We investigate excitonic carrier diffusion in both bulk ZnO and nanorods (NRs). Using time-resolved differential reflectivity spectroscopy, we observe a fast decaying component together with a longer exponential relaxation. In bulk ZnO, we find that the fast decay term (∼1 ps) originates from excitonic diffusion along the growth direction. By probing at both the A and B excitons, we find different diffusion coefficients for each. In ZnO nanorods, the diffusion contribution is missing. We attribute this to two effects: (1) defects in the nanorods substantially slow the diffusion process and (2) excitons in nanorods are generated more uniformly than in bulk.

III-Nitride semiconductors are especially capable for both electronics and optical devices. The capability of the III-Nitride semiconductors as light emitters to extent the electromagnetic spectrum from deep ultraviolet light, throughout the whole visible region, and into the infrared part of the spectrum, is a significant characteristic, making this material indispensable for the areas of light emitting devices. The near and far field characteristics of the GaN samples are studied by affecting the finite-difference time domain (FDTD) technique. The far region spreading characteristics at diverse incident angles are also conferred. In addition, the spreading field would be concentrated and the transmission efficiency could be enhanced by the phase shift caused by the dielectric substrate. The intended of optoelectronic devices fictitious from III-Nitride materials is supported by acquaintance of refractive index and absorption coefficient of these materials.

Researches in the field of III-V semiconductor photonic devices have initiate applications in a number of disciplines including lighting, optical communications and biomedical engineering. One of the limiting factors for getting better the photonic devices is the carrier relaxation time. This is the time obligatory for energetic carriers to cool to the edge of their particular bands in a bulk semiconductor material, or to the bottom of a well throughout inter-and intra-sub-band spreading in a heterojunction structure. From these lower energy states, they can afterwards recombine radiatively in photonic devices. This study exploited the nonlinear optical practice of frequency up conversion to complete time-resolved luminescence spectroscopy on epitaxial bulk GaAs samples to analyse carrier relaxation times in each as a function of excitation irradiance and temperature of the sample. There is no electrons and defect energy level in the energy curve for p-type samples. In this study, we focus on the recombination process of yellow-luminescence, which causes the decrease in emission efficiency. The variation of yellow-photoluminescence spectrum shape and intensity, which is caused by occupation YL centers by electrons and thermal activation processes of energy level transitions of electrons by phonon collision in GaAs. The measurement model 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 p-type semiconductors.