| Summary: | 碩士 === 國立交通大學 === 光電工程系所 === 93 === In this thesis, two kinds of nanostructure samples grown by metalorganic chemical vapor deposition were studied. We utilized the photoluminescence (PL), photoluminescence excitation (PLE) to investigate the optical properties of our samples. The first series are In0.4Ga0.6As1-xNx/GaAs single quantum well structures with different nitrogen concentrations and the second ones are the InGaN/GaN quantum dots samples with different sizes.
InGaAsN SQWs with various nitrogen concentrations, where x=0, 0.5 and 2%, were grown on GaAs substrates. The effects of incorporating nitrogen into the In0.4Ga0.6As1-xNx/GaAs SQW were investigated using photoluminescence (PL) and high resolution transmission electron microscope (HRTEM). In the case of In0.4Ga0.6As1-xNx SQW with 2% nitrogen content, the PL emission from the quantum-dot-like states was observed and confirmed by the temperature- and excitation-dependent PL measurements. Detailed investigations conducted here indicate that the nitrogen not only influences carrier localization, but also is critical in the formation of quantum-dots.
In the second part, we investigate the optical properties of ultra-high-density InGaN quantum dots (QDs). Atomic force microscopy revealed that the extremely high density about 3×1011 cm-2 of QDs was obtained and the size of QDs was increased with the duration of SiNx treatment. The PL-peak wavelength at 10K of the InGaN QDs samples is red-shifted as increasing the height of QDs. From the temperature dependence of the photoluminescence, the thermal activation energy (Ea) exhibited different activation energies for large and small QDs. Ea of the smaller QDs samples is about 59meV, much less than that of the largest QDs, 122 meV. In addition, the PLE spectra broadened with increasing the height of QDs.
Finally, we study the effects of rapid thermal annealing on optical properties of InGaN QDs with the SiNx treatment time. Their behaviors were investigated through temperature- dependent photoluminescence measurements. The results indicated that emission wavelength of the InGaN QDs shifted toward long wavelength after the post-thermal annealing, which may be due to In/Ga inter- diffusion and variation on the QDs size by post-grown thermal annealing.
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