Comparative study of GaN layers grown on insulating AlN and conductive AlGaN buffer layers

The metal-organic vapour phase epitaxy (MOVPE) growth of GaN on 6H-SiC with a conductive AlGaN buffer layer has been studied. With only 6% Al incorporation, a continuous 200 nm thick AlGaN layer n-type doped in the 10¹⁸ cm^-3 range was obtained. A crack-free 1.5 µm thick GaN layer was subsequently grown. The conductivity of the buffer was checked by I(V) measurements with Ni/Au contacts deposited on the back of SiC and on the GaN surface. The layer exhibits strong low temperature (10 K) band edge luminescence at 3.465 eV related to donor bound exciton with a ratio to deep level about 10³ and an FWHM of 3.6 meV. Only threading dislocations are evidenced by TEM with a density of ~10⁹ cm^-2. The FWHM of the (0002) line of GaN in rocking curve scan by x-ray diffraction is 150 arc sec. These properties are similar to the ones of GaN layers deposited on an insulating AlN buffer layer.