Achievement of polarity reversion from Al(Ga)-polar to N-polar for AlGaN film on AlN seeding layer grown by a novel flow‐modulation technology

Abstract

N-polar AlGaN epi-layer was realized on AlN seeding layer grown with a novel flow-modulation method. The polarity reversion from Al(Ga)-polar to N-polar for AlGaN/AlN films was confirmed by KOH etching and subsequent observation with optical microscope as well as high-resolution X-ray diffraction (HR-XRD) measurement. In particular, the dependence of crystalline quality and defect size in the N-polar AlGaN epi-layers on the Ⅴ/Ⅲ ratio was investigated with HR-XRD and scanning electron microscopy (SEM). It was found that as the full width at half maximum (FWHM) value of the X-ray rocking curve (XRC) varied with the Ⅴ/Ⅲ ratio in a "W-shape" for the N-polar AlGaN epi-layers, and a FWHM value as small as 450 arcsec was achieved for the sample grown with a V/III ratio of 988. Moreover, it was revealed by the SEM measurement that the maximum diagonal length of hexagonal cone on the surface of the N-polar AlGaN epi-layers decreased sharply when a Ⅴ/Ⅲ ratio of 1,236 was used although the crystalline quality and the surface morphology of the N-polar AlGaN epi-layers were not improved simultaneously. The peculiar migration of the group-III atoms on the surface of the N-polar AlGaN epi-layer associated with the molar ratio of TMA/(TMA+TMG) was considered to be 2 responsible for this result.

Development of a New Solution Growth Method for AlN Single Crystals Using Type 430 Ferritic Stainless Steel Flux

“…It should be noted that that the formation of N-polar islands occurred only near the liquid surface (Figure 5b,d), and one possible reason is the N−Al ratio: Zhang et al 34 and Keller et al 35 reported the synthesis of N-polar AlN crystals with high N− Al ratios using metal−organic chemical vapor deposition (MOCVD). In this work, the N−Al ratio is higher than that in other regions due to the adequate nitrogen supply at the N 2 -flux interface, causing the formation of N-polar AlN islands near the liquid level.…”