| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 92 === In this article, we analyzed AlxGa1-xN epilayer which was grown by MOCVD system, with the aid of the micro-photoluminescence (μ-PL) and micro-Raman (μ-Raman) systems. Under the microscopy, we observed several types of hexagonal hillocks on the epilayer. They looked like truncated hexagonal pyramids with their sizes from 2 to 16 μm. From theμ-PL spectra, an additional emission peak at (~3.5eV) inside the hillock structure was found, that differs from the near-band-edge emission (~3.6eV) on the plain region. According to the μ-Raman spectra, the E2 mode peak of the hillock is ~570 cm-1 that is red shifted by about 4 cm-1 with respect to the plain region（~574cm-1）. The FWHM of the E2 mode is 5 cm-1 inside the hillock structure, that is slightly narrower than 6 cm-1 on the plain region. The above data suggest that Al concentration on the hillocks may be reduced to cause the additional PL peak.
Besides, from the microanalysis － Energy Dispersion X-ray Spectrometer（EDX）, we found that the Al concentration is about 5∼6％ inside the hillocks, that is less than ∼12％ on the plain region. These results agreed well with PL spectra. However, the results from the Raman spectra（Al concentration is about 4％ inside the hillock and 8％ on the plain region）are lower than those from PL and EDX measurements, because of the strain effect on the E2 mode frequency, that may underestimate the Al concentration.
Based on our measurements, the optical characteristics of hillocks are attributed to the Al concentration variation, but not contributed from transitions involving defect levels as suggested previously.
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