Comparison of nitrogen compositions in the as-grown GaN_xAs _1-x on GaAs measured by high-resolution x-ray diffraction and secondary-ion mass spectroscopy

High-resolution x-ray diffraction (HRXRD) and secondary-ion mass spectroscopy were used to measure the N compositions of a series of as-grown GaNAs samples grown by solid-source molecular-beam epitaxy. We found that N compositions measured by the two methods agree well at lower N compositions (x<3%), and deviate at larger N compositions (x>3%). The HRXRD measurement by using Vegard's law to extract the lattice constant of GaNAs, underestimates N composition at larger N compositions. We found that the underestimation is up to 14.3% at the x=4.2%. In order to explain the deviation, a model for analyzing the correlation between lattice parameters and point defects in the epilayer was carried out.