| Summary: | 博士 === 國立臺灣大學 === 光電工程學研究所 === 100 === In this dissertation, we first demonstrate the growth of high-quality GaN nanorods (NRs) on c-plane sapphire substrate by metalorganic chemical vapor deposition with various hole patterns on the templates. With the nano-imprint technique, the selective-area growth leads to the growth of regularly patterned GaN NRs. The growth of GaN NRs starts with a hole-filling process, followed by NR growth with the pulsed growth mode through switching on and off alternatively the TMGa and NH3 flows. Regularly arranged GaN NRs of uniform geometry are formed.
Then, a regularly-patterned, c-axis nitride NR array of quite uniform geometry with simultaneous depositions of top-face, c-plane disc-like and sidewall, m-plane core-shell InGaN/GaN quantum well (QW) structures is formed. The differences of geometry and composition between these two groups of QW are studied with scanning electron microscopy, cathodoluminescence (CL), and transmission electron microscopy (TEM). In particular, the strain state analysis results in TEM observations provide us with the information about the QW width and composition. It is found that the QW widths are narrower and the indium contents are higher in the sidewall m-plane QWs, when compared with the top-face c-plane QWs. Also, in the sidewall m-plane QWs, the QW width (indium content) decreases (increases) with the height on the sidewall. The observed results can be interpreted with the migration behaviors of the constituent atoms along the NR sidewall from the bottom.
Next, the cross-sectional sizes of the GaN NRs and QW NRs of different heights and different hexagon orientations between different hole patterns, including different hole diameters and pitches, are demonstrated. The cross-sectional size of the GaN NRs is controlled by the hole diameter and has little to do with the NR height and pitch. On the other hand, the cross-sectional size of the QW NRs is mainly determined by the NR height and is slightly affected by the hexagon orientation. The cross-sectional size variation of GaN NRs is interpreted by the three-dimensional nature of the formed catalytic Ga droplet. The cross-sectional size variation of QW NRs is explained by the condition of constituent atom supply in the gap volume between the neighboring NRs. Also, the plan-view and cross-sectional CL emission wavelengths, including the whole scale and local measurements, among those samples are compared. The emission wavelength depends on the NR height, cross-sectional size, pitch of the pattern, and hexagon orientation. It involves in the factors of indium incorporation rate and well layer thickness and shows a complicated combination of various affecting factors. Generally speaking, the QW NRs with a shorter QW NR, a larger cross-sectional size, or a larger pitch have a longer emission wavelength. The NRs with the side-by-side hexagon orientation have longer emission wavelengths, when compared with those with the edge-to-edge hexagon orientation.
|
|---|
