Abstract
A three-step growth process is developed for depositing high-quality aluminium-nitride (AlN) epilayers on (001) sapphire by low pressure metalorganic chemical vapour deposition (LP-MOCVD). We adopt a low temperature (LT) AlN nucleation layer (NL), and two high temperature (HT) AlN layers with different V/III ratios. Our results reveal that the optimal NL temperature is 840–880°C, and there exists a proper growth switching from low to high V/III ratio for further reducing threading dislocations (TDs). The screw-type TD density of the optimized AlN film is just 7.86 × 106cm−2, about three orders lower than its edge-type one of 2 × 109cm−2 estimated by high-resolution x-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (TEM).
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