter deposition. After high temperature post-annealing, faceted and elongated Ge nanocrystals formation is observed in low density layers. Effects of Ge concentration and annealing temperature on nanocrystal morphology and mean size were investigated by using transmission electron microscopy. Positive correlation between stress development and nanocrystal size is observed at Raman spectroscopy measurements. We concluded that non-uniform stress distribution on nanocrystals during growth is responsible from faceted and elongated nanocrystal morphology.
Open Access
Methods for probing charging properties of polymeric materials using XPS
(2010) Sezen, H.; Ertas, G.; Süzer, Şefik
Various thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to ±10 V d.c. bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 MΩ resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift due to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger Reff, and conversely the PMMA component shifts are smaller due to the presence of PS domains.
Open Access
Optically implemented broadband blueshift switch in the terahertz regime
(American Physical Society, 2011-01-18) Shen, N. H.; Massaouti, M.; Gokkavas, M.; Manceau J. M.; Özbay, Ekmel; Kafesaki, M.; Koschny, T.; Tzortzakis, S.; Soukoulis, C. M.
We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime.
Open Access
Plasmonic gratings for enhanced near infrared sensitivity of Silicon based Schottky photodetectors
(IEEE, 2011) Polat, Kazım Gürkan; Aygun, Levent Erdal; Okyay, Ali Kemal
Schottky photodetectors have been intensively investigated due to their high speeds, low device capacitances, and sensitivity in telecommunication standard bands, in the 0.8μm to 1.5μm wavelength range. Due to extreme cost advantage of Silicon over compound semiconductors, and seamless integration with VLSI circuits, metal-Silicon Schottky photodetectors are attractive low cost alternatives to InGaAs technology. However, efficiencies of Schottky type photodetectors are limited due to thin absorption region. Previous efforts such as resonant cavities increase the sensitivity using optical techniques, however their integration with VLSI circuits is difficult. Therefore, there is a need for increasing Schottky detector sensitivity, in a VLSI compatible fashion. To address this problem, we design plasmonic grating structures to increase light absorption at the metal-Silicon Schottky interface. There are earlier reports of plasmonic structures to increase Schottky photodetector sensitivity, with a renowned interest in the utilization of plasmonic effects to improve the absorption characteristics of metal-semiconductor interfaces. In this work, we report the design, fabrication and characterization of Gold-Silicon Schottky photodetectors with enhanced absorption in the near infrared region. © 2011 IEEE.
Open Access
Response of polyelectrolyte layers to the SiO2 substrate charging as probed by XPS
(2009) Conger, C. P.; Süzer, Şefik
A single layer of the Cationic polyelectrolyte poly(allyamine) hydrochloride (PAH) deposited, using the layer-by-layer technique, on a silicon substrate containing 5 nm oxide layer is investigated by XPS while applying an external potential bias to the sample to control and manipulate the charge built-up on the oxide layer. Under application of a -10 V bias, the oxide layer is positively charged due to Photoemission process, evidenced by the measured Si2p binding energy of 104.4 eV. Application of a +10 V bias attracts the low energy neutralizing electrons, stemming from a hot filament, and leads to a negatively charged oxide layer, also evidenced by the measured Si2p binding energy of 102.9 eV. The single polyelectrolyte overlayer also responds to this polarity change of the oxide layer underneath by displaying a somewhat larger shifts both in the C1s and Nls peaks. In addition to the shifts in the positions, the N1s peaks undergo a significant intensity depletion, mostly on the positively charged -N+ component. We interpret this intensity depletion to be the result of reorientation of some of the dangling positively charged groups by moving toward the negatively charged oxide underlayer. To our knowledge this is the first time that a chemically specific response to an electrical stimuli is reported using XPS. A bilayer LbL film consisting of PAH and PSS, exhibits even a larger charging shift, but this time no intensity alteration is observed, most probably due to locking of the -N+ groups by the -SO3 + counterions of the second layer. © 2009 American Chemical Society.
Open Access
Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition
(2012) Ozgit, C.; Donmez I.; Alevli, M.; Bıyıklı, Necmi
We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3). At 185 °C, deposition rate saturated for TMA and NH 3 doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH 3 resulted in a constant growth rate of ∼ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≤ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ∼ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum. © 2011 Elsevier B.V. All rights reserved.
Open Access
Ta/Si Schottky diodes fabricated by magnetron sputtering technique
(2010) Ocak, Y.S.; Genisel, M.F.; Kiliçoǧlu, T.
Electrical properties of Ta/n-Si and Ta/p-Si Schottky barrier diodes obtained by sputtering of tantalum (Ta) metal on semiconductors have been investigated. The characteristic parameters of these contacts like barrier height, ideality factor and series resistance have been calculated using current voltage (I-V) measurements. It has seen that the diodes have ideality factors more than unity and the sum of their barrier heights is 1.21 eV which is higher than the band gap of the silicon (1.12 eV). The results have been attributed the effects of inhomogeneities at the interface of the devices and native oxide layer. In addition, the barrier height values determined using capacitance-voltage (C-V) measurements have been compared the ones obtained from I-V measurements. It has seen that the interface states have strong effects on electrical properties of the diodes such as C-V and Rs-V measurements. © 2010 Elsevier Ltd. All rights reserved.
Open Access
Wafer bonded capacitive micromachined underwater transducers
(IEEE, 2009-09) Olcum, Selim; Oǧuz, Kaan; Şenlik, Muhammed N.; Yamaner F. Y.; Bozkurt, A.; Atalar, Abdullah; Köymen, Hayrettin
In this work we have designed, fabricated and tested CMUTs as underwater transducers. Single CMUT membranes with three different radii and 380 microns of thickness are fabricated for the demonstration of an underwater CMUT element. The active area of the transducer is fabricated on top of a 3″ silicon wafer. The silicon wafer is bonded to a gold electrode coated glass substrate wafer 10 cm in diameter. Thermally grown silicon oxide layer is used as the insulation layer between membrane and substrate electrodes. Electrical contacts and insulation are made by epoxy layers. Single CMUT elements are tested in air and in water. Approximately 40% bandwidth is achieved around 25 KHz with a single underwater CMUT cell. Radiated pressure field due to second harmonic generation when the CMUTs are driven with high sinusoidal voltages is measured. ©2009 IEEE.