Scanning photoelectron microscopy study of as-grown and heat-treated chemical vapor deposition boron-doped diamond films

The electronic structure of as-grown and high temperature (1625 C) annealed chemical vapour deposition boron-doped (1-4 ppm) diamond films has been studied using a scanning photoelectron microscope with lateral resolution in the 1 mum range. The fresh surfaces have been obtained by cleaving free-standing films in situ at a pressure of 7 X 10(-11) Torr. The major part of the contrast in photoelectron images is due to topography effect but grain structure (grain size 10-50 mum) can be also detected. The detailed study of separate grains shows that as-grown films demonstrate significant intensity in the vicinity of the Fermi level with a characteristic band tail which is believed to result from static and dynamic site disorder. In annealed films a sharp drop in Fermi level intensity is observed and samples show charging effects in scanning electron microscope measurements. As-grown films contain different types of defects which appear as electrically active trapping centers and give rise to the increased density of states at the Fermi level. The evolution of the defect structure and possible boron redistribution upon annealing explains the much lower photoemission signal around the Fermi level in heat-treated films.