| Self-assembled GaN quantum dots (QDs) is a quasi-0-dimensional structure, with quantum confinement effect, which restrain the carrier migrate to the non-radiative recombination centers; with discrete energy levels, which suppress the carrier thermally excitation; with quantized electronic states, which reduce the threshold current density. For the heteroepitaxial AlGaN material, the dislocation density is as high as the order of 109 cm-2, resulting in a low internal quantum efficiency in AlGaN quantum wells. This issue has seriously hindered the development of short wavelength optoelectronic devices, therefore the appearance of GaN quantum dots has injected new vitality into this field. In addition, GaN quantum dots also have significance in the single photon source, infrared detector and memory. But the fabrication process of GaN quantum dots for optoelectronic devices has not been systematically reported yet, and the different devices require different densities and sizes of self-assembled GaN quantum dots.Take into account these issues, the fabrication and related properties of self-assembled GaN quantum dots have been investigated by metal organic chemical vapor deposition. From AlN template to i-AlGaN template to n-AlGaN template, high-quality GaN quantum dots have been grown in different templates; From single layer quantum dots to double-layer quantum dots to multilayer quantum dots, the influence of the various growth parameters on the morphology of GaN quantum dots and luminescence properties; From a single GaN quantum dot active region to ZnO nanorods/GaN quantum dot active region, we work toward the goal fabricating optoelectronic devices based on GaN quantum dots. Some progress has achieved as following:Firstly, GaN quantum dots have been grown by Ga droplet method, and the effects of post-growth annealing process on the morphology, the degree of nitridation and the optical properties of GaN QDs have been studied. The mechanism of GaN decomposition, nucleation, Ga atom migration and evaporation during high temperature annealing in NH3/N2 and NH3/H2 atmosphere have been analyzed. Eventually, we have found that in NH3/N2 atmosphere annealing at 850? can significantly improve the nitridation degree of GaN QDs and luminescence perfomance, while the density of GaN quantum dots is reduced to 6.1×109 cm-2.Secondly, the influence of various growth parameters in S-K method on the morphology of GaN quantum dots and their internal mechanism has been studied. By adding the growth interruption the GaN quantum dots with uniform size, high density (2.25×1010cm-2) and excellent optical performance have been obtained even at high temperature.Thirdly, for the first time the two-step growth technique has been introduced in the AlN caplayer, which can effectively reduce the surface roughness and the dislocation density and significantly improve the luminescence properties of GaN quantum dots. Using the two-step AlN interlayer structure, the multilayer stack of GaN/AIN quantum dots with excellent optical performance has been successfully fabricated.Fourthly, GaN quantum dots have been grown on the i-Al0.5GaN and n-Al0.5GaN template via S-K method. Based on the two-step n-Al0.5GaN interlayer, multilayer GaN/n-Al0.5GaN quantum dots with excellent optical performance have been successfully fabricated, which means the active region of GaN quantum dots has been obtained.Fifthly, for the first time GaN quantum dots have been employed as the seed layer of ZnO nanorods. The density of the ZnO nanorods can be well tunable by adjusting the density of GaN QDs. The zero dimensional structure and one dimensional structure have been combined, improving the crystal quality of the heterojunction interface and increasing the injection efficiency, which means the active region of ZnO nanorods/GaN quantum dots has been obtained. |
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