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Photoluminescence

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Articles 31 - 60 of 92

Full-Text Articles in Physics

Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian Jan 2016

Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian

Theses and Dissertations

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that …

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Time-Resolved Photoluminescence Studies Of Point Defects In Gan, Joy Dorene Mcnamara Jan 2016

Time-Resolved Photoluminescence Studies Of Point Defects In Gan, Joy Dorene Mcnamara

Theses and Dissertations

Time-resolved photoluminescence (TRPL) measurements paired with steady-state photoluminescence (SSPL) measurements can help to determine the PL lifetime, shape and position of unresolved bands, capture coefficients, and concentrations of free electrons and defects.PL bands that are obscured in the SSPL spectra can be accurately revealed by TRPL measurements. TRPL measurements are able to show if the PL band originates from an internal transition between different states of the same defect. The main defect-related PL bands in high-purity GaN grown by hydride vapor phase epitaxy (HVPE) which have been investigated are the ultraviolet, blue, green, yellow and red luminescence bands (UVL, BL, …

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Bimetallic-Waveguide Coupled Sensors For Tunable Plasmonic Devices, Kunal K. Tiwari Dec 2015

Bimetallic-Waveguide Coupled Sensors For Tunable Plasmonic Devices, Kunal K. Tiwari

Physics Dissertations - Archive

Surface plasmon resonance (SPR) has been a widely used optical technique for the real time and label free sensing applications in biomedicine, homeland security, food safety, environmental monitoring, etc. Surface plasmons (SPs) being extremely sensitive to the surrounding media, their characteristics can be modulated by tuning their dielectric environment. The unique property of the nematic liquid crystalline materials that their dielectric constant can be tuned by externally applied electric fields formed the basis for development of tunable plasmonic sensor for monitoring changes at metal/dielectric interfaces. Even though sensors with high sensitivity are available, it remains highly desirable to enhance sensor …

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The Fabrication And Characterization Of High-Quality Inxga1-Xn Nanorods (0.28, Samir Mustafa Hamad Mar 2015

The Fabrication And Characterization Of High-Quality Inxga1-Xn Nanorods (0.28, Samir Mustafa Hamad

Theses and Dissertations

Wurtzite InxGa1-x N (0001) nanorods have been grown on Si (111) substrate by plasma-assisted molecular beam epitaxy (PA-MBE) methods without any heterocatalyst. The InxGa1-x N ( ~0.3 < x< ~ 0.4) is a unique material as high-brightness light emitting diodes (LEDs), laser diodes (LDs), which may emit/detect the green/blue light. However, the growth of the high quality of InxGa1-x N with a tunable bandgap, having a 30~40% of In content, is not formidable due to thermodynamic & kinetic limitations in the alloy formations. For instance, the miscibility gap induced phase separation and In segregation on the growth surface are the cases. In this dissertation, we will report the growth of high quality InxGa1-x N nanorods in relation to the growth parameters, substrate temperature, In/Ga ratio, group-III (In+Ga) flux, and Group V flux, with understanding the physics behind. Using in-situ reflection high-energy electron diffraction, the surface crystal structure was monitored. The morphological and optical properties of InxGa1-x N nanorods were characterized by scanning electron microscopy and dual-light room-temperature photoluminescence methods. In addition, the nitrogen species from plasma source, which contribute to the growth, was studied by measuring optical emission spectroscopy.

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Hybrid Type-I Inas/Gaas And Type-Ii Gasb/Gaas Quantum Dot Structure With Enhanced Photoluminescence, Hai-Ming Ji, Baolai Liang, Paul J. Simmonds, Bor-Chau Juang, Tao Yang, Robert J. Young, Diana L. Huffaker Mar 2015

Hybrid Type-I Inas/Gaas And Type-Ii Gasb/Gaas Quantum Dot Structure With Enhanced Photoluminescence, Hai-Ming Ji, Baolai Liang, Paul J. Simmonds, Bor-Chau Juang, Tao Yang, Robert J. Young, Diana L. Huffaker

Physics Faculty Publications and Presentations

We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL.These hybrid QD structures show potential for high efficiency QD solar cell applications.

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Identification Of Point Defects In Hvpe-Grown Gan By Steady-State And Time-Resolved Photoluminescence, Michael A. Reshchikov, Denis O. Demchenko, A Usikov, H Helava, Yu. Makarov Jan 2015

Identification Of Point Defects In Hvpe-Grown Gan By Steady-State And Time-Resolved Photoluminescence, Michael A. Reshchikov, Denis O. Demchenko, A Usikov, H Helava, Yu. Makarov

Forensic Science Publications

We have investigated point defects in GaN grown by HVPE by using steady-state and time-resolved photoluminescence (PL). Among the most common PL bands in this material are the red luminescence band with a maximum at 1.8 eV and a zero-phonon line (ZPL) at 2.36 eV (attributed to an unknown acceptor having an energy level 1.130 eV above the valence band), the blue luminescence band with a maximum at 2.9 eV (attributed to ZnGa), and the ultraviolet luminescence band with the main peak at 3.27 eV (related to an unknown shallow acceptor). In GaN with the highest quality, the dominant defect-related …

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Defect-Related Luminescence In Undoped Gan Grown By Hvpe, Michael A. Reshchikov, A Usikov, H Helava, Yu. Makarov Jan 2015

Defect-Related Luminescence In Undoped Gan Grown By Hvpe, Michael A. Reshchikov, A Usikov, H Helava, Yu. Makarov

Forensic Science Publications

Hydride vapor phase epitaxy (HVPE) is used for the growth of low-defect GaN. We have grown undoped films on sapphire and investigated them using steady-state and time-resolved photoluminescence (PL). One of the dominant PL bands in high-quality GaN grown by HVPE is the green luminescence (GL) band with a maximum at 2.4 eV. This PL band can be easily recognized in time-resolved PL measurements due to its exponential decay even at low temperatures (<50 K), with a characteristic lifetime of 1–2 μs. As the temperature increases from 70 K to 280 K, the PL lifetime for the GL band increases by an order of magnitude. This …

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Investigation Of Optical And Electronic Properties Of Au Decorated Mos2, Udai Bhanu Jan 2015

Investigation Of Optical And Electronic Properties Of Au Decorated Mos2, Udai Bhanu

Electronic Theses and Dissertations

Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate optical and electronic properties due to charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, catalysis, and biosensing. Here in this dissertation, we study the charge transfer interaction between Au nanoparticals and MoS2 flakes and its …

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Strain-Driven Growth Of Gaas(111) Quantum Dots With Low Fine Structure Splitting, Paul J. Simmonds Dec 2014

Strain-Driven Growth Of Gaas(111) Quantum Dots With Low Fine Structure Splitting, Paul J. Simmonds

Physics Faculty Publications and Presentations

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting(FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with …

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Control Of Light-Matter Interaction Via Dispersion Engineering, Harish Natarajan Swaha Krishnamoorthy Oct 2014

Control Of Light-Matter Interaction Via Dispersion Engineering, Harish Natarajan Swaha Krishnamoorthy

Dissertations, Theses, and Capstone Projects

This thesis describes the design, fabrication and characterization of certain nanostructures to engineer light-matter interaction. These materials have peculiar dispersion properties owing to their structural design, which is exploited to control spontaneous emission properties of emitters such as quantum dots and dye molecules. We will discuss two classes of materials based on the size of their unit cell compared to the wavelength of the electromagnetic radiation they interact with. The first class are hyperbolic metamaterials (HMM) composed of alternate layers of a metal and a dielectric of thicknesses much smaller than the wave- length. Using a HMM composed of silver …

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Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov Jan 2014

Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov

Physics Publications

Mechanisms of thermal quenching of photoluminescence (PL) related to defects insemiconductors are analyzed. We conclude that the Schön-Klasens (multi-center) mechanism of the thermal quenching of PL is much more common for defects in III–V and II–VI semiconductorsas compared to the Seitz-Mott (one-center) mechanism. The temperature dependencies of PLare simulated with a phenomenological model. In its simplest version, three types of defects are included: a shallow donor, an acceptor responsible for the PL, and a nonradiative center that has the highest recombination efficiency. The case of abrupt and tunable thermal quenching ofPL is considered in more detail. This phenomenon is predicted …

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Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov Jan 2014

Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov

Physics Publications

Point defects in GaN were studied with time-resolved photoluminescence (PL). The effects of temperature and excitation intensity on defect-related PL have been investigated theoretically and experimentally. A phenomenological model, based on rate equations, explains the dependence of the PL intensity on excitation intensity, as well as the PL lifetime and its temperature dependence. We demonstrate that time-resolved PL measurements can be used to find the concentrations of free electrons and acceptors contributing to PL in n-type semiconductors.

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Optical And Magnetic Properties Of Nanostructures, Neha Nayyar Jan 2014

Optical And Magnetic Properties Of Nanostructures, Neha Nayyar

Electronic Theses and Dissertations

In this thesis, Density Functional Theory and Time-Dependent Density-Functional Theory approaches are applied to study the optical and magnetic properties of several types of nanostructures. In studies of the optical properties we mainly focused on the plasmonic and excitonic effects in pure and transition metal-doped noble metal nanochains and their conglomerates. In the case of pure noble metal chains, it was found that the (collective) plasmon mode is pronounceable when the number of atoms in the chain is larger than 5. The plasmon energy decreases with further with increasing number of atoms (N) and is almost N-independent when N is …

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The Effect Of Temperature On The Electrical And Optical Properties Of P-Type Gan, Joy Mcnamara May 2013

The Effect Of Temperature On The Electrical And Optical Properties Of P-Type Gan, Joy Mcnamara

Theses and Dissertations

The development of gallium nitride (GaN) light emitting devices has reached extraordinary echelons. As such, the characterization and analysis of the behavior of GaN materials is essential to the advancement of GaN technology. In this thesis, the effect of temperature on the optical and electrical properties of p-type GaN is investigated. The GaN samples used in this work were grown by various methods and studied by Kelvin probe and photoluminescence (PL) techniques. Specifically, the surface photovoltage (SPV) behavior and PL data were analyzed at different temperatures and illumination intensities. Using the SPV results, we show that p-type GaN exhibits n-type …

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Electrodeposition Of Zno Nanowires: Growth, Doping, And Physical Properties, Matthew Allan Thomas Mar 2013

Electrodeposition Of Zno Nanowires: Growth, Doping, And Physical Properties, Matthew Allan Thomas

Theses and Dissertations

As a transparent, wide bandgap semiconductor, ZnO offers an expansive range of potential uses in various technological arenas such as electronics, optoelectronics, photonics, sensors, and energy conversion. However, a current obstacle to the realization of ZnO based electronics and optoelectronics is the lack of a reliable and reproducible method for fabricating high quality p-type ZnO. In addition, there remains a difficulty in tuning the various properties of ZnO materials, especially nanostructures, via low cost and low temperature deposition techniques. In this work, some of these deficiencies have been addressed. Undoped and Ag-doped ZnO nanowires, as well as highly uniform and …

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Defect Studies In Strain-Relaxed Si_{1-X}Ge_X Alloys, Şeref Kalem Jan 2013

Defect Studies In Strain-Relaxed Si_{1-X}Ge_X Alloys, Şeref Kalem

Turkish Journal of Physics

Raman light scattering, low-temperature photoluminescence, light-scattering tomography, and hydrogenation were used to investigate optical properties of defects in strain-relaxed Si_{1-x}Ge_x (0.05 \le x \le 0.50) alloys. The photoluminescence emission was characterized by typical zero-phonon, phonon-assisted, and dislocations-related emissions, which are dependent on Ge composition x. However, luminescence spectra exhibited above band-gap features, which are likely associated with the presence of Si-rich regions in the alloys. The results are correlated with light-scattering tomography, revealing the presence of dislocations and Si precipitates. The excess peak at 519 cm^{-1} in Ge-rich samples is supportive of this observation. At low Ge content, a dislocation-related …

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Thermal Quenching Of Photoluminescence From Gan, Anita Olsen Apr 2012

Thermal Quenching Of Photoluminescence From Gan, Anita Olsen

Theses and Dissertations

GaN is a III-V semiconductor that is a promising material used in production of light emitting devices and high power/high frequency electronics. The electronic and optical properties of GaN are subdued by defects that occur during the growth processes of this material. The emitted photoluminescence (PL) from optically excited GaN gives insight into the origins and effects of point defects within the crystal lattice structure of GaN. In this study, PL spectroscopy is used to examine and analyze the point defects that occur in Zn-doped GaN. The blue luminescence band seen in undoped and Zn-doped GaN have identical fine structure …

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Electrical And Optical Characterization Of Si-Ge-Sn, Merle D. Hamilton Mar 2012

Electrical And Optical Characterization Of Si-Ge-Sn, Merle D. Hamilton

Theses and Dissertations

The electrical characterization of boron-doped p-Si0.08Ge0.90Sn0.02/p-Ge(100) and p-Si0.112Ge0.86Sn0.028/n-Si(100) with various epilayer thicknesses was measured using the Hall effect. The room temperature sheet carrier concentration ranged from 1.21 x 1013 – 1.32 x 1016 cm-2. The room temperature mobilities were measured to be between 166 and 717 cm2/V·s, depending on sample composition. In the low temperature regime, the mobility was mainly affected by ionized impurity scattering. In the high temperature regime, the mobility was mainly affected by …

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Bis Photobase Generator, Hoang Tran, Shankar B. Rananavare Aug 2011

Bis Photobase Generator, Hoang Tran, Shankar B. Rananavare

Chemistry Faculty Publications and Presentations

The extension of 193nm technology is desirable due to the magnitude of past investments. Since “optical” advancements are increasingly difficult, there is a strong demand for more sophisticated “smart” resists to increase pattern density. Many studies have proven double pattering can be used for the extension of 193nm lithography. In this study, a new class of two stage photo base generators will be introduced along with the synthetic procedure and molecular characterization. The characterizations for exposure study by NMR have shown typical characteristics to stage decomposition under the exposure of 254nm light as well as promising pitch division. GCMS was …

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Synthesis And Characterization Of N- And P- Doped Tin Oxide Nanowires, Hoang Tran, Shankar B. Rananavare Aug 2011

Synthesis And Characterization Of N- And P- Doped Tin Oxide Nanowires, Hoang Tran, Shankar B. Rananavare

Chemistry Faculty Publications and Presentations

Bulk-scale synthetic methods for preparing doped tin oxide (SnO2) nanowires (NWs) are presented. n-and p-doping is achieved through insertion of Antimony and Lithium in tin oxide lattice, respectively. We also present a comparison of the structural and optical properties of SnO2 nanoparticles (NPs), and SnO2 NWs. Both n-type and p- type NWs display a characteristic red shift in their photoluminescence (PL) spectra. Surface plasmons observed in these systems imply high carrier concentrations. These corrosion resistant materials are useful in fabricating ultra-sensitive gas detectors and transparent electronics.

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Synthesis Of Ald Zinc Oxide And Thin Film Materials Optimization For Uv Photodetector Applications, Kandabara Nouhoum Tapily Apr 2011

Synthesis Of Ald Zinc Oxide And Thin Film Materials Optimization For Uv Photodetector Applications, Kandabara Nouhoum Tapily

Electrical & Computer Engineering Theses & Dissertations

Zinc oxide (ZnO) is a direct, wide bandgap semiconductor material. It is thermodynamically stable in the wurtzite structure at ambient temperature conditions. ZnO has very interesting optical and electrical properties and is a suitable candidate for numerous optoelectronic applications such as solar cells, LEDs and UV-photodetectors. ZnO is a naturally n-type semiconductor. Due to the lack of reproducible p-type ZnO, achieving good homojunction ZnO-based photodiodes such as UV-photodetectors remains a challenge. Meanwhile, heterojunction structures of ZnO with p-type substrates such as SiC, GaN, NiO, AlGaN, Si etc. are used; however, those heterojunction diodes suffer from low efficiencies. ZnO is an …

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Investigation Of Yag:Ce Scintillating Fiber Properties Using Silicon Photomultipliers, Bradley S. Jones Mar 2011

Investigation Of Yag:Ce Scintillating Fiber Properties Using Silicon Photomultipliers, Bradley S. Jones

Theses and Dissertations

The properties of thin, cerium activated, yttrium aluminum garnet (YAG:Ce), scintillating fiber-shaped crystals were investigated for particle tracking and calorimetric applications such as Compton imaging of Special Nuclear Material from remote platforms at standoff ranges. Silicon photomultipliers (SiPMs) are relatively new, efficient, single photon sensitive, solid-state photodiode arrays which are well suited for the readout of scintillating fibers. Using SiPMs, the scintillation decay time profiles of six 400 micrometers YAG:Ce fiber crystals were measured under alpha and gamma irradiation. Interestingly, the observed decay times in the thin fibers were substantially slower than values for bulk single crystal YAG:Ce reported in …

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Electron-Phonon Interactions And Quantum Confinement Effects On Optical Transitions In Nanoscale Silicon Films, Vimal Kumar Kamineni Jan 2011

Electron-Phonon Interactions And Quantum Confinement Effects On Optical Transitions In Nanoscale Silicon Films, Vimal Kumar Kamineni

Legacy Theses & Dissertations (2009 - 2024)

Theoretical studies have attributed the temperature dependence of the linear optical response (dielectric function) of bulk semiconductors to electron-phonon interactions and thermal expansion of the lattice. However, the role of phonons in the optical properties of nanoscale structures is often overlooked. This thesis systematically investigates the impact of both carrier confinement and electron-phonon interactions using nanoscale films of silicon in crystalline silicon quantum wells (c-Si QW). Spectroscopic ellipsometry (SE) is a linear optical technique used to of extract the dielectric function and thickness of very thin films. X-ray reflectivity (XRR) was used as the complementary thickness metrology method. The dielectric …

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Optical Characterization Of Fe^{3+} Doped Cds Nanoparticles Synthesized By Wet-Chemical Route, Seyed Mohammad Taheri Otaqsara, Mohammad Hassan Yousefi, Ali Azam Khosravi Jan 2011

Optical Characterization Of Fe^{3+} Doped Cds Nanoparticles Synthesized By Wet-Chemical Route, Seyed Mohammad Taheri Otaqsara, Mohammad Hassan Yousefi, Ali Azam Khosravi

Turkish Journal of Physics

Fe^{3+} doped CdS nanoparticles using Mercaptoethanol as a capping agent were prepared by colloidal wet-chemical method. UV-VIS spectra show that Fe-doping can effectively tune energy band structure, i.e. a large blue shift (\sim 30 nm) with increasing Fe concentration. PL measurement of doped CdS nanoparticles shows an additional emission band at \sim 532 nm, which can be due to radiative transition of dopant level to ground state. X-ray diffraction patterns studies revealed cubic crystal phase. TEM micrographs show a spherical shape and nearly well distribution with an average particle size of \sim 4 nm.

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Metal Contacts On Bulk Zno Crystal Treated With Remote Oxygen Plasma, Z-Q. Fang, B. Claflin, David C. Look, Y. F. Dong, L. Brillson May 2009

Metal Contacts On Bulk Zno Crystal Treated With Remote Oxygen Plasma, Z-Q. Fang, B. Claflin, David C. Look, Y. F. Dong, L. Brillson

Physics Faculty Publications

To study the quality of thin metal/ZnO Schottky contacts (SCs), temperature-dependent current-voltage (I-V), capacitance-voltage, deep level transient spectroscopy, and photoluminescence measurements were performed using bulk, vapor-phase ZnO, treated by remote oxygen plasma (ROP). Au/ZnO and Pd/ZnO contacts on both O and Zn faces are compared as a function of the ROP processing sequence and duration. We find that (i) as the duration of ROP treatment increases from 2 to 4 h, Au/ZnO contacts on the Zn face, deposited before ROP treatment, become rectifying, while those on the O face remain Ohmic; (ii) with long-term ROP …

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Polarity-Related Asymmetry At Zno Surfaces And Metal Interfaces, Y. F. Dong, Z-Q. Fang, David C. Look, Daniel R. Doutt, M. J. Hetzer, L. J. Brillson May 2009

Polarity-Related Asymmetry At Zno Surfaces And Metal Interfaces, Y. F. Dong, Z-Q. Fang, David C. Look, Daniel R. Doutt, M. J. Hetzer, L. J. Brillson

Physics Faculty Publications

Clean ZnO (0001) Zn- and (000(/1)) O-polar surfaces and metal interfaces have been systematically studied by depth-resolved cathodoluminescence spectroscopy, photoluminescence, current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy. Zn-face shows higher near band edge emission and lower near surface defect emission. Even with remote plasma decreases of the 2.5 eV near surface defect emission, (0001)-Zn face emission quality still exceeds that of (000(/1))-O face. The two polar surfaces and corresponding metal interfaces also present very different luminescence evolution under low-energy electron beam irradiation. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display not …

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In-Implanted Zno: Controlled Degenerate Surface Layer, David C. Look, Gary C. Farlow, F. Yaqoob, L. H. Vanamurthy, M. Huang May 2009

In-Implanted Zno: Controlled Degenerate Surface Layer, David C. Look, Gary C. Farlow, F. Yaqoob, L. H. Vanamurthy, M. Huang

Physics Faculty Publications

In was implanted into bulk ZnO creating a square profile with a thickness of about 100 nm and an In concentration of about 1×1020 cm-3. The layer was analyzed with Rutherford backscattering, temperature-dependent Hall effect, and low-temperature photoluminescence measurements. The implantation created a nearly degenerate carrier concentration n of about 2×1019 cm-3, but with a very low mobility μ, increasing from about 0.06 cm2/V s at 20 K to about 2 cm2/V s at 300 K. However, after annealing at 600 °C for 30 min, n increased to about 5×10 …

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Practical Enhancement Of Photoluminescence By Metal Nanoparticles, Greg Sun, Jacob B. Khurgin, R. A. Soref Mar 2009

Practical Enhancement Of Photoluminescence By Metal Nanoparticles, Greg Sun, Jacob B. Khurgin, R. A. Soref

Physics Faculty Publications

We develop a simple yet rigorous theory of the photoluminescence (PL) enhancement in the vicinity of metal nanoparticles. The enhancement takes place during both optical excitation and emission. The strong dependence on the nanoparticle size enables optimization for maximum PL efficiency. Using the example of InGaN quantum dots (QDs) positioned near Ag nanospheres embedded in GaN, we show that strong enhancement can be obtained only for those QDs, atoms, or molecules that are originally inefficient in absorbing as well as in emitting optical energy. We then discuss practical implications for sensor technology.

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Ga-Related Photoluminescence Lines In Ga-Doped Zno Grown By Plasma-Assisted Molecular-Beam Epitaxy, Z. Yang, David C. Look, J. L. Liu Feb 2009

Ga-Related Photoluminescence Lines In Ga-Doped Zno Grown By Plasma-Assisted Molecular-Beam Epitaxy, Z. Yang, David C. Look, J. L. Liu

Physics Faculty Publications

Low-temperature photoluminescence (PL) and temperature-dependent Hall-effect (T-Hall) measurements were carried out in undoped and Ga-doped ZnO thin films grown by molecular-beam epitaxy. As the carrier concentration increases from 1.8×1018 to 1.8×1020 cm−3, the dominant PL line at 9 K changes from I1 (3.368–3.371 eV) to IDA (3.317–3.321 eV), and finally to I8 (3.359 eV). The dominance of I1, due to ionized-donor bound excitons, is unexpected in n-type samples but is shown to be consistent with the T-Hall results. We also show that IDA has characteristics of …

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Ultrafast Spectroscopy Of Mid-Infrared Semiconductors Using The Signal And Idler Beams Of A Synchronous Optical Parametric Oscillator, Richard M. Derbis Mar 2008

Ultrafast Spectroscopy Of Mid-Infrared Semiconductors Using The Signal And Idler Beams Of A Synchronous Optical Parametric Oscillator, Richard M. Derbis

Theses and Dissertations

Mid-Wave Infrared (MWIR) semiconductors are of use to the Air Force for several applications. Ultrafast spectroscopy can be used to better quantify the effectiveness of semiconductor opto-electronic devices. The objective of this thesis was to improve the procedure for taking ultrafast, time-resolved measurements of photoluminescence from MWIR semiconductors. Previous work has used a mode-locked titanium sapphire (Ti:Saph) laser to excite the semiconductor sample and to upconvert the photoluminescence from the semiconductor. Work completed in this thesis improved on the techniques developed during previous work. A synchronous Optical Parameter Oscillator (OPO) will be used to convert the Ti:Saph laser (0.830 µm) …

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