| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 103 === In this study, the InxAl1-xN epilayers have been grown on GaN templates by metalorganic chemical vapor deposition (MOCVD). Several growth conditions consisting of the deposition pressure, the amount of superlattice pairs, and the TMIn flow rate were modified to investigate their effects on the characteristics of InxAl1-xN epilayer. To eliminate the compressive strain generated in the InxGa1-xN multiple quantum well, the InxAl1-xN was used as a quantum barrier. As the composition of InxAl1-xN was varied, the band gap and the lattice constant of this material both were changed in a large range. Therefore, by adjusting the In content of InxAl1-xN, the lattice constant of InxAl1-xN could be the same with that of InxGa1-xN. In this research, the In0.15Ga0.85N was used as a quantum well, while the In0.3Al0.7N was employed as a quantum barrier. This is attributed to the same lattice constant of these two materials.
With increasing the deposition pressure from 100 to 500 mbar, the growth rate of InxAl1-xN epilayer was decreased from 0.402 to 0.094 μm/hr. Meanwhile, the In content of InxAl1-xN was increased from 6.1% to 25%. To improve the quality of InxAl1-xN epilayer, the InGaN/GaN superlattice was inserted between the GaN template and the InxAl1-xN epilayer. It was found that the In content of InxAl1-xN was increased from 22.3% to 43.7% with increasing the InGaN/GaN superlattice from 0 to 20 pairs, and the quality of InxAl1-xN epilayer was also enhanced. However, when the insertion of InGaN/GaN superlattice was more than 5 pairs, the quality of InxAl1-xN epilayer became worse. On the other hand, the reduction in TMIn flow rate can lead to the decreases both in the In content and the growth rate of InxAl1-xN. With decreasing the TMIn flow rate from 220 to 100 sccm, the growth rate of InxAl1-xN was reduced from 0.246 to 0.095 μm/hr. Additionally, as the TMIn flow rates were kept at 220, 180, 140, and 100 sccm, the root-mean-square roughness values of InxAl1-xN surface were measured to be 5.70, 8.11, 7.73, and 5.57 nm, respectively.
Furthermore, the APSYS software was used to simulate the performance of blue LED with the In0.3Al0.7N quantum barrier. The lattice match between the In0.3Al0.7N quantum barrier and the In0.15Ga0.85N well can reduce the piezoelectricity of In0.15Ga0.85N well due to the reduction of residual strain in the multiple quantum well. Thus, the emission wavelength of LED device can be predicted to blue shift as the In0.3Al0.7N quantum barrier was inserted. Finally, the simulated LED structure was prepared by MOCVD. Based on the result of photoluminescence spectrum, it can be observed that the LED without inserting the In0.15Ga0.85N/In0.3Al0.7N superlattice possessed two emission peaks at 380 and 460 nm, and the intensities of these two peaks were both weak. However, the LED with the In0.15Ga0.85N/In0.3Al0.7N superlattice had only one emission peak at 400 nm, and its intensity was much higher than that without this superlattice. It can be confirmed that the InxAl1-xN with an improved quality can be useful in the LED epitaxial structure, causing an efficient enhancement in the emission property.
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