We observe the simultaneous creation of paramagnetic Si and N dangling bonds when N-rich silicon ... more We observe the simultaneous creation of paramagnetic Si and N dangling bonds when N-rich silicon nitride thin films are optically illuminated at low temperatures (110 K). Generally, only the Si dangling bond is observed if the illumination is performed at room temperature. In contrast, the N dangling bond is metastable, and has previously only been observed after a high temperature post-deposition anneal and followed by illumination. We propose that the low temperature illumination causes two processes: (1) Charge conversion of N3≡Si+ and N3≡Si− sites to give two N3≡Si⋅dangling bonds, and (2) charge transfer between Si2=N− and N3≡Si+ sites to form Si2=N⋅ and N3≡Si⋅dangling bonds.
Optics and Photonics for Counterterrorism, Crime Fighting, and Defence XI; and Optical Materials and Biomaterials in Security and Defence Systems Technology XII, 2015
ABSTRACTThe creation mechanisms of Si and N dangling bond defect centers in amorphous hydrogenate... more ABSTRACTThe creation mechanisms of Si and N dangling bond defect centers in amorphous hydrogenated silicon nitride thin films by ultra-violet (UV) illumination are investigated. The creation efficiency and density of Si centers in the N-rich films are independent of illumination temperature, strongly suggesting that the creation mechanism of the spins is electronic in nature, i.e., a charge transfer mechanism. However, our results suggest that the creation of the Si dangling bond in the Si-rich films are different. Last, we find that the creation of the N dangling-bond in N-rich films can be fit to a stretched exponential time dependence, which is characteristic of dispersive charge transport.
Fundacao para a Ciencia e Tecnologia (Portugal) for FEDER (PEst-C/QUI/UI0686/2013) , and European... more Fundacao para a Ciencia e Tecnologia (Portugal) for FEDER (PEst-C/QUI/UI0686/2013) , and European Community for FP7-PEOPLE-2009-IRSES Biomolec – 247544 for the financial support given to this research.
2012 19th International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2012
We reported on optoelectronic properties of the Cu(InGa)Se2 (CIGS) solar cell fabricated by sputt... more We reported on optoelectronic properties of the Cu(InGa)Se2 (CIGS) solar cell fabricated by sputtering method on stainless steel substrate having external efficiency of ~13.0%. Experimental data indicates that the quantum efficiency (QE) has a high response for long wavelength light. Current density (J) - voltage (V) measurements under illumination resulted in short circuit current density of 32.08 mA/cm2 and open circuit voltage of 0.55 V. We have also performed modeling of this device establishing that both experimental and calculated data are consistent with each other.
The channel length (L) and width (W) scaling behavior of amorphous In-Ga-Zn-O thin-film transisto... more The channel length (L) and width (W) scaling behavior of amorphous In-Ga-Zn-O thin-film transistors (TFTs) have been investigated. The fabricated TFTs have a mobility of ~12 cm2/V-s, sub-threshold slope (S) of ~110 mV/decade, threshold voltage around 0.3 V and off-current below 10-13 A. Even though the TFTs with smaller channel length (L ≤ 5 μm) show proper switching characteristics, threshold voltage lowering and sub-threshold slope degradation are observed, while off-current and mobility are not changed. The mobility degradation with L, which was observed in amorphous silicon TFTs, is not seen for short channel a-IGZO TFTs. Lastly, the necessity of the TFT scaling for a pixel electrode in AM-LCD applications is discussed.
ABSTRACT The photoelectrochemistry of Crystal Violet, Methyl Violet and Malachite Green in the pr... more ABSTRACT The photoelectrochemistry of Crystal Violet, Methyl Violet and Malachite Green in the presence of hydroquinone is examined at the SnO2 bubbling gas electrode. For the first two dyes, the Stern-Volmer constants of the process responsible for the supersensitization, determined by the previously described (1) electrochemical method, could correspond to the quenching either of the oxidized dye or of the excited triplet state. An interesting new feature emerges from the study of the Malachite Green-hydroquinone system: two species seem to be involved in the supersensitization process having rather different lifetimes, and thus quenched in different hydroquinone concentration ranges.
We observe the simultaneous creation of paramagnetic Si and N dangling bonds when N-rich silicon ... more We observe the simultaneous creation of paramagnetic Si and N dangling bonds when N-rich silicon nitride thin films are optically illuminated at low temperatures (110 K). Generally, only the Si dangling bond is observed if the illumination is performed at room temperature. In contrast, the N dangling bond is metastable, and has previously only been observed after a high temperature post-deposition anneal and followed by illumination. We propose that the low temperature illumination causes two processes: (1) Charge conversion of N3≡Si+ and N3≡Si− sites to give two N3≡Si⋅dangling bonds, and (2) charge transfer between Si2=N− and N3≡Si+ sites to form Si2=N⋅ and N3≡Si⋅dangling bonds.
Optics and Photonics for Counterterrorism, Crime Fighting, and Defence XI; and Optical Materials and Biomaterials in Security and Defence Systems Technology XII, 2015
ABSTRACTThe creation mechanisms of Si and N dangling bond defect centers in amorphous hydrogenate... more ABSTRACTThe creation mechanisms of Si and N dangling bond defect centers in amorphous hydrogenated silicon nitride thin films by ultra-violet (UV) illumination are investigated. The creation efficiency and density of Si centers in the N-rich films are independent of illumination temperature, strongly suggesting that the creation mechanism of the spins is electronic in nature, i.e., a charge transfer mechanism. However, our results suggest that the creation of the Si dangling bond in the Si-rich films are different. Last, we find that the creation of the N dangling-bond in N-rich films can be fit to a stretched exponential time dependence, which is characteristic of dispersive charge transport.
Fundacao para a Ciencia e Tecnologia (Portugal) for FEDER (PEst-C/QUI/UI0686/2013) , and European... more Fundacao para a Ciencia e Tecnologia (Portugal) for FEDER (PEst-C/QUI/UI0686/2013) , and European Community for FP7-PEOPLE-2009-IRSES Biomolec – 247544 for the financial support given to this research.
2012 19th International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2012
We reported on optoelectronic properties of the Cu(InGa)Se2 (CIGS) solar cell fabricated by sputt... more We reported on optoelectronic properties of the Cu(InGa)Se2 (CIGS) solar cell fabricated by sputtering method on stainless steel substrate having external efficiency of ~13.0%. Experimental data indicates that the quantum efficiency (QE) has a high response for long wavelength light. Current density (J) - voltage (V) measurements under illumination resulted in short circuit current density of 32.08 mA/cm2 and open circuit voltage of 0.55 V. We have also performed modeling of this device establishing that both experimental and calculated data are consistent with each other.
The channel length (L) and width (W) scaling behavior of amorphous In-Ga-Zn-O thin-film transisto... more The channel length (L) and width (W) scaling behavior of amorphous In-Ga-Zn-O thin-film transistors (TFTs) have been investigated. The fabricated TFTs have a mobility of ~12 cm2/V-s, sub-threshold slope (S) of ~110 mV/decade, threshold voltage around 0.3 V and off-current below 10-13 A. Even though the TFTs with smaller channel length (L ≤ 5 μm) show proper switching characteristics, threshold voltage lowering and sub-threshold slope degradation are observed, while off-current and mobility are not changed. The mobility degradation with L, which was observed in amorphous silicon TFTs, is not seen for short channel a-IGZO TFTs. Lastly, the necessity of the TFT scaling for a pixel electrode in AM-LCD applications is discussed.
ABSTRACT The photoelectrochemistry of Crystal Violet, Methyl Violet and Malachite Green in the pr... more ABSTRACT The photoelectrochemistry of Crystal Violet, Methyl Violet and Malachite Green in the presence of hydroquinone is examined at the SnO2 bubbling gas electrode. For the first two dyes, the Stern-Volmer constants of the process responsible for the supersensitization, determined by the previously described (1) electrochemical method, could correspond to the quenching either of the oxidized dye or of the excited triplet state. An interesting new feature emerges from the study of the Malachite Green-hydroquinone system: two species seem to be involved in the supersensitization process having rather different lifetimes, and thus quenched in different hydroquinone concentration ranges.
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