Abstract
AbstractFor the achievement of high‐efficiency AlGaN‐based deep‐ultraviolet (DUV) light‐emitting diodes (LEDs), we investigated the characteristics of AlN crystal growth depending on m‐ and a‐axis oriented off‐angle of c‐sapphire substrate. In order to reduce threading dislocation density (TDD) in AlN crystal growth, we used ammonia (NH3) pulse‐flow multilayer (ML) growth technique in the metal‐organic chemical vapor phase deposition (MOCVD). We found that a macrostep geometry (large step‐bunching) is generated on the surface of AlN template grown on m‐axis oriented (0001) sapphire substrate. On the other hand, macrostep‐free surface can be obtained for AlN grown on a‐axis oriented sapphire. We also found that cracks are easier generated in AlN grown on a‐axis oriented sapphire. It is considered that step‐flow growth is easily obtained for the growth of a‐axis oriented case due to that the atom site of the step edge in the growth is more stable. On the other hand, for m‐axis oriented case, step‐bunching is considered to occur because atoms are easily drifted during the growth due to that the atom site of the edge steps are more unstable. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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