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Keywords:

  • AlGaN;
  • deep-UV LED;
  • AlN;
  • off-angle;
  • MOCVD;
  • sapphire;
  • macrostep

Abstract

For 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)