Investigation of AlN buffer layers on 6H-SiC for AlInN HEMTs grown by MOVPE

In this paper, the influence of V/III molar flow ratio during AlN growth on SiC on growth mode and in-plane strain is investigated. AlN layers of ∼300 nm thickness were grown by metal-organic vapor phase epitaxy (MOVPE) on semi-insulating 6H-SiC and the V/III ratio was changed from 240 to 8200 on four samples by varying the ammonia flux only. The surface morphology was investigated by atomic force microscopy and a growth mode change from two-dimensional to three-dimensional with increasing V/III ratio was observed. Investigation by X-ray diffraction (XRD) reciprocal space mapping (RSM) shows a strong dependence of the AlN peak position on the V/III ratio indicating a significant change in the lattice constants. Results from micro-Raman spectroscopy measurements verify that the AlN in-plane strain can be converted from tensile to compressive when high V/III ratios are applied. Further, an impact of the AlN properties on coalescence time for subsequently grown GaN was found.