Strain and dislocation reduction in maskless pendeo-epitaxy GaN thin films
Measurement of strain in GaN films grown via pendeo-epitaxy (PE) indicates that the overgrowth, or wing, material is crystallographically relaxed. An increase of approximate to0.02% in the c-axis lattice parameter of the wing material was measured via high-resolution X-ray diffraction (HRXRD); additional evidence for this increase was indicated by an upward shift of the E2 Raman line frequency. Atomic force microscopy studies revealed a reduction in the density of mixed-type dislocations in the wing. A reduction in screw-type dislocations in the wings with respect to the stripes is indicated by a reduction in HRXRD rocking curve FWHM of the (0002) reflections from 646 to 354 arcsec. The off-axis FWHM of the wing area was 126 arcsec compared to 296 arcsec for the stripe indicating a reduction in the edge-type dislocations as well. Pendeo-epitaxy growth of wings off the (1120) surface of a GaN stripe produced a material that is crystallographically relaxed, contains fewer defects compared to the stripe and is atomically smooth on the (1120) surface.