Growth mode and surface morphology of a GaN film deposited along the N-face polar direction on c-plane sapphire substrate

TLDR: The dependence of polar direction of GaN film on growth conditions has been investigated by changing either the group-V/group-III ratio (V/III ratio) in supplying the source gas or the deposition rate as mentioned in this paper.

Abstract: The dependence of polar direction of GaN film on growth conditions has been investigated by changing either the group-V/group-III ratio (V/III ratio) in supplying the source gas or the deposition rate. GaN films were deposited on a nitrided sapphire by two-step metalorganic chemical vapor deposition. The surface morphology changed from flat hexagonal to pyramidal hexagonal facet with the increase of V/III ratio. However, the polar direction of GaN on an optimized buffer layer of 20 nm thickness was N-face (−c) polarity, independent of both the V/III ratio and the deposition rate. The polarity of the GaN epitaxtial layer can be determined by that of an interface (nitrided sapphire, annealed buffer layer or GaN substrate) at the deposition of GaN epitaxial layer. The higher V/III ratio enhanced the nucleation density, and reduced the size of hexagonal facets. The nuclei, forming the favorable hexagonal facets of wurtzite GaN, should grow laterally along the {1010} directions to cover a room among the facet...

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FIG. 7. Variation of rocking curve FWHM value in GaN~0002! ~circle! and (101̄2) ~triangle! planes deposited under V/III ratios of 15 000~closed symbols! and 30 000~open symbols! on the film thickness measured by fou circle XRD.

FIG. 9. Atomic arrangement of1c and 2c GaN surface structures.~a! and ~c! are c-plane views for1c and 2c GaN, respectively.~b! and ~d! are cross-sectional views along the@112̄0# direction for1c and2c GaN, respectively.

FIG. 10. AFM image (1mm31 mm) of 20 nm GaN buffer layers~a! on non-nitrided and~b! on nitrided sapphire substrate after annealing for min by ramping the temperature up to 1040 °C.

FIG. 2. Dependence of average size of hexagonal facet~left axis! and ratio of flat to pyramidal hexagonal facets~right axis! on V/III ratio from 1000 to 30 000 in the GaN epilayer growth process.

FIG. 4. CAICISS spectra of GaN film on nitrided sapphire substrate de ited under V/III ratios of ~b! 1000 and~c! 21 000. The spectra for~a! 1c GaN and~d! 2c GaN are also included as a reference.

FIG. 5. CAICISS spectra of GaN films on~a! HVPE GaN, and~b! MBE GaN substrate.