Crack-free Si-doped n-AlGaN film grown on sapphire substrate with high-temperature AlN interlayer

The crack-free Si-doped n-Al0.28Ga0.72N epitaxial films with high-temperature (HT) AlN interlayer were successfully grown on c-plane sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The high resolution X-ray diffraction (XRD) measurement results demonstrate that the density of dislocations was reduced significantly with the insertion of the HT-grown AlN interlayer between the low-temperature (LT)-grown AlN buffer layer and the n-AlGaN epitaxial film. Room temperature (RT) Raman scattering spectra show a blue-shift for the E2 (high) phonon mode, implying that the Si-doped n-Al0.28Ga0.72N epitaxial film is under compressive strain. Moreover, the photoluminescence (PL) peak position slightly red-shifted from 311 to 315 nm, while the PL intensity decreased remarkably as the temperature was increased from 10 to 300 K. The Hall effect measurement results reveal that a carrier density in the Si-doped n-Al0.28Ga0.72N epitaxial film as high as 6.84 × 1018 cm−3 has been achieved.