Bandgap energies of the group III-V quaternary alloy semiconductor, cubic AlxGa1−xNyAs1−y, were calculated by means of
the dielectric method. While only GaN and GaAs are considered to be direct
transition type among the four constituent binary compounds of this quaternary
alloy system, the calculation results show that the bandgap energy range covered
in the direct transition regime of this alloy system was further extended to the
higher energy side of GaN as well as to the lower energy sides of GaAs. The
extension to the higher energy side was attributed to the larger direct bandgap
of AlN. On the other hand, the extension to the lower energy side was caused by
the large bowing in the bandgap energy between group III nitrides and arsenides.
Calculations under lattice matching to Si and GaAs are also presented.