Current Search: electron injection (x)
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- Title
- FABRICATION AND TRANSPORT STUDIES OF N-TYPE ORGANIC FIELD EFFECT TRANSISTORS USING ALIGNED ARRAY CARBON NANOTUBES ELECTRODES.
- Creator
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Jimenez, Edwards, Khondaker, Saiful, University of Central Florida
- Abstract / Description
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We present fabrication of n-type organic field effect transistors (OFETs) using densely aligned array carbon nanotube (CNT) electrodes. The CNTs were aligned with a high linear density via dielectrophoresis (DEP) from an aqueous solution. In order to fabricate the CNT electrodes, aligned CNTs were cut by using electron beam lithography (EBL) and precise oxygen plasma etching. The n-type OFETs were fabricated in a bottom-contact configuration by depositing a thin film of C60 molecules between...
Show moreWe present fabrication of n-type organic field effect transistors (OFETs) using densely aligned array carbon nanotube (CNT) electrodes. The CNTs were aligned with a high linear density via dielectrophoresis (DEP) from an aqueous solution. In order to fabricate the CNT electrodes, aligned CNTs were cut by using electron beam lithography (EBL) and precise oxygen plasma etching. The n-type OFETs were fabricated in a bottom-contact configuration by depositing a thin film of C60 molecules between the CNT source and drain electrodes, and compared against a controlled C60 OFET with gold electrodes. The electron transport measurements of the OFETs using CNT electrodes show better transistor characteristics compared to OFETs using gold electrodes due to improved charge injection from densely aligned and open-ended nanotube tips.
Show less - Date Issued
- 2012
- Identifier
- CFH0004217, ucf:44941
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004217
- Title
- Electronic and Optoelectronic Transport Properties of Carbon Nanotube/Organic Semiconductor Devices.
- Creator
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Sarker, Biddut, Khondaker, Saiful, Schulte, Alfons, Stolbov, Sergey, Gesquiere, Andre, University of Central Florida
- Abstract / Description
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Organic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising...
Show moreOrganic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising electrode material which can address this challenge.In this dissertation, we demonstrate fabrication of high-performance OFETs using aligned array CNT electrodes and investigate the detailed electronic transport properties of the fabricated devices. The OFETs with CNT electrodes show a remarkable enhancement in the device performance such as high mobility, high current on-off ratio, higher cutoff frequency, absence of short channel effect and better charge carrier injection than those OFETs with metal electrodes. From the low temperature transport measurements, we show that the charge injection barrier at CNT/OSC interface is smaller than that of the metal/OSC interface. A transition from direct tunneling to Fowler-Nordheim tunneling observed in CNT/OSC system shows further evidence of low injection barrier. A lower activation energy measured for the OFETs with CNT electrodes gives evidence of lower interfacial trap states. Finally, OFETs are demonstrated by directly growing crystalline organic nanowires on aligned array CNT electrodes.In addition to investigating the interfacial barrier at CNT/OSC interface, we also studied photoconduction mechanism of the CNT and CNT/OSC nanocomposite thin film devices. We found that the photoconduction is due to the exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode/CNT interface and diffusion of the charge carrier through percolating CNT networks. In addition, it is found that photoresponse of the CNT/organic semiconductor can be tuned by changing the weight percentage of CNT into the organic semiconductors.
Show less - Date Issued
- 2012
- Identifier
- CFE0004596, ucf:49217
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004596
- Title
- Charge and Spin Transport in Low-Dimensional Materials.
- Creator
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Ahmadi, Amin, Mucciolo, Eduardo, Del Barco, Enrique, Ishigami, Masa, Guo, Jing, University of Central Florida
- Abstract / Description
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My research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon...
Show moreMy research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon nanotube. The second part of my study was concerned to the dynamicalspin injection and spin currents in low-dimensional materials. We have developed an atomisticmodel to express the injected spin current in terms of the systems Greens function. The newformulation provides a framework to study the spin injection and relaxation of a system with anarbitrary structure.
Show less - Date Issued
- 2017
- Identifier
- CFE0006550, ucf:51343
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006550
- Title
- ELECTRON INJECTION-INDUCED EFFECTS IN III-NITRIDES: PHYSICS AND APPLICATIONS.
- Creator
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Burdett, William Charles, Chernyak, Leonid, University of Central Florida
- Abstract / Description
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This research investigated the effect of electron injection in III-Nitrides. The combination of electron beam induced current and cathodoluminescence measurements was used to understand the impact of electron injection on the minority carrier transport and optical properties. In addition, the application of the electron injection effect in optoelectronic devices was investigated.The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in Mg...
Show moreThis research investigated the effect of electron injection in III-Nitrides. The combination of electron beam induced current and cathodoluminescence measurements was used to understand the impact of electron injection on the minority carrier transport and optical properties. In addition, the application of the electron injection effect in optoelectronic devices was investigated.The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in Mg-doped p-GaN, p-AlxGa1-xN, and p-AlxGa1-x N/GaN superlattices. It was found that the minority carrier diffusion length experienced a multi-fold linear increase and that the rate of change of the diffusion length decreased exponentially with increasing temperature. The effect was attributed to a temperature-activated release of the electrons, which were trapped by the Mg levels.The activation energies for the electron injection effect in the Mg-doped (Al)GaN samples were found to range from 178 to 267 meV, which is close to the thermal ionization energy of the Mg acceptor. The activation energy observed for Al0.15Ga0.85N and Al0.2Ga0.8N was consistent with the deepening of the Mg acceptor level due to the incorporation of Al into the GaN lattice. The activation energy in the homogeneously doped Al0.2Ga0.8N/GaN superlattice indicates that the main contribution to the electron injection effect comes from the capture of injected electrons by the wells (GaN). The electron injection effect was successfully applied to GaN doped with an impurity (Mn) other than Mg. Electron injection into Mn-doped GaN resulted in a multi-fold increase of the minority carrier diffusion length and a pronounced decrease in the band-to-band cathodoluminescence intensity. The activation energy due to the electron injection effect was estimated from temperature-dependent cathodoluminescence measurements to be 360 meV. The decrease in the band-to-band cathodoluminescence is consistent with an increase in the diffusion length and these results are attributed to an increase in the minority carrier lifetime due to the trapping of injected electrons by the Mn levels.A forward bias was applied to inject electrons into commercially built p-i-n and Schottky barrier photodetectors. Up to an order of magnitude increase in the peak (360 nm) responsivity was observed. The enhanced photoresponse lasted for over four weeks and was attributed to an electron injection-induced increase of the minority carrier diffsuion length and the lifetime.
Show less - Date Issued
- 2004
- Identifier
- CFE0000080, ucf:46109
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000080
- Title
- Injection Locking of Semiconductor Mode-Locked Lasers for Long-Term Stability of Widely Tunable Frequency Combs.
- Creator
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Williams, Charles, Delfyett, Peter, Hagan, David, Likamwa, Patrick, Vanstryland, Eric, DeSalvo, Richard, University of Central Florida
- Abstract / Description
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Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall...
Show moreHarmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall stabilization or by polarization spectroscopy. Error signals of both techniques are simulated and compared to experimentally obtained signals. Frequency combs spaced by 2.5 GHz and ~10 GHz are generated, with demonstrated optical sidemode suppression of unwanted modes of 36 dB, as well as RF supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of actively harmonically mode-locked lasers, the injection locking technique for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEOs), is also demonstrated and characterized extensively.
Show less - Date Issued
- 2013
- Identifier
- CFE0004774, ucf:49805
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004774