(a)-(d) schematic process flow of the masked sapphire substrate with serpentine channel (cross-sectional view). A, B and C are dimensions of 1st opening, channel length and 2nd opening; (e) plan-view OM image of the masked sapphire substrate.
SEM images of GaN stripes (enclosed in dotted lines) grown out of the channel on the masked sapphire substrate. (a) Without low temperature nucleation step; (b) With 4 min of nucleation time; (c) With 8 min of nucleation time.
Gas phase diffusion model used in the study.
Simulated TMGa concentration distribution from the masked sapphire surface to the top of boundary layer (a) in high-temperature growth step covering the boundary layer up to 200 μm, (b) in high-temperature growth step, detailed information within height of 32 μm.
(a) Top-view optical microscope image of the edge of masked sapphire substrate with polycrystalline GaN grown on the center of Si3N4 mask region. (b) Top-view SEM image of polycrystalline GaN on Si3N4 mask region.
Surface TMGa concentration variation versus the distance from the edge of specific pattern for, (a) the blank sapphire, (b) the masked sapphire substrate with filling factor of 0.1, and (c) the masked sapphire substrate with filling factor of 0.01.
(a) Cross-sectional bright-field TEM images of the GaN grown on the serpentine-channel masked sapphire substrate, and (b)-(e) dark-field STEM images of four typical regions marked as A, B, C, D in (a). Dislocations are marked by the arrows. (f) Top-view SEM images of the GaN film after H3PO4 +H2SO4 solution etching at 160 °C for 60 min.
(a) Cross-sectional SEM image of GaN stripes grown out of the serpentine mask prior to coalescence. Monochromatic CL images (b) at 560 nm, and (c) at 365 nm of the same region as (a). Highly defective regions in the serpentine channel are marked by the arrows. (d) Panchromatic CL image of a GaN strip. CL spectra obtained at different positions indicated in (d) are shown in (e) and (f). (g) Simulated growth rate variation of GaN.
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