bluuebunny/crossref_metadata_2025_split huggingface dataset:
Voids in Hydrogenated Amorphous Silicon: A Comparison of ab initio Simulations and Proton NMR Studies
Authors: Chakraborty Sudeshna , Bobela David C , Taylor P C , Drabold D. A. 
Published: April 2011

ABSTRACTRecently, a new hydrogen NMR signal has been observed in a number of PECVD prepared hydrogenated amorphous silicon (a-Si:H) films of varying quality. It is speculated that the signal is the consequence of a dipolar-coupled hydrogen pair separated, on average, by 1.8 ± 0.1 Å. To elucidate the possible bonding configurations responsible for the NMR data of ref. [1], we have used ab initio simulation methods to determine a set of relaxed structures of a-Si:H with varying void sizes and H-concentrations. Models containing two isolated hydrogen atoms indicate a preferred H-H distance of approximately 1.8 Å when the two atoms bond to nearest neighbor silicon atoms. This separation also occurs for models containing small, hydrogenated voids, but the configurations giving rise to this H-H distance do not appear to be unique. For larger voids, a proton separation of about 2.4Å is seen, as noted previously [2]. There appears to be consistency between the computed structures and the NMR data for configurations consisting of isolated hydrogen pairs or for clusters of an even number of hydrogen atoms with the constraint that the average H-H distance is 1.8 Å. In this paper, we will discuss the most probable bonding configurations of clustered hydrogen based upon the extent of the NMR data and simulated structures.
Study of Large Area a-Si:H and nc-Si:H Based Multijunction Solar Cells and Materials
Authors: Xu Xixiang , Yan Baojie , Beglau Dave , Li Yang , DeMaggio Greg , Yue Guozhen , Banerjee Arindam , Yang Jeff , Guha Subhendu , Hugger Peter G. , Cohen J. David 
Published: April 2011

ABSTRACTSolar cells based on hydrogenated nanocrystalline silicon (nc-Si:H) have demonstrated significant improvement in the last few years. From the standpoint of commercial viability, good quality nc-Si:H films must be deposited at a high rate. In this paper, we present the results of our investigations on obtaining high quality nc-Si:H and a-Si:H films and solar cells over large areas using high deposition rate. We have employed the modified very high frequency (MVHF) glow discharge technique to realize high-rate deposition. Modeling studies were conducted to attain good spatial uniformity of electric field over a large area (15”×1”) MVHF cathode for nc-Si:H deposition. A comparative study has been carried out between the RF and MVHF plasma deposited a-Si:H and nc-Si:H single-junction and a-Si:H/nc-Si:H double-junction solar cells. By optimizing the nc-Si:H cell and the tunnel/recombination junctions, we have obtained an initial aperture-area (460 cm2) efficiency of 11.9% for a-Si:H/nc-Si:H double-junction cells using conventional RF (13.56 MHz) plasma deposition. The deposition rate was 3 Å/sec. Results on solar cells made with MVHF will also be presented.
The Effect of Electrical Stress on the New Top Gate N-type Depletion Mode Polycrystalline Thin Film Transistors Fabricated by Alternating Magnetic Field Enhanced Rapid Thermal Annealing
Authors: Lee Won-Kyu , Han Sang-Myeon , Park Sang-Geun , Choi Sung-Hwan , Choi Joonhoo , Han Min-Koo 
Published: April 2011

ABSTRACTWe have fabricated the new top gate depletion mode n-type alternating magnetic field enhanced rapid thermal annealing (AMFERTA) polycrystalline silicon (poly-Si) thin film transistors (TFTs), which show the excellent electrical characteristics and superior stability compared with hydrogenated amorphous silicon (a-Si:H) TFTs and excimer laser crystallized (ELC) low temperature polycrystalline silicon (LTPS) TFTs. The fabricated AMFERTA poly-Si TFTs were not degraded under hot-carrier stress, and highly biased vertical field stress. The considerably large threshold voltage shift (ΔVTH) and trap state density reducing were occurred when the gate bias and drain bias were both large enough. The dominant mechanism of instability in the fabricated depletion mode AMFERTA poly-Si TFTs may be due to carrier induced donor-like defects reduction within the channel layer, especially near the drain junction.
Negative Bias Temperature Instability for P-channel of LTPS Thin Film Transistors with Fluorine Implantation
Authors: Kao Chyuan-Haur , Sung W. H. 
Published: April 2011

ABSTRACTThis paper studies the impact of LTPS (low temperature polycrystalline silicon) TFTs with fluorine implantation under NBTI (Negative bias temperature instability) stress. The fluorinated TFTs' devices can obtain better characteristics with samller threshold voltage shift, lower trap states and lower subthreshold swing variation. Therefore, the fluorine implantation does not only improve initial electrical characteristics, but also suppresses the NBTI-induced degradation.
Noise Analysis of Image Sensor Arrays for Large-Area Biomedical Imaging
Authors: Lai Jackson , Striakhilev Denis , Vygranenko Yuri , Heiler Gregory , Nathan Arokia , Tredwell Timothy 
Published: April 2011

ABSTRACTLarge area digital imaging made possible by amorphous silicon thin-film transistor (a-Si TFT) technology, coupled with a-Si photo-sensors, provides an excellent readout platform to form an integrated medical image capture system. Major development challenges evolve around optimization of pixel architecture for detector fill factor, and manufacturability, while suppressing noise stemming from pixel array and external electronics. This work discusses the behavior and modeling of system noise that arises from imaging array operations. An active pixel sensor (APS) design with on-pixel amplification is studied. Our evaluation demonstrates that a 17 inch by 17 inch array can achieve system noise as low as 1000 electrons through proper design and optimization.
Fluorescence Detection of DNA Hybridization Using an Integrated Thin-Film Amorphous Silicon n-i-p Photodiode
Authors: Pimentel Alexandra , Cabeça R. , Rodrigues M. , Prazeres D.M.F. , Chu V. , Conde J. P. 
Published: April 2011

ABSTRACTThis paper presents the fluorescence detection of DNA hybridization with a surface immobilized probe using an hydrogenated amorphous silicon photosensor. This sensor integrates a SiO2 layer for DNA probe immobilization, a p-i-n amorphous silicon (a-Si:H) photodiode for fluorescence detection and a fluorescence filter of amorphous silicon carbon (a-SiC:H) to cut the excitation light. With this integrated photosensor system, a five order of magnitude difference was obtained in the signal measured at the emission wavelength and that measured at the excitation wavelength for the same incident photon flux. The fluorophore Alexa Fluor 430 was used to label the DNA target molecules and a laser at 405 nm and a photon flux of 5.7×1016 cm−2.s−1 was used as the excitation light source. The detection limit achieved for fluorophores in solution in contact with the device and for fluorophores immobilized on the device surface is 5×10−9 M and 0.4 pmol/cm2, respectively. The fluorescence detection of the DNA target hybridization with a covalently or electrostatically immobilized probe was successfully detected at a surface density of ∼3 pmol/cm2.
Noise Characterization of Polycrystalline Silicon Thin Film Transistors for X-ray Imagers Based on Active Pixel Architectures
Authors: Antonuk L. E. , Koniczek M. , McDonald J. , El-Mohri Y. , Zhao Q. , Behravan M. 
Published: April 2011

ABSTRACTAn examination of the noise of polycrystalline silicon thin film transistors, in the context of flat panel x-ray imager development, is reported. The study was conducted in the spirit of exploring how the 1/f, shot and thermal noise components of poly-Si TFTs, determined from current noise power spectral density measurements, as well as through calculation, can be used to assist in the development of imagers incorporating pixel amplification circuits based on such transistors.
1T Memory Cell Based on PVDF-TrFE Field Effect Transistor
Authors: Salvatore Giovanni Antonio , Bouvet Didier , Ionescu Mihai Adrian , Riester Sebastian , Stolichnov Igor , Gysel Roman , Setter Nava 
Published: April 2011

ABSTRACTInterest in PVDF-TrFE copolymers as ferroelectric material for Memory application is driven by the prospect of having low cost, low operating voltage and fully organic device. Some previous studies reported FET designs using copolymers [refs 1,2] but none of these structures were fully integrated on silicon wafers and using a MOSFET fabrication process. We present for the first time the integration of a PVDF-TrFE (70%-30%) layer into a standard n-MOS transistor through a quasi-standard semiconductor technology. This allows us to achieve a Non Volatile Memory cell and at the same time to compact capacitor-transistor ferroelectric cell into a one-transistor memory cell.
High-resolution Photoinduced Transient Spectroscopy of Defect Centers in Undoped Semi-Insulating 6H-SiC
Authors: Kaminski Pawel , Kozlowski Roman , Miczuga Marcin , Pawlowski Michal , Kozubal Michal , Zelazko Jaroslaw 
Published: April 2011

ABSTRACTHigh-resolution photoinduced transient spectroscopy (HRPITS) has been applied to studying defect centers controlling the charge compensation in semi-insulating (SI), vanadium-free, bulk 6H- SiC. The photocurrent relaxation waveforms were digitally recorded in the temperature range of 50 − 750 K and a new approach to extract the parameters of defect centers from the temperature-induced changes in the time constants of the waveforms has been implemented. It is based on a two-dimensional analysis using the numerical inversion of the Laplace transform. As a result, the images of spectral fringes depicting the temperature dependences of the emission rate of charge carriers for defect centers are created. Using the new procedure for the analysis of the photocurrent relaxation waveforms and the new way of the visualization of the thermal emission rate dependences, a number of shallow and deep defect levels ranging from 80 to 1900 meV have been detected. The obtained results indicate that defect structure of undoped SI bulk 6H-SiC is very complex and the material properties are affected by various point defects occupying the hexagonal and quasi-cubic lattice sites.
Point Defects in SiC
Authors: Gali Ádám , Bockstedte Michel , Son Ngyen Tien , Janzén Erik 
Published: April 2011

ABSTRACTTight control of defects is pivotal for semiconductor technology. However, even the basic defects are not entirely understood in silicon carbide. In the recent years significant advances have been reached in identification of defects by combining the experimental tools like electron paramagnetic resonance and photoluminescence with ab initio calculations. We summarize these results and their consequences in silicon carbide based technology. We show recent methodological developments making possible the accurate calculation of absorption and emission signals of defects.
Improved SiC Epitaxial Material for Bipolar Applications
Authors: Bergman Peder , Hassan Jawad ul , Ellison Alex , Henry Anne , Godignon Philippe , Brosselard Pierre , Janzén Erik 
Published: April 2011

ABSTRACTEpitaxial growth on Si-face nominally on-axis 4H-SiC substrates has been performed using horizontal Hot-wall chemical vapor deposition system. The formation of 3C inclusions is one of the main problem with growth on on-axis Si-face substrates. In situ surface preparation, starting growth parameters and growth temperature are found to play a vital role in the epilayer polytype stability. High quality epilayers with 100% 4H-SiC were obtained on full 2″ substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be eliminated through growth on on-axis substrates. Also, no other kind of structural defects were found in the grown epilayers. These layers have also been processed for simple PiN structures to observe any bipolar degradation. More than 70% of the diodes showed no forward voltage drift during 30 min operation at 100 A/cm2.
Deep-Level Defects in Nitrogen-Doped 6H-SiC Grown by PVT Method
Authors: Kaminski Pawel , Kozubal Michal , Grasza Krzysztof , Tymicki Emil 
Published: April 2011

ABSTRACTAn effect of the nitrogen concentration on the concentrations of deep-level defects in bulk 6H-SiC single crystals is investigated. Six electron traps labeled as T1A, T1B, T2, T3, T4 and T5 with activation energies of 0.34, 0.40, 0.64, 0.67, 0.69, and 1.53 eV, respectively, were revealed. The traps T1A (0.34 eV) and T1B (0.40 eV), observed in the samples with the nitrogen concentration ranging from ∼2×1017 to 5×1017 cm−3, are attributed to complexes formed by carbon vacancies located at various lattice sites and carbon antisites. The concentrations of traps T2 (0.64 eV) and T3 (0.67 eV) have been found to rise from ∼5×1015 to ∼1×1017 cm−3 with increasing the nitrogen concentration from ∼2×1017 to ∼2.0×1018 cm−3. These traps are assigned to complexes involving silicon vacancies occupying hexagonal and quasi-cubic sites, respectively, and nitrogen atoms. The trap T4 (0.69 eV) concentration also substantially rises with increasing the nitrogen concentration and it is likely to be related to complexes formed by carbon antisites and nitrogen atoms. The midgap trap T5 (1.53 eV) is presumably associated with vanadium contamination. The presented results show that doping with nitrogen involves a significant change in the defect structure of 6H-SiC single crystals.
High-frequency electron paramagnetic resonance study of the as deposited and annealed carbon-rich hydrogenated amorphous silicon-carbon films
Authors: Vasin A. V. , Kalabukhova E. N. , Lukin S. N. , Savchenko D. V. , Lysenko V. S. , Nazarov A. N. , Rusavsky A. V. , Koshka Y. 
Published: April 2011

ABSTRACTThree paramagnetic defects were revealed in amorphous hydrogenated carbon-rich silicon-carbon alloy films (a-SiC:H), which were attributed to the to silicon (Si) dangling bonds (Si DB), carbon-related defects (CRD), and bulk Si DB defect bonded with nitrogen atoms Si-N2Si. The effect of thermal annealing on a-SiC:H films was studied. It was established that annealing at high temperatures leads to formation of graphite-like carbon clusters in a-SiC:H films and strong increase of the concentration of CRD, while EPR signal from Si DB disappeared. A dependence of the resonance positions for both Si DB and CRD signals on the orientation of the magnetic field relative to the a-SiC:H film plane was found at Q-band and D-band frequencies and was explained by the influence of demagnetizing fields, which is becoming significant at high spin density of the paramagnetic centers, higher microwave frequency, and low temperature. A demagnetizing field of 11 Gs was found in annealed a-SiC:H film at 140 GHz and 4.2 K.
Impact Ionization in Ion Implanted 4H-SiC Photodiodes
Authors: Loh Wei Sun , Goh Eric Z. J. , Vassilevski Konstantin , Nikitina Irina , David John P. R. , Wright Nick G , Johnson C Mark 
Published: April 2011

ABSTRACTHole dominated avalanche multiplication and thus breakdown characteristics of ion implanted 4H-SiC p+-n−-n+ photodiodes were determined by means of photomultiplication measurements using 325 nm UV light. All the tested diodes exhibited low reverse leakage current and reasonably uniform avalanche breakdown. With avalanche widths of 0.2 µm to 1.5 µm and the capability to measure multiplication factor as low as 1.001, the room temperature impact ionization coefficients were precisely deduced from these 4H-SiC diodes using a local ionization model for electric fields ranging from 1.25 MV/cm to 2.8 MV/cm. The results agree with those reported by Ng et al. and are within the accuracy of both the C-V measurements and electric-field determinations.
Spontaneous and Piezoelectric Polarization Effects on the Frequency Response of Wurtzite Aluminium Gallium Nitride / Silicon Carbide Heterojunction Bipolar Transistors
Authors: Praharaj Choudhury 
Published: April 2011

ABSTRACTWe present theoretical calculations for the effect of spontaneous and piezoelectric polarization on the base resistance and frequency response of wurtzite Aluminium Gallium Nitride / Silicon Carbide Heterojunction Bipolar Transistors. Heterojunction Bipolar Transistors ( HBTs ) built using wide band gap semiconductors with AlGaN emitter and SiC base/collector hold the promise of high-power and high-frequency operation due to lower impact ionization coefficients and higher breakdown voltages. Further, Silicon Carbide has an indirect bang gap, and a large lifetime of minority carriers compared to most other compound semiconductors, which tend to have direct band gaps. This reduces the base recombination factor when the base is made from SiC, and helps to achieve higher overall current gain. Spontaneous and piezoelectric polarizations of the order of 1013 electrons per cm2 exist in wurtzite wide band-gap semiconductors. This has a non-trivial effect on band profile, charge transport and overall device characteristics since the polarization-induced charges are of the same order of magnitude as the total dopant charge content of critical device layers, and can significantly affect the amount of mobile charge depletion or accumulation in these layers. We calculate the effect of this polarization for both very thin pseudomorphic emitters and for relaxed emitter structures. We present calculations for the cases of Si-face and C-face SiC, since the signs of polarization-induced charges are different for the two cases. The intrinsic base resistance near emitter flat-band conditions is changed by a factor of 10 depending on the alloy composition of the emitter and the polarity of growth. The maximum frequency of oscillation under emitter flat-band conditions can also be modulated by the polarization-induced charges by up to 60%. Our calculations show that the technologically less prevalent C-face SiC can give a higher advantage for frequency response, especially when the emitter thickness is larger than the critical thickness.
Characterization and Growth Mechanism of B12As2 Epitaxial Layers Grown on (1-100) 15R-SiC
Authors: Chen Hui , Wang Guan , Dudley Michael , Xu Zhou , Edgar James. H. , Batten Tim , Kuball Martin , Zhang Lihua , Zhu Yimei 
Published: April 2011

ABSTRACTA systematic study is presented of the heteroepitaxial growth of B12As2 on m-plane 15R-SiC. In contrast to previous studies of B12As2 on other substrates, including (100) Si, (110) Si, (111) Si and (0001) 6H-SiC, single crystalline and untwinned B12As2 was achieved on m-plane 15R-SiC. Observations of IBA on m-plane (1100)15R-SiC by synchrotron white beam x-ray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM) confirm the good quality of the films on the 15R-SiC substrates. The growth mechanism of IBA on m-plane 15R-SiC is discussed. This work demonstrates that m-plane 15R-SiC is potentially a good substrate choice to grow high quality B12As2 epilayers.
Long-Term Characterization of 6H-SiC Transistor Integrated Circuit Technology Operating at 500 °C
Authors: Neudeck Philip , Spry David J. , Chen Liang-Yu , Chang Carl W. , Beheim Glenn M. , Okojie Robert S. , Evans Laura J. , Meredith Roger D. , Ferrier Terry L. , Krasowski Michael J. , Prokop Norman F. 
Published: April 2011

ABSTRACTNASA has been developing very high temperature semiconductor integrated circuits for use in the hot sections of aircraft engines and for Venus exploration. This paper reports on long-term 500 °C electrical operation of prototype 6H-SiC integrated circuits based on epitaxial 6H-SiC junction field effect transistors (JFETs). As of this writing, some devices have surpassed 4000 hours of continuous 500 °C electrical operation in oxidizing air atmosphere with minimal change in relevant electrical parameters.
3D Thermal Stress Models for Single Chip SiC Power Sub-Modules
Authors: Tsao Bang-Hung , Lawson Jacob , Scofield James 
Published: April 2011

ABSTRACTThree dimensional models of single chip SiC power sub-modules were generated using ANSYS in order to simulate the effects of various substrate materials, heat fluxes, and heat transfer coefficients on temperature and thermal stress contours. Silicon nitride, aluminum-nitride, alumina were compared as substrates with or without an additional layer of CVD diamond on either top or bottom of the surfaces. Simulated heat fluxes of 100 to 300 watts/cm2 resulted in device junction temperatures in the range of 377 to 535 K. With modest cooling, represented by a heat transfer coefficient (hconv) of 3350 watts/m2 K, SiC chips operated at 300 watts/cm2 power density maintained junction temperatures Tj < 535 K. Both the maximum and minimum chip temperature decreased with increasing heat transfer coefficient from 50 to 5000 watts/m2 K. In the applied heat flux range, the minimum and maximum Von Mises stress of a simulated single SiC device sub-module was between 946 MPa to 1.31GPa. If consistent with simulation results, CVD diamond integrated substrates should be superior to those comprised of only AlN, Al2O3, and Si3N4. Experimental validation of ANSYS results and more extensive multiple-chip power module simulations will also be explored.
Micro-uniformity during laser anneal : metrology and physics
Authors: Vandervorst W. , Rosseel E. , Lin R. , Petersen D. H. , Clarysse T. , Goossens J. , Nielsen P. F. , Churton K. 
Published: April 2011

ABSTRACTMaintaining or improving device performance while scaling semiconductor devices, necessitates the development of extremely shallow (< 20 nm) source/drain extensions with a very high dopant concentration and electrical activation level. Whereas solutions based on RTA with cocktail implants have been proposed in previous generations, sub-45 nm technologies will require even shallower junctions which motivates the research effort on milli-second anneal approaches as these hold the promise of minimal diffusion coupled with high activation levels [1]. Laser annealing is one of these concepts proposed to achieve the junction specifications and is typically described as a msec anneal process. Different from lamp based concepts which illuminate a full wafer simultaneously, the laser has an illuminated area which is much smaller than the wafer size thus necessitating a dedicated scanning pattern. In such a case one is potentially faced with areas subject to multiple overlaps and/or different temperatures and thus issues related to within wafer and within die uniformity need to be addressed.In this work we use optimized metrology to probe such macro- and micro non-uniformity and determine the origin of the various components contributing to the observed non-uniformity patterns (laser stitching patterns, laser beam uniformity, optical path) and their impact on the local sheet resistance.
USJ Dopant Bleaching and Device Effects in Advanced Microelectronic Plasma Enhanced Resist Strip Processing
Authors: Wirbeleit Frank , Grimm Volker , Krüger Christian , Streck Christoph , Sonnemans Roger , Berry Ivan 
Published: April 2011

ABSTRACTThe impact of low temperature plasma resist strip on doped silicon surface and microelectronic device performance is investigated using different chemical gas mixtures. In this investigation, different plasma treatments where applied on non-structured and structured silicon on insulator (SOI) wafers post ultra shallow surface implants .The main surface impacts dopant bleaching and oxide loss in conjunction with plasma enhanced re-oxidation are analyzed by time of flight secondary ion mass spectrometry (TOF-SIMS) and electrical measurements of microelectronic test devices. As the result, a long range plasma radiation induced dopant activation and deactivation is separated as the main effect from surface oxide loss and re-oxidation processes. This implies further optimization of plasma resist strip processes for device improvements.