  GaAsPN layers with a thickness of 30nm were grown on GaP substrates with
metalorganic vapor phase epitaxy to study the feasibility of a single X-ray
diffraction (XRD) measurement for full composition determination of quaternary
layer material. The method is based on the peak intensity of a quasi-forbidden
(002) reflection which is shown to vary with changing arsenic content for
GaAsPN. The method works for thin films with a wide range of arsenic contents
and shows a clear variation in the reflection intensity as a function of
changing layer composition. The obtained thicknesses and compositions of the
grown layers are compared with accurate reference values obtained by Rutherford
backscattering spectroscopy combined with nuclear reaction analysis
measurements. Based on the comparison, the error in the XRD defined material
composition becomes larger with increasing nitrogen content and layer
thickness. This suggests that the dominating error source is the deteriorated
crystal quality due to the nonsubstitutional incorporation of nitrogen into the
crystal lattice and strain relaxation. The results reveal that the method
overestimates the arsenic and nitrogen content within error margins of about
0.12 and about 0.025, respectively.
