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Arokia Nathan - One of the best experts on this subject based on the ideXlab platform.
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non ohmic contact resistance and field effect mobility in Nanocrystalline Silicon thin film transistors
Applied Physics Letters, 2008Co-Authors: Arman Ahnood, Arokia Nathan, Khashayar Ghaffarzadeh, Peyman Servati, Mohammad R Esmaeilirad, Andrei SazonovAbstract:Contact resistance has a significant impact on the electrical characteristics of thin film transistors. It limits their maximum on-current and affects their subsequent behavior with bias. This distorts the extracted device parameters, in particular, the field-effect mobility. This letter presents a method capable of accounting for both the non-ohmic (nonlinear) and ohmic (linear) contact resistance effects solely based upon terminal I-V measurements. Applying our analysis to a Nanocrystalline Silicon thin film transistor, we demonstrate that contact resistance effects can lead to a twofold underestimation of the field-effect mobility.
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Absence of defect state creation in Nanocrystalline Silicon thin film transistors deduced from constant current stress measurements
APPL PHYS LETT, 2007Co-Authors: Arokia NathanAbstract:The authors discuss time and temperature dependences of the shift in threshold voltage (Delta V-T) of Nanocrystalline Silicon (nc-Si) thin film transistors (TFTs) stressed at constant drain currents. In contrast to the behavior of the hydrogenated amorphous Silicon (a-Si:H) counterpart, a weak temperature dependence of Delta V-T was observed. The results follow the charge trapping model and the predicted stretched-exponential time dependence that saturates at prolonged stress times. In addition, Delta V-T does not fit into the thermalization energy concept that was developed based on the defect state creation model for a-Si:H TFTs. The results indicate absence of defect state creation in nc-Si TFTs.
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directly deposited Nanocrystalline Silicon thin film transistors with ultra high mobilities
Applied Physics Letters, 2006Co-Authors: Czangho Lee, Arokia Nathan, Andrei Sazonov, J RobertsonAbstract:The authors report ultrahigh mobility Nanocrystalline Silicon thin-film transistors directly deposited by radio-frequency plasma enhanced chemical vapor deposition at 150°C. The transistors show maximum effective field effect mobilities of 450cm2∕Vs for electrons and 100cm2∕Vs for holes at room temperature. The authors argue that the key factor in their results is the reduction of the oxygen content, which acts as an accidental donor.
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high mobility Nanocrystalline Silicon thin film transistors fabricated by plasma enhanced chemical vapor deposition
Applied Physics Letters, 2005Co-Authors: Andrei Sazonov, Arokia NathanAbstract:Hydrogenated Nanocrystalline Silicon (nc-Si:H) films were deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at 260°C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2). The high-quality nc-Si:H film showed an oxygen concentration (CO) of ∼1.5×1017at.∕cm3 and a dark conductivity (σd) of ∼10−6S∕cm, while the Raman crystalline volume fraction (Xc) was over 80%. Top-gate nc-Si:H thin-film transistors employing an optimized ∼100nm nc-Si:H channel layer exhibited a field-effect mobility (μFE) of ∼150cm2∕Vs, a threshold voltage (VT) of ∼2V, a subthreshold slope (S) of ∼0.25V∕dec, and an ON∕OFF current ratio of ∼106.
Andrei Sazonov - One of the best experts on this subject based on the ideXlab platform.
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non ohmic contact resistance and field effect mobility in Nanocrystalline Silicon thin film transistors
Applied Physics Letters, 2008Co-Authors: Arman Ahnood, Arokia Nathan, Khashayar Ghaffarzadeh, Peyman Servati, Mohammad R Esmaeilirad, Andrei SazonovAbstract:Contact resistance has a significant impact on the electrical characteristics of thin film transistors. It limits their maximum on-current and affects their subsequent behavior with bias. This distorts the extracted device parameters, in particular, the field-effect mobility. This letter presents a method capable of accounting for both the non-ohmic (nonlinear) and ohmic (linear) contact resistance effects solely based upon terminal I-V measurements. Applying our analysis to a Nanocrystalline Silicon thin film transistor, we demonstrate that contact resistance effects can lead to a twofold underestimation of the field-effect mobility.
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directly deposited Nanocrystalline Silicon thin film transistors with ultra high mobilities
Applied Physics Letters, 2006Co-Authors: Czangho Lee, Arokia Nathan, Andrei Sazonov, J RobertsonAbstract:The authors report ultrahigh mobility Nanocrystalline Silicon thin-film transistors directly deposited by radio-frequency plasma enhanced chemical vapor deposition at 150°C. The transistors show maximum effective field effect mobilities of 450cm2∕Vs for electrons and 100cm2∕Vs for holes at room temperature. The authors argue that the key factor in their results is the reduction of the oxygen content, which acts as an accidental donor.
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high mobility Nanocrystalline Silicon thin film transistors fabricated by plasma enhanced chemical vapor deposition
Applied Physics Letters, 2005Co-Authors: Andrei Sazonov, Arokia NathanAbstract:Hydrogenated Nanocrystalline Silicon (nc-Si:H) films were deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at 260°C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2). The high-quality nc-Si:H film showed an oxygen concentration (CO) of ∼1.5×1017at.∕cm3 and a dark conductivity (σd) of ∼10−6S∕cm, while the Raman crystalline volume fraction (Xc) was over 80%. Top-gate nc-Si:H thin-film transistors employing an optimized ∼100nm nc-Si:H channel layer exhibited a field-effect mobility (μFE) of ∼150cm2∕Vs, a threshold voltage (VT) of ∼2V, a subthreshold slope (S) of ∼0.25V∕dec, and an ON∕OFF current ratio of ∼106.
Subhendu Guha - One of the best experts on this subject based on the ideXlab platform.
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correlation of texture of ag zno back reflector and photocurrent in hydrogenated Nanocrystalline Silicon solar cells
Solar Energy Materials and Solar Cells, 2012Co-Authors: Baojie Yan, Guozhen Yue, Jeffrey Yang, Laura Sivec, Jessica Owensmawson, Subhendu GuhaAbstract:Abstract We studied the effect of Ag/ZnO back reflectors (BRs) with textured Ag and thin ZnO layers on hydrogenated Nanocrystalline Silicon (nc-Si:H) solar cell performance. We found that the photocurrent density increases with Ag texture when the surface root-mean-square (RMS) is smaller than 40 nm. The best Ag texture for nc-Si:H cells has an RMS ∼40 nm and lateral feature size ∼500 nm. Increasing the surface roughness further results in increased light scattering, but no additional gain in the photocurrent density is observed. Using the optimized BRs, we achieved a short circuit current density over 30 mA/cm 2 in nc-Si:H solar cells.
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optimization of back reflector for high efficiency hydrogenated Nanocrystalline Silicon solar cells
Applied Physics Letters, 2009Co-Authors: Guozhen Yue, Baojie Yan, Jessica M Owens, Jeffrey Yang, Laura Sivec, Subhendu GuhaAbstract:We have studied the effect of texture in Ag/ZnO back reflectors (BRs) on the performance of hydrogenated Nanocrystalline Silicon (nc-Si:H) solar cells. While a larger texture provides superior light trapping, it also deteriorates the nc-Si:H quality. We have used total and diffused reflection and atomic force microscopy to evaluate the BR texture. A BR with textured Ag and thin ZnO layers has been found to give the best cell performance. Using the optimized BR, we have achieved an initial active-area efficiency of 10.2% in a nc-Si:H single-junction cell and a stable total-area efficiency of 12.5% in a hydrogenated amorphous Silicon/nc-Si:H/nc-Si:H triple-junction cell.
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material structure and metastability of hydrogenated Nanocrystalline Silicon solar cells
Applied Physics Letters, 2006Co-Authors: Guozhen Yue, Baojie Yan, Jeffrey Yang, Subhendu Guha, Gautam Ganguly, Charles W TeplinAbstract:We find that the volume fraction of amorphous component in hydrogenated Nanocrystalline Silicon intrinsic layers is not necessarily the determining factor for the light-induced metastability ofn-i-p solar cells. Small grains and/or intermediate range order may play an important role in improving the stability. The distribution of nanocrystallites along the growth direction is also important. Based on the findings, we have optimized the hydrogen dilution profiling for controlling the structural evolution and have reduced the light-induced degradation of solar cells. As a result, we have achieved initial and stable active-area efficiencies of 14.1% and 13.2%, respectively, using ana-Si:H/nc-Si:H/nc-Si:H triple-junction structure.
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improved back reflector for high efficiency hydrogenated amorphous and Nanocrystalline Silicon based solar cells
MRS Proceedings, 2005Co-Authors: Baojie Yan, Chunsheng Jiang, Jessica M Owens, Jeffrey Yang, Subhendu GuhaAbstract:Ag/ZnO back reflectors (BR) on specular stainless steel substrates are optimized for hydrogenated amorphous Silicon germanium alloy (a-SiGe:H) and Nanocrystalline Silicon (nc-Si:H) solar cells. The BRs are deposited using a sputtering method. The texture of the Ag and ZnO layers is controlled by deposition parameters as well as chemical etching with diluted HCl. The surface morphology is investigated by atomic force microscopy. The scattered light intensity from a He-Ne laser, which illuminates the sample surface perpendicularly, is measured at different angles. Finally, a-SiGe:H and nc-Si:H solar cells are deposited on the BR substrates prepared under various conditions. For a-SiGe:H bottom cells, the improved BR with large micro-features leads to an enhanced open-circuit voltage. For the nc-Si:H solar cells, large micro-features on the improved BR eliminate interference fringes otherwise observed in the quantum efficiency measurement and result in high short circuit current density. The result is consistent with an enhanced scattered light intensity. Hence, the cell performance was improved. We also deposited a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on the optimized BR and achieved a high initial active-area efficiency of 14.6%.
S. Wagner - One of the best experts on this subject based on the ideXlab platform.
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Nanocrystalline Silicon thin film transistors on optically clear polymer foil substrates
2005Co-Authors: Alex Z. Kattamis, Ichun Cheng, Ke Long, J C Sturm, S. WagnerAbstract:We have fabricated TFTs of Nanocrystalline Silicon (nc-Si) at 150°C on clear polymer substrates (coefficients of thermal expansion, α~45 to 55ppm/K), on Kapton® 200E (α=17ppm/K), and on Corning 1737 glass (α=3ppm/K) for comparison. Because thermally stable polymers, such as Kapton® 200E polyimide, have glass transition temperatures as high as 325°C, they are candidates for direct substitution of display glass. The stresses developed in the substrate and device layers, due to α, are reduced by decreasing the thickness of the active layers, by cutting the layers into islands separated by exposed substrate, and by designing stresses, via plasma conditions, into the SiNx passivating layers. By using these three techniques we have made nc-Si TFTs on high Tg, and high α, clear polymer foils with electron mobilities of up to 18cm 2 /Vs. When integrated with bottom-emitting organic light emitting diodes, such devices will allow for a 10x reduction in pixel TFT areas, compared to TFTs of amorphous Silicon.
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Nanocrystalline Silicon thin film transistors with 50 nm thick deposited channel layer 10 cm2v 1s 1 electron mobility and 108 on off current ratio
Applied Physics A, 2002Co-Authors: Robert B Min, S. WagnerAbstract:Thin-film transistors were made using 50-nm-thick directly deposited Nanocrystalline Silicon channel layers. The transistors have a coplanar top gate structure. The Nanocrystalline Silicon was deposited from discharges in silane, hydrogen and Silicon tetrafluoride. The transistors combine a high electron field effect mobility of ∼10 cm2 V-1s-1 with a low ‘off’ current of ∼10-14 A per μm of channel length and an ‘on’/‘off’ current ratio of ∼108. This result shows that transistors made from directly deposited Silicon can combine high mobility with low ‘off’ currents.
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hole and electron field effect mobilities in Nanocrystalline Silicon deposited at 150 c
Applied Physics Letters, 2002Co-Authors: Ichun Cheng, S. WagnerAbstract:Field-effect structures were made from Nanocrystalline Silicon (nc-Si:H) deposited at a substrate temperature of 150 °C by plasma-enhanced chemical vapor deposition excited at 80 MHz. The nc-Si:H channel layer was grown on top of a separate nc-Si:H buffer and seed layer that serves to develop the crystalline structure. Staggering the contacts and the gate ensures that mobilities are measured precisely in the last-to-grow nc-Si:H layer. The hole mobility in saturation reaches 0.06–0.2 cm2 V−1 s−1 and the electron mobility ∼12 cm2 V−1 s−1. These results suggest that large-area circuits of complementary p- and n-channel devices can be made from nc-Si:H deposited on low-temperature substrates.
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Nanocrystalline Silicon tfts with 50 nm thick deposited channel layer 10 cm 2 vs electron mobility and 10 8 on off current ratio
MRS Proceedings, 2001Co-Authors: Robert B Min, S. WagnerAbstract:Thin film transistors were made using 50 nm thick directly deposited Nanocrystalline Silicon channel layers. The transistors have coplanar top gate structure. The Nanocrystalline Silicon was deposited from discharges in silane, hydrogen and Silicon tetrafluoride. The transistors combine a high electron field effect mobility of ∼ 10 cm 2 /Vs with a low “off” current of ∼ 10 −14 A per µm of channel length, and an “on”/“off” current ratio of ∼ 10 8 . This result shows that directly deposited Silicon can combine high mobility with low “off” currents.
Alves E - One of the best experts on this subject based on the ideXlab platform.
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Erbium-doped Nanocrystalline Silicon thin films produced by RF sputtering - Annealing effect on the Er emission
'Wiley', 2024Co-Authors: Cerqueira M.f., Monteiro T., Soares M.j, Kozanecki A., Alpuim P., Alves EAbstract:In the present work, erbium doped Nanocrystalline Silicon thin films were produced by reactive magnetron sputtering on glass substrates under different conditions (substrate temperature and Er content). The film structure was studied using Raman spectroscopy. The chemical composition was determined using the RBS technique. All the samples show sharp 4I13/2 → 4I15/2 intra-4f11 emission of Er 3+ related centres with its maximum positioned at the1.54 μm. However, the intensity of this transition (strongly dependent on the chemical composition of the matrix where the nanocrystals are embedded in and also on the structure of the matrix) changes after thermal annealing treatment. For the less crystalline samples our results show an increase of the Er3+ PL intensity and for the highly crystalline ones the Er emission vanishes even at low temperature. This behaviour was studied and explained in this work, on the basis of energy transfer between Si and Er ions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA
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Erbium-doped Nanocrystalline Silicon thin films produced by RF sputtering - Annealing effect on the Er emission
'Wiley', 2024Co-Authors: Cerqueira M.f., Kozanecki A., Alpuim P., Monteiro Teresa, Soares Manuel, Alves EAbstract:Partilhar documento na coleção da comunidade Laboratório Associado I3NIn the present work, erbium doped Nanocrystalline Silicon thin films were produced by reactive magnetron sputtering on glass substrates under different conditions (substrate temperature and Er content). The film structure was studied using Raman spectroscopy. The chemical composition was determined using the RBS technique. All the samples show sharp 4I13/2 → 4I15/2 intra-4f11 emission of Er 3+ related centres with its maximum positioned at the1.54 μm. However, the intensity of this transition (strongly dependent on the chemical composition of the matrix where the nanocrystals are embedded in and also on the structure of the matrix) changes after thermal annealing treatment. For the less crystalline samples our results show an increase of the Er3+ PL intensity and for the highly crystalline ones the Er emission vanishes even at low temperature. This behaviour was studied and explained in this work, on the basis of energy transfer between Si and Er ions
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Influence of crystals distribution on the photoluminescence properties of Nanocrystalline Silicon thin films
'Elsevier BV', 2024Co-Authors: Cerqueira M.f., Monteiro T., Soares M.j, Alves E, Stepikhova M., Losurdo M., Giangregorio M.m., Boemare C.Abstract:Nanocrystalline Silicon thin films doped with erbium were produced by reactive magnetron RF sputtering. Their structural and chemical properties were studied by X-ray diffractometry at grazing incidence, micro-Raman, spectroscopic ellipsometry and Rutherford Backscattering Spectroscopy, respectively. Films with different crystalline fraction and crystallite size were deposited. Since the luminescence efficiency of Er-doped nc-Si films is strongly influenced by the microstructure and impurity content (i.e. H, O, Er), the photoluminescence characteristics are discussed in terms of the microstructure. The novelty of these films, if compared to usually investigated structures with the nanocrystals embedded in SiO2, is their relative high conductivity, which makes them attractive for device application
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Study of the oxygen role in the photoluminescence of erbium doped Nanocrystalline Silicon embedded in a Silicon amorphous matrix
'Elsevier BV', 2024Co-Authors: Cerqueira M. F., Monteiro T., Stepikhova M., Losurdo M., Soares M. J., Peres M., Alves EAbstract:We have produced and studied erbium doped Nanocrystalline Silicon thin films with different oxygen and hydrogen content in order to evaluate the influence of the matrix on the Er3+ emission and on the 0.89 eV and 1.17 eV bands. Films were grown by reactive magnetron sputtering on glass substrates under several different conditions (RF power, Er content and gas mixture composition) in order to obtain different microstructures. The structural parameters and the chemical composition of the samples were obtained by X-ray in the grazing incidence geometry, Raman spectroscopy and Rutherford back scattering analysis. Using X-ray technique combined with Raman spectroscopy information on the crystalline fraction and the average crystallite size of Si nanocrystals was obtained. Dependence of the 0.89 eV and 1.17 eV peaks in Si heterogeneous matrixes on the films crystallinity and O/H ratio has been analyzed.FCT - POCTI/CTM/39395/2001INTAS #03-51-648
