Mosaic structure and its influence on carrier mobility in undoped hexagonal GaN thin film

The different kinds of mosaic structure in a series of hexagonal GaN thin f ilms, prepared by low pressure metal-organic chemical vapor deposition, wer e studied by high resolution X-ray diffraction analysis and transmission el ectron microscopy (TEM). The rocking curves of (0002), (10 (1) over bar 2), and (20 (2) over bar 1) planes were measured, and some calculation was car ried out to distinguish two different mosaic structures: the in-plane twist and the out-of-plane tilt. The different threading dislocations were deduc ed from the corresponding mosaic structures. It is found that the carrier m obility is much more sensitive to the substrate normal tilt than to the in- plane twist of the grain. Dislocations with different Burgers vectors are s uggested to exert different influence on carrier mobility of the GaN film. Most of the dislocations in the him are in-plane twists, with a lesser amou nt of out-of-plane tilts, which strongly influences the mobility. The resul t may help explain the fact that the density of the dislocations in the GaN thin films is very high, but the films still show a high efficiency. (C) 2 000 Elsevier Science S.A. All rights reserved.