Determination of the cubic to hexagonal fraction in GaN nucleation layers using grazing incidence x-ray scattering

Recent electron diffraction and microscopy studies of GaN nucleation layers have shown that, faults in the stacking of the close-packed planes result in the coexistence of cubic and hexagonal phases within the layers. Using grazing incidence x-ray scattering, we have quantified the proportion of the cubic and hexagonal phases throughout the nucleation layer. We compare the structure of a 20 nm nucleation layer grown on sapphire by atmospheric pressure metal-organic chemical vapor deposition at 525 degrees C to that of an identical layer heated to 1060 degrees C. The fractions of cubic and hexagonal phases in the layers are determined by a comparison of the scattering data with a Hendricks-Teller model. High temperature exposure results in a decrease of the cubic fraction from 0.56 to 0.17. The good agreement with. the Hendricks-Teller model indicates that the positions of the stacking faults are uncorrelated, (C) 1998 American Institute of Physics.