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.

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.

In this thesis, we investigate the OTDR on-line monitoring feasibility of forward- and backward-pumping distributed Raman fiber amplifiers (FRAs) transmission systems with different OTDR probe lights. In the experiments, we choose the large effect area fiber ( LEAF ) with 50 km long as gain medium of Raman amplifiers. Two different OTDR probe lights with 1.31£gm and 1.65£gm wavelengths are separately used for on-line monitoring forward- and backward-pumping distributed FRAs. We find that the OTDR probe lights affect the optical gain of the 1.55 mm data signal. In the experiments, for the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal increases 0.2 dB, but for the backward-pumping scheme, that only increases 0.1 dB. In the forward-pumping scheme using 1.65£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal decreases 0.6 dB, but for the backward-pumping scheme, that only decreases 0.2 dB. We also find the OTDR on-line monitoring distribution fiber Raman amplifiers Systems makes OTDR traces distortion. In an aspect of system BER performance, the system power penalty on account of the OTDR monitoring in both 10 Gb/s forward- and backward-pumping schemes is trivial¡@. In the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the power penalty is about 0.1 dB, but for the backward-pumping scheme that is about 0.05 dB. As the forward-pumping scheme using 1.65£gm OTDR probe light, the power penalty is about 0.2 dB, but for the backward-pumping scheme that is about 0.07 dB.

Generation of reproducible attosecond (10-18s) pulses is an exciting goal: in the same way as femtosecond pulses were used to make "movies" of the atomic motion in molecules, attosecond pulses could "uncover" the motion of electrons around nuclei. In this dissertation, we have suggested new ideas that will allow improving one scheme for obtaining such ultra-short pulses: the molecular modulation technique. In a theoretical proposal called Raman Additive technique, we have suggested a method that will allow (with a proper phase stabilization of generated sidebands) to obtain reproducible waveforms of arbitrary shape. An exciting range of possibilities could open up - not only for absolute phase control or sub-cycle shape control, but also for investigation of multiphoton ionization rates as a function of the sub-cycle shape. We have elaborated on the latter subject in another theoretical project, where we have exploited the unique feature of such ultrashort laser pulses, which is synchronization with molecular motion (rotational or vibrational), in order to investigate photoionization of molecules. From experimental point of view, a different construction of driving lasers than previously employed led to establishment of larger molecular coherences at higher operating pressure than in previous experiments. This resulted in simultaneous generation of rotational and vibrational sidebands with only two fields applied. In another experimental proposal using rotational transition in deuterium we have shown that employing a hollow waveguide instead of normal Raman cell improves the efficiency of the generation process. By optimizing gas pressure and waveguide geometry to compensate the dispersion, the method can be extended to efficiently generate Raman sidebands at a much lower energy of driving fields than previously employed. At the end, a very exciting possibility for controlling the molecular motion in a Raman driven system will be shown. Based on the interference effects (EITlike) that take place inside of a molecule, selectivity of different degrees of freedom can be achieved (for example switching from rotational-vibrational motion to pure rotational).

En esta tesis se presenta un estudio por espectroscopía Raman de la calidad estructural del cristal y del comportamiento de los modos acoplados en las aleaciones AlxGa1-xAs dopadas con Silicio. Como se sabe, cuando las impurezas son introducidas en las aleaciones AlxGa1-xAs: Si pueden ser observados los modos acoplados fonón LO-plasmón. La observación de estos modos es posible porque la simetría translacional del cristal es destruida. Como consecuencia, las reglas de selección son violadas o relajadas y las líneas Raman se tornan anchas y asimétricas. El análisis de la posición y la forma de las líneas espectrales nos permite obtener información sobre la concentración de los portadores y los efectos del desorden estructural del material. Se encontró que la concentración efectiva de portadores medida en Raman difiere de la concentración nominal dada por el fabricante. Esto sugiere posibles pérdidas en el proceso de evaporación del Silicio o al exceso de tiempo de evaporación. Los resultados fueron verificados también por medidas de Capacitancia versus Voltaje para dos muestras. Este trabajo muestra la validez de la técnica Raman en el estudio de heteroestructuras semiconductoras en vista de que los modos acoplados fonón LO – plasmón son muy sensibles al desorden composicional de las muestras.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 210-212).

Reproduction de : Thèse doctorat : Physique. Optoélectronique : Metz : 2002. / Titre provenant de l'écran-titre. Notes bibliographiques.

Thèse doctorat : Dispositifs de l'Electronique Intégrée : Villeurbanne, INSA : 2008. / Titre provenant de l'écran-titre. Bibliogr. à la fin de chaque chapitre.

Reproduction de : Thèse de doctorat : Physique : Lyon 1 : 2008. / Titre provenant de l'écran titre. Bibliogr. p. 157-166.

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 164-175).