Journal
VACUUM
Volume 217, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.vacuum.2023.112553
Keywords
GaN; Magnetron sputtering; HiPIMS; Dislocations; XRC; TEM
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By using a high-quality AlN buffer layer, the threading dislocation density of sputtered GaN films can be reduced, leading to an improvement in the crystal quality of GaN.
Gallium nitride (GaN) epitaxial films on sapphire (Al2O3) substrates have been grown using reactive magnetron sputter epitaxy with a liquid Ga target. Threading dislocations density (TDD) of sputtered GaN films was reduced by using an inserted high-quality aluminum nitride (AlN) buffer layer grown by reactive high power impulse magnetron sputtering (R-HiPIMS) in a gas mixture of Ar and N2. After optimizing the Ar/N2 pressure ratio and deposition power, a high-quality AlN film exhibiting a narrow full-width at half-maximum (FWHM) value of the double-crystal x-ray rocking curve (DCXRC) of the AlN(0002) peak of 0.086 & DEG; was obtained by R-HiPIMS. The mechanism giving rise the observed quality improvement is attributed to the enhancement of kinetic energy of the adatoms in the deposition process when operated in a transition mode. With the inserted HiPIMS-AlN as a buffer layer for direct current magnetron sputtering (DCMS) GaN growth, the FWHM values of GaN(0002) and (10 1 1) XRC decrease from 0.321 & DEG; to 0.087 & DEG; and from 0.596 & DEG; to 0.562 & DEG;, compared to the direct growth of GaN on sapphire, respectively. An order of magnitude reduction from 2.7 x 109 cm-2 to 2.0 x 108 cm-2 of screw-type TDD calculated from the FWHM of the XRC data using the inserted HiPIMS-AlN buffer layer demonstrates the improvement of crystal quality of GaN. The result of TDD reduction using the HiPIMS-AlN buffer was also verified by weak beam dark-field (WBDF) cross-sectional transmission electron microscopy (TEM).
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