THE KEY ROLE OF POLARITY IN THE GROWTH-PROCESS OF (0001)-NITRIDES

A direct method for the determination of the polarity of (0001) wurtzi te GaN films is presented, using a combination of ion channeling and c onvergent beam electron diffraction experiments (CEDE). The samples we re grown by metal organic chemical vapor deposition (MOCVD) on (0001) Al2O3. Depending on the nitridation conditions of the buffer, the samp les are flat or rough. It is found that flat samples are Ga-terminated . The rough samples exhibit numerous pyramidal defects. In that case, a mixture of N- or Ga-terminated domains is put in evidence. These res ults unambiguously demonstrate that the nitride layer quality is close ly related to the control of the polarity from the very first stages o f the growth. (C) 1997 Elsevier Science S.A.