Bandgap energy of GaNAs alloys grown on (001) GaAs by metalorganic molecular beam epitaxy

GaNAs layers have been successfully grown on GaAs(001) substrates by metalorganic molecular beam epitaxy using monomethylhydrazine (MMHy) as a N source. The N composition in GaNAs increased with decreasing growth temperature and with the increasing MMHy precursor ratio in the group-V precursors. We obtained a N composition of 7.2% in GaNAs. With the increased N composition, the absorption spectra shifted to lower energy and the absorption coefficient increased by one order of magnitude. When the N composition in GaNAs is less than 1%, the measured bandgap energy is very close to the theoretical bandgap energy based on the dielectric model. However, for N composition larger than 1%, the bandgap energy deviated considerably from the dielectric model, and approached the theoretical bandgap energy based on the first-principles supercell models.