Montages of SCM phase data for samples with different growth conditions: (a) sample A with 0 s 3D growth, (b) sample B with 600 s 3D growth then coalesced, and (c) sample C with 2400 s 3D growth then coalesced.
Variation in conductive interface layer thickness and top surface rms roughness with 3D growth time.
Quantification of carrier concentration in the conductive interface region: (a) SCM amplitude image of the conductive interface region and the calibration dopant staircase structure, (b) SCM amplitude data from the Si-doped calibration staircase structure is averaged in the slow-scan (vertical) direction to form a line profile, (c) a calibration curve is constructed between log (doping concentration from SIMS) and SCM amplitude data, showing a roughly linear relationship, and the average carrier concentration over the conductive interface region is then estimated, and (d) the carrier concentration decreases along the inclined feature away from the GaN/sapphire interface.
Low temperature (6 K) CL spectrum of sample C in cross section revealing two emission peaks at 3.41 and 3.30 eV, associated with BSFs and PSFs, respectively.
Cross-sectional monochromatic CL images of sample C showing luminescence at (a) 3.41 eV and (b) 3.30 eV, related with BSFs and PSFs, respectively.
Cross-sectional TEM image of sample B viewed along  using . Red arrows indicate PSFs extending at ±60° from the GaN/sapphire interface, and the white dash line indicates the position where dislocation lines change direction.
A summary of growth conditions for samples A–C.
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