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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Photoluminescence, Photoluminescence Excitation and Absorption of m-GaN

Cheng, Yu-li 22 August 2007 (has links)
Group III nitrides have recently attracted great interest and are intensively studied for that cover continuously from the ultraviolet to nearinfrared region by proper alloying.Therefore, group III nitrides have wide applications inoptoelectronic devices, such as light-emitting diodes,ultraviolet or blue lasers, and full color displays. Unintentionally doped m-GaN thin films have been epitaxially grown on LAO by PAMBE. The optical characteristics were investigated with photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectrum.
2

Photoluminescence Properties of InGaN/GaN Heterostructures Grown on Silicon Substrates

Huang, Chi-huang 03 August 2005 (has links)
In this thesis, we study the structural and optical properties of GaN-based material structures grown on silicon substrates by temperature-dependent Photoluminescence (PL)¡BRaman¡BXRD and time-resolved PL measurements. In non-intentionally doped GaN structure, various excitonic transitions near band edge are observed and identified. We estimate the stress of the GaN samples to be 0.671 Gpa and 0.57 Gpa by using the energy shift of neutral-donor-bound exciton transitions. This is consistent with our Raman measurements. According to the XRD patterns, the length of InGaN/GaN multiple quantum wells in samples D¡BE¡BF are 43.83 nm¡B65 nm and 68.27 nm. In these samples, multiple PL peaks at low temperatures are observed. Carrier recombination lifetime have been measured as well.
3

Studies of Optical properties of Oxide Semiconductor

Cheng, Tian-You 28 July 2006 (has links)
Oxide semiconductors, especially ZnO, have been a subject of considerable research interest due to their interesting optoelectronic properties. Recent researches have shown that one-dimensional ZnO nanowires have characteristics of high stability, good luminescence efficiency, low critical voltage, high radiate current density and durability. In this study photoluminescence (PL) spectroscopy and Raman scattering spectroscopy were utilized to explore the optical properties of ZnO nanowires. The ZnO nanowires were grown on a-plane sapphire substrates by a simple vapor phase transport method without metal catalysts. Such a catalyst-free synthesis can avoid the metal remnants in the nanowires. Room temperature PL measurement showed that the intensity of ultraviolet (UV) luminescence increases as the average diameter of ZnO nanowires decreases. Such an observation is quite different from the reported PL data of nanowires grown with the use of catalysts. Moreover, an ¡§anomalous¡¨ redshift of the UV peak position with diminished wire diameter was observed. We attribute this redshift to the effects caused by the laser heating. The full-width at half maximum (FWHM) of the UV luminescence from the ZnO nanowires was found to decrease with better uniformities of wire distribution, alignment, and diameter. In addition, the ratio of UV to green emission integrated intensities becomes higher as the FWHM of the UV peak decreases. Thus the FWHM of the UV luminescence seems to be a measure of the uniformity and crystallinity (defects) of ZnO nanowires. Temperature-dependent PL and Varshni relation fitting results show the center position of UV luminescence is 3.29 eV for ZnO nanowires, and 3.24 eV for ZnO buffer layer structures. The Raman spectroscopy and SEM studies showed that the samples with randomly oriented nanowire structures exhibit the A1(LO) and E1(LO) vibrating modes.
4

Investigation of AlGaN/GaN Heterostructure Using Photoluminescence

Chang, Hsien-Cheng 02 July 2007 (has links)
We study AlGaN/GaN heterostucture using temperature dependent micro-photoluminescence. Detailing its principle, operation process and analysis is to provide usage experiences for posterity's reference. The experiment's results emphasize analysis in the photoluminescence spectrum of the GaN in the heterostructure. We believe the peaks 3.486eV, 3.405eV and 3.310eV provided from Free Exciton A, FXA-1LO and FXA-2LO respectively by experience in the cultural heritage.And the fitting result of FXA peak with Gaussian curve shows the major peak is composed by (D0,X), FXA and FXB. Finally, we analyze the major peaks' characteristics varied with the temperature.
5

The Study of Carrier Relaxation in Multi-Stacked InAs/GaAs Quantum Dots

Lu, Shu-kai 11 August 2006 (has links)
Carrier dynamics of mullti-stacked quantum dots (MSQDs) have been studied by means of time-integrated and time-resolved photoluminescence (PL). The MSQD with different spacer thickness of 10, 15, 20 and 30 nm were grown by molecular beam epitaxy. Time-integrated PL exhibit red shift as spacer thickness increases. The red shift originated from the vertical coupling relaxes the strain in the MSQDs, leading to a decrease in the PL peak energy. From time-resolved PL, the MSQD with spacer thickness increased reveals the shorter lifetime of PL peak among samples studies. We attribute the maximum of lifetime to a better vertical alignment. We report on a measurement of the rise and decay of luminescence intensity in the MSQDs excited at 1.54 eV (808 nm) and 3.09 eV (404 nm). The results show a slow rise time of electrons from the L to the £F valley for high photoexcitation energies. The decay in luminescence is longest with photoexcitation at 3.09 eV, we demonstrate the importance of the penetration depth and carriers tunneling. In addition, the MSQDs strongly depends of on the carrier injection. The rise times decrease with increasing excitation density. The properties are characteristic features of Auger processes.
6

PL/SQL till Java : Konvertering med verktyg / PL/SQL to Java : Conversion with tools

Sköld Martini, Fredrik, Axell, Philip January 2012 (has links)
Den här rapporten hanterar ett uppdrag från företaget Logica gjort som ett examensarbete på utbildningen Högskoleingenjör inom Datateknik, programmet Webbutveckling/Programmering och datanät, på Tekniska Högskolan i Jönköping. Uppdraget gick ut på att kontrollera om ett system skrivet i programmeringsspråket PL/SQL går att konvertera till Java. Programmet i fråga var ett reskontrasystem. Syftet med projektet var att företaget skulle kunna konvertera deras system på ett så kostnadseffektivt och tidsbesparande sätt som möjligt. Frågor som rapporten har tagit upp är huruvida det finns konverteringsverktyg som kan göra detta och om i så fall det finns några “Best-practises” angående detta. Vi har undersökt detta genom informationssökning om olika verktyg samt om de båda språken. För att verifiera de olika verktygens funktionalitet har ett antal olika tester med konvertering utförts. De tester som har genomförts visar på att en konvertering mellan PL/SQL och Java kan fungera, men då under standardiserade former. Till denna kategori hörde dock inte Logicas applikation, som förlorade all sin funktionalitet under processen i ett av testen och genereringen av användbar kod var minimal. Vi kom fram till att i det här fallet var en konvertering ej möjlig att rättfärdiga i ett kostnadsperspektiv.
7

Investigation of SiOxNy Thin Films with Photoluminescence, Raman, and Capacitance-Voltage Measurements

Chou, Shu-Ting 16 June 2003 (has links)
ABSTRACT As MOSFET getting smaller, its silicon dioxide reaches physical limit. To continue its insulation and reasonable interface defects density, now, SiOxNy is the replace material to fill the transition term between SiO2 to high-k material. SiOxNy is made from silicon dioxide and silicon nitride in different scale. Due to the uncompleted of bonding, the device¡¦s reliability is dependent on defects. The discussion about defects will help us to change the growth conditions in process and avoid to produce these defects. We use PL and Raman spectrum to study the defects in SiOxNy and compare them under different process conditions especially on the change of defects. PL result on 6.2 nm film have a peak at 390 nm, and 40 nm film have peak at 535 nm. This mean that under these two process conditions the defect correspond to 3.18 eV is . The defect correspond to 2.37 eV is . In this thesis, we report formulations of how to calculate the parameters of MOS structure, using SiON/p-Si MOS structure as calculated sample. The carrier concentration were calculated and compared with the Hall results. The flat band voltage and threshold voltage were calculated and compared with measured C-V curves.
8

The Effect of Annealing on the Optical Properties of Zinc Oxide

Neiman, Alex January 2014 (has links)
Photoluminescence spectroscopy of bulk zinc oxide under different annealing conditions was examined. The effect of the annealing atmosphere, temperature and time on the optical properties of zinc oxide were studied to investigate the influence on the intrinsic defects present. The wafers used were bulk +c ZnO grown by Tokyo Denpa using the hydrothermal technique. The annealing effect on both zinc and oxygen faces was investigated. The dominant donor bound exciton related to aluminum, labelled in the literature as I₆ demonstrated a splitting of 0.3 meV. The origin of this splitting has been linked to an interaction between aluminum and hydrogen, through its reaction to atmospheric dependent annealing. The removal of the hydrothermal hydrogen peak at 3.3624 eV has uncovered some fine structure. After Arrhenius analysis of this fine structure it was shown it is excited states of bound excitons. This fine structure has been loosely associated with vibrational and rotational excited states. The behaviour of all the optical features present in the photoluminescent spectra under annealing has a relation with the carrier concentration of the samples.
9

Growth and Characterization of ZnO Nanostructures

Syed, Abdul Samad January 2011 (has links)
A close relation between structural and optical properties of any semiconductor material does exist. An adequate knowledge and understanding of this relationship is necessary for fabrication of devices with desired optical properties. The structural quality and hence the optical properties can be influenced by the growth method and the substrate used. The aim of this work was to investigate the change in optical properties caused by growth techniques and substrate modification. To study the influence of growth technique on optical properties, ZnO nanostructures were grown using atmospheric pressure metal organic chemical vapor deposition (APMOCVD) and chemical bath deposition (CBD) technique. The structural and optical investigations were performed using scanning electron microscopy (SEM) and micro photoluminescence (μ-PL), respectively. The results revealed that the grown structures were in the shape of nano-rods with slightly different shapes. Optical investigation revealed that low temperature PL spectrum for both the samples was dominated by neutral donor bound excitons emission and it tends to be replaced by free exciton (FX) emission in the temperature range of 60-140K. Both excitonic emissions show a typical red-shift with increase in temperature but with a different temperature dynamics for both the sample and this is due to difference in exciton-phonon interaction because of the different sizes of nano-rods. Defect level emission (DLE) is negligible in both the sample at low temperature but it increased linearly in intensity after 130 K up to the room temperature.Modification in substrate can also play a significant role on structural and optical properties of the material. Specially variation in the miscut angle of substrate can help to control the lateral sizes of the Nanostructures and thus can help to obtain better structural andoptical quality. Also optical quality is a key requirement for making blue and ultraviolet LEDs. Therefore, ZnO Nanostructures were grown on SiC on-axis and off-axis substrates having different off-cut angles. Morphological investigation revealed thatgrown structures are epitaxial for the case when substrate off-cut angle is higher and deposition rate is low. Low temperature PL spectrum of all the samples was dominated by neutral donor bound excitons and free exciton emission become dominant at 100 K for all the samples which completely eliminate the neutral donor bound excitonic emission at 160K. Two electron satellite of the neutral donor bound excitons and LO phonons of excitonic features are also present. A typical red-shift in excitonic features was evident in temperature dependence measurement. Red-shift behavior of free exciton for all the samples was treated by applying Varshni empirical expression and several important parameter, such as, the Debye temperature and the band gap energy value was extracted. Thermal quenching behavior was also observed and treated by thermal quenching expression and value of the activation energy for non-radiative channel was extracted. The results that are obtained demonstrate a significant contribution in the fields of ZnO based nano-optoelectronics and nano-electronics.
10

Strategiarbete och legitimitetens påverkan : En fallstudie hos Greenpeace

Jakobsson, Birgitta, Nitz, Cajsa January 2015 (has links)
When an organization is doing strategic planning, it should take into consideration the different perspectives within the planning process, as well as the various methods available to construct a strategy. Research by Mintzberg and Waters shows that strategy planning ranges on a scale of completely deliberate to completely emergent. Deliberate strategies are well thought out and well planned in order to reach a specific goal. From the beginning of the process, there is no doubt what the desired outcome is and everyone in the organization shares the same goal. Emergent strategies are the opposite of deliberate strategies. With an emergent strategy, the strategy develops over time and actions are taken without an end goal in mind. The strategies and campaigns used by Greenpeace are known across the world and the organization's relatively bold way of pursuing its goals is presumed to require a certain measure of legitimacy to succeed. The purpose of this study is to determine if Greenpeace is working using deliberate or emergent strategies, as well as what role the legitimacy of the organization plays in the development of those strategies. The study has been conducted by doing a qualitative case study of Greenpeace. Two respondents from the head office in Stockholm were interviewed and data from a documentary and several campaigns were analyzed. / När en organisation lägger upp strategier och tar strategiska beslut finns det olika perspektiv och sätt att bygga upp strategierna på. Forskning gjord av Mintzberg och Waters visar att arbetet med strategier befinner sig på en skala mellan helt planerade (deliberate) och helt framväxande (emergent). Planerade strategier är genomtänkta och väl planerade inför ett specifikt mål. Det har inte varit några tvivel om vadsom var önskat innan man genomförde sina handlingar och alla i organisationen delar samma mål. Framväxande strategier har de motsatta egenskaperna i form av att strategin gradvis träder fram och handlingarna sker utan att det från början har funnits någon specifik avsikt med handlingen. Strategierna och kampanjerna hos organisationen Greenpeaceär kända världen över och dessrelativt utmanande sätt att arbeta kan antas kräva legitimitet från omgivningen för att arbetet ska kunna genomföras och lyckas. Syftet med undersökningen är därför att undersöka om Greenpeace arbetar med planerade eller framväxande strategier, samt vilken roll desslegitimitet spelar för framtagningen av dessstrategier. Studien har genomförts med hjälp av enkvalitativ fallstudie i Greenpeace. Två respondenter från huvudkontoret i Stockholm har intervjuats och data från en dokumentär om Greenpeace samt om kampanjer har analyserats. Undersökningens empiri visar att Greenpeaces strategier har tendenser för både planerade och framväxande strategier. Vi menar dock att strategierna ligger närmare planerade än framväxande.

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