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- Title
- INVESTIGATION OF REACTIVELY SPUTTERED SILICON CARBON BORON NITRIDE (SICBN) THIN FILMS FOR HIGH TEMPERATURE APPLICATIONS.
- Creator
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Vijayakumar, Arun, Sundaram, Kalpathy, University of Central Florida
- Abstract / Description
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The increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of...
Show moreThe increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of the component during operation. They provide the basic advantage of proximity to the surface and hence accurate measurement of the surface temperature. The low mass size ratio provides the additional advantage of least interference to system operation. The four elements consisting of Si, C, B, and N can be used to form binary, ternary and quaternary compounds like carbides, nitrides, which are chemically and thermally stable with extreme hardness, thermal conductivity and can be doped n- and p-type. Hence these compounds can be potential candidates for high temperature applications. This research is focused on studying sputtering as a candidate to obtain thin SiCBN films. The deposition and characterization of amorphous thin films of silicon boron carbon nitride (SiCBN) is reported. The SiCBN thin films were deposited in a radio frequency (rf) magnetron sputtering system using reactive co-sputtering of silicon carbide (SiC) and boron nitride (BN) targets. Films of different compositions were deposited by varying the ratios of argon and nitrogen gas in the sputtering ambient. Investigation of the oxidation kinetics of these materials was performed to study high temperature compatibility of the material. Surface characterization of the deposited films was performed using X-ray photoelectron spectroscopy and optical profilometry. Studies reveal that the chemical state of the films is highly sensitive to nitrogen flow ratios during sputtering. Surface analysis shows that smooth and uniform SiCBN films can be produced using this technique. Carbon and nitrogen content in the films seem to be sensitive to annealing temperatures. However depth profile studies reveal certain stoichiometric compositions to be stable after high temperature anneal up to 900ºC. Electrical and optical characteristics are also investigated with interesting results. Finally a metal semiconductor metal structure based optoelectronic device is demonstrated with excellent performance improvement over standard silicon based devices under higher temperature conditions.
Show less - Date Issued
- 2007
- Identifier
- CFE0001914, ucf:47490
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001914
- Title
- Nanoplasmonics In Two-dimensional Dirac and Three-dimensional Metallic Nanostructure Systems.
- Creator
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Safaei, Alireza, Chanda, Debashis, Leuenberger, Michael, Mucciolo, Eduardo, Tetard, Laurene, Zhai, Lei, University of Central Florida
- Abstract / Description
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Surface plasmons are collective oscillation of electrons which are coupled to the incident electric field. Excitation of surface plasmon is a route to engineer the behavior of light in nanometer length scale and amplifying the light-matter interaction. This interaction is an outcome of near-field enhancement close to the metal surface which leads to plasmon damping through radiative decay to outgoing photons and nonradiative decay inside and on the surface of the material to create an...
Show moreSurface plasmons are collective oscillation of electrons which are coupled to the incident electric field. Excitation of surface plasmon is a route to engineer the behavior of light in nanometer length scale and amplifying the light-matter interaction. This interaction is an outcome of near-field enhancement close to the metal surface which leads to plasmon damping through radiative decay to outgoing photons and nonradiative decay inside and on the surface of the material to create an electron-hole pair via interband or intraband Landau damping. Plasmonics in Dirac systems such as graphene show novel features due to massless electrons and holes around the Dirac cones. Linear band structure of Dirac materials in the low-momentum limit gives rise to the unprecedented optical and electrical properties. Electronical tunability of the plasmon resonance frequency through applying a gate voltage, highly confined electric field, and low plasmon damping are the other special propoerties of the Dirac plasmons. In this work, I will summarize the theoretical and experimental aspects of the electrostatical tunable systems made from monolayer graphene working in mid-infrared regime. I will demonstrate how a cavity-coupled nanopatterned graphene excites Dirac plasmons and enhances the light-matter interaction. The resonance frequency of the Dirac plasmons is tunable by applying a gate voltage. I will show how different gate-dielectrics, and the external conditions like the polarization and angle of incident light affect on the optical response of the nanostructure systems. I will then show the application of these nanodevices in infrared detection at room temperature by using plasmon-assisted hot carriers generation. An asymmetric nanopatterned graphene shows a high responsivity at room temperature which is unprecedented. At the end, I will demonstrate the properties of surface plasmons on 3D noble metals and its applications in light-funneling, photodetection, and light-focusing.
Show less - Date Issued
- 2019
- Identifier
- CFE0007904, ucf:52746
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007904
- 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
- Growth and Characterization of ZnO Based Semiconductor Materials and Devices.
- Creator
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Wei, Ming, Schoenfeld, Winston, Likamwa, Patrick, Moharam, M., Wu, Shintson, Osinsky, Andrei, University of Central Florida
- Abstract / Description
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Wide band gap semiconductors such as MgxZn1-xO represent an excellent choice for making optical photodetectors and emitters operating in the UV spectral region. High crystal and optical quality MgxZn1-xO thin films were grown epitaxially on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy. ZnO thin films with high crystalline quality, low defect and dislocation densities, and sub-nanometer surface roughness were achieved by applying a low temperature nucleation layer. The...
Show moreWide band gap semiconductors such as MgxZn1-xO represent an excellent choice for making optical photodetectors and emitters operating in the UV spectral region. High crystal and optical quality MgxZn1-xO thin films were grown epitaxially on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy. ZnO thin films with high crystalline quality, low defect and dislocation densities, and sub-nanometer surface roughness were achieved by applying a low temperature nucleation layer. The critical growth conditions were discussed to obtain a high quality film: the sequence of Zn and O sources for initial growth of nucleation layer, growth temperatures for both ZnO nucleation and growth layers, and Zn/O ratio. By tuning Mg/Zn flux ratio, wurtzite MgxZn1-xO thin films with Mg composition as high as x=0.46 were obtained without phase segregation. The steep optical absorption edges were shown with a cut-off wavelength as short as 278nm, indicating of suitability of such material for solar blind photo detectors. Consequently, Metal-Semiconductor-Metal photoconductive and Schottky barrier devices with interdigital electrode geometry and active surface area of 1 mm2 were fabricated and characterized. Photoconductor based on showed ~100 A/W peak responsivity at wavelength of ~260nm. ZnO homoepitaxial growth was also demonstrated which has the potential to achieve very low dislocation densities and high efficiency LEDs. Two types of Zn-polar ZnO substrates were chosen in this study: one with 0.5(&)deg; miscut angle toward the [1-100] direction and the other without any miscut angle. We have demonstrated high quality films on both substrates with a low growth temperature (610(&)deg;C) compared to most of other reported work on homoepitaxial growth. An atomically flat surface with one or two monolayer step height along the [0001] direction was achieved. By detail discussions about several impact factors for the epitaxial films, ZnO films with high crystallinity verified by XRD in different crystal orientations, high PL lifetime (~0.35 ns), and not obvious threading dislocations were achieved.Due to the difficulty of conventional p-type doping with p dopant, we have explored the possibility of p-type doping with the assistance of other novel method, i.e. polarization induced effect. The idea is the sheet layer of two dimensional hole gases (2DHG) caused by the wurtzite structure's intrinsic polarization effect can be expanded to three dimension hole distribution by growing a MgZnO layer with a Mg concentration gradient. By simulation of LED structure with gradient MgZnO structure, the polarization effect was found not intense as that for III-nitrides because the difference of spontaneous polarization between ZnO and MgO is smaller than that of GaN and AlN, and the piezoelectric polarization effect may even cancel the spontaneous polarization induced effect. We have grown the linear gradient MgZnO structure with Mg composition grading from 0% to 43%, confirmed by SIMS. Hall measurement did not show any p-type conductivity, which further indicates MgZnO's weak polarization doping effect. However, the gradient MgZnO layer could act as an electron blocking layer without blocking holes injected from p layer, which is useful for high efficiency light emitters.
Show less - Date Issued
- 2013
- Identifier
- CFE0005275, ucf:50544
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005275