| Summary: | 碩士 === 國立交通大學 === 電子物理系 === 91 === We have studied the hexagonal-hill defect ( Hillock base : 1 to 10 μm) of AlGaN films in this thesis. Here, Hillocks were characterized by micro-photoluminescence (μ-PL, spot size : ~1.5 μm) and atomic force
microscopy (AFM, spatial resolution : ~2 nm ) .There are two types of samples in our study, both their Al contents are about 11.0 %. One is pure AlGaN film (Sample A), the other is AlGaN film with GaN dots on it (Sample B). From AFM images, we find that Hillock is a hexagonal pyramid truncated on the (0001) face and with side facets of the pyramid are . However, the top cross-section (0001) is not a perfect plane, but with six slanting planes. In room-temperature μ-PL spectra, Hillocks show a special optical transition ( IH : ~3.49 to 3.59 eV ) which is different from the near-band edge transition ( Inbe : ~3.63 eV ) from the flat region. For sample B, the GaN’s emission (IGaN) from Hillock(~3.40 eV) and flat region(~3.42 eV) also appears at different peak positions. Furthermore, IH has four times higher emission intensity and narrower linewidth (~50 meV) than Inbe (~80 meV) on flat region .Thus, Hillock is an effective defect for optical emission. From low-temperature μ-PL spectra, we also observed the familiar “S-shape” with a characteristic temperature TC~120K ( k TC ~12 meV) which is the same as that of Inbe in typical AlGaN bulks. By applying the Arrhenius model, a localization energy of Eloc ~11.4 meV is obstained.
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