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Optical properties of GaN and ZnO based thin layers and nanostructures


Author: Victor Zalamai
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2006
Scientific adviser: Ion Tighineanu
doctor habilitat, professor, Institute of Mathematics and Computer Science of the ASM
Institution:

Status

The thesis was presented on the 5 April, 2006
Approved by NCAA on the 29 June, 2006

Abstract

Adobe PDF document0.21 Mb / in romanian
Adobe PDF document0.25 Mb / in russian

Thesis

CZU 621.315.592

Adobe PDF document 2.75 Mb / in russian
174 pages


Summary

The work is devoted to the investigation of the influence of strains and defects upon the optical properties of GaN layers and AIN/GaN heterostructures as well as upon the optical properties of ZnO/opal nanostructures and layer. The mechanisms of excitation of Eu ions introduced in the crystal of ZnO based phosphors are also studied.

It was found that the specific structure and morphology of GaN layers grown on sapphire and 6H-SiC substrates as well as the strains inherent to these layers lead to such phenomena as sharp changes in optical reflectance during the cooling and heating of AIN/GaN heterostructures, persistent photoconductivity, and optical quenching of photoconductivity. The regularities and mechanisms of these phenomena were established. The models and schemes explaining their origin and nature were proposed. The parameters of excitons in GaN layers and their dependence upon the strains caused by large crystal lattice mismatches lattice and thermal coefficients differences between the GaN layers and substrate were determined.

The reasons of degradation of the optical properties of AIN/GaN/sapphire heterostructures at supercritical thicknesses of the A1N film, and the correlation between optical and electrical properties of structures are determined. It is shown, that the degradation results from the cracking of the A1N film, leading to the formation of multiple structural defects. The model of electronic transitions with the participation of defects determining the optical properties of GaN layers in theses heterostructures is proposed.

ZnO/opal nanostructures are prepared. The nature of photoluminescence bands in different opal based ZnO structures is determined. The mechanisms of resonant multi-phonon Raman scattering in ZnO single crystals, layers and nanostructure under the excitation by different laser lines at different temperatures are investigated. The possibility to fabricate efficient phosphors on the basis of ZnO doped by Eu3+ ions is shown. The sites of the Eu3+ incorporation into the ZnO lattice and the mechanisms of their excitation by ultraviolet radiation are determined. The obtained results were published in 15 scientific papers.

The thesis is written in Russian and it consists of 90 text pages, 74 figures, 11 tables and 271 references.