Abstract
We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively. The optimized NPSS contribute to eliminating almost entirely the threading dislocations (TDs) originating from the AlN/sapphire interface via bending the dislocations by image force from the void sidewalls before coalescence. In addition, reducing the misorientations of the adjacent regions during coalescence adopting the low lateral growth rate is also essential for decreasing TDs in the upper AlN epilayer.
Highlights
Convenient for stable and massive application according to our experiment result
It is clearly noticed that the full width at half maximum (FWHM) value of the (0002) peak decreases from 247 to 171 arcsec as the hole diameter increases from 300 to 650 nm, and the value increases to 245 arcsec when the diameter increases to 800 nm
The FWHM value of the asymmetric (1012) peak presents a similar variation process, i.e., first decreasing from 404 to 205 arcsec, increasing to 410 arcsec, where the narrowest FWHM value 205 arcsec is realized on the 650/1000 NPSS
Summary
In our experiments, when lower V/III molar ratio is used in later stage of the coalescence process on the optimizes 650/1000 NPSS, i.e., decreasing the V/III molar ratio from 500 (the optimized value) to 200 while keeping the other conditions unchanged, there is an obvious increase in FWHM values for both (0002) (~20 arcsec) and (1012) (~50 arcsec) peaks compared to the narrowest FWHM values ever shown, which means a high V/III molar ratio is beneficial to alleviate the issue of misorientations, suggesting that low lateral growth rate is vital for misorientations control in AlN epitaxy on NPSS. The first is process A, where a large number of TDs including screw- and edge- types are generated at AlN/sapphire interface on the un-etched mesas due to the large lattice mismatch When these TDs propagate vertically up into the top epilayers, there should be a great increase in TDD. Reducing misorientations of the adjacent regions during coalescence adopting low lateral growth rate is essential for decreasing TDD in the upper AlN epilayer
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