| Summary: | 博士 === 國立交通大學 === 電子物理系所 === 98 === In this dissertation, the use of preheating ammonia installation can be used to increase the thermal decomposition efficiency of ammonia, we have demonstrated that the entire composition of InxGa1-xN epilayers prepared by MOCVD can be achieved merely by varying the growth temperature and In vapor mole fraction. First, the In solid composition, as anticipated, was increased from 0.14 to 0.40 as the growth temperature decreased from 750 to 650 oC, which corresponds to a wavelength can be extends to the 738 nm in the deep red region with linewidth 180 meV. Further, as input In vapor mole fraction raise to 73 %, we could estimate that the In solid composition of the InxG1-xN films increases to 0.44, which corresponds to a wavelength range extend to near infrared 950 nm with linewidth 235 meV. Therefore, we have surmounted the technique bottleneck of the absence of entire composition of InGaN epilayers, especially the emission wavelength 650-1100 nm.
For samples grown at temperature > 700 oC, separated by about 500 meV, two emission peaks are observable. The corresponding emission peaks, namely high and low emission peaks, are shift from 2.94 to 2.58 eV and from 2.44 to 2.07 as the growth temperature decrease from 750 to 700 oC. The high peak energy originates from strained layer closer to GaN buffer and low energy from relaxed layer near the surface, as revealed by the results of high-resolution x-ray reciprocal space mapping (RSM) and cathodoluminescence (CL) measurements. For samples grown at temperature < 700 oC, high In content epilayers having a large lattice mismatch with under GaN buffer layer, the nearly absence of strained layer resulting in the feature of single emission peaks in both PL and CL spectra. In order to further extend the wavelength of the InGaN epilayer, we grew the InGaN sample at a growth temperature of 650 oC, in an attempt to investigate the dependence of InGaN solid composition on input In reactant flow rate. For the In solid composition, we thought that too high the TMIn flow rate will lead to decrease of In concentration solid, unfavorable to the high In content InGaN growth. Besides, we also reveals that the 14-K photoluminescence peak energy of InGaN epilayers exhibit a wide emission tunability from 2.75 to 1.29 eV, covering a wavelength ranges from blue, green, red and even reaches infrared 960 nm spectrum region. It shown that the bowing parameter of b ~ 2.3 eV for our results and the literature data for the band gap of InxGa1-xN over the entire composition. Our observation provides conclusive evidence that the InxGa1-xN epilayers exhibits a larger Stokes shift, showing that the alloy’s inhomogeneity.
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