| Summary: | 博士 === 國立交通大學 === 電子物理系所 === 96 === This thesis elucidates the macroscopic and microscopic electrical properties of the GaN epilayer. First, Si-modulation doping layers (Si-MDLs)are used to reduce the dislocation density to less than 108 cm-2 and improve electron mobility to 322 cm2/V-s Analysis of temperature-dependent mobilities indicates in the high dislocation regime, the electron transport is limited by charged threading dislocations. In the low-dislocation regime, electrons more easily collide with point defects as short-range scattering centers. The consistency between the estimated density and that determined by deep level transient spectroscopy (DLTS) reveals that the short-range scattering centers may be nitrogen interstitial with an energy level at EC-1.01�b0.09 eV. On the other hand, conductive atomic force microscopy reveals the spatially resolved current distribution around a V-defect. The current intensity in the V-defect is three orders of magnitude higher than in the surrounding regions. Further static current-voltage measurement suggests that the current flow is governed by Schottky emission and Fowler-Nordheim tunneling in the V-defect region and in the surrounding area, respectively.
Flow-rate modulation epitaxy (FME) is utilized herein to fabricate InN nanostructures. At 600℃ with low background NH3 flows of 250 sccm during the In step with an NH3 flow rate that exceeds 1500 sccm in the N-step prevents the generation of droplets and optimize quality. The FME growth mode has the advantage that the growth efficiency is not suppressed, even for an effective V/III of 60000, unlike the situation in the conventional mode, in which the growth rate is reduced by 75% when V/III exceeds 30000. Together with the sustained photoluminescence efficiency, which peaks at 0.75 eV, this result reveals that FME suppresses the formation of stacking faults of nitrogen atoms in the high-V/III-ratio regime.
Finally, a series of InN dots was fabricated at 700℃ by metalorganic chemical vapor deposition (MOCVD) with repetitive interruptions of group-III precursor. Interruption time of each cycle exceeds 15s under NH3 ambient result in a successful removal of indium droplets at elevated growth temperature and is probably explained by a converting into InN. As for droplet-free InN samples, photoluminescence (PL) spectra revealed ~0.70 eV emissions with linewidth of ~60 meV. Based on the time-resolved PL measurements (TRPL), the 0.70 eV emissions are probably correlated with holes localized at deep level states near valance band, in which is in coincident with In vacancies nearby embedded indium clusters.
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