Photoluminescence of heterostructures with GaP$_{1-x}$N$_x$ and GaP$_{1-x-y}$N$_x$As$_y$ layers grown on GaP and Si substrates by molecular-beam epitaxy

The structural and optical properties of heterostructures containing GaP$_{1-x}$N$_x$ ternary and GaP$_{1-x-y}$N$_x$As$_y$ quaternary alloy layers are discussed. The heterostructures are grown by molecular-beam epitaxy on GaP and Si substrates. The structures are studied by the high-resolution X-ray diffraction technique and photoluminescence measurements in a wide temperature range from 10 to 300 K. In the low-temperature photoluminescence spectra of the alloys with a low nitrogen fraction ($x<$ 0.007), two clearly resolved narrow lines attributed to the localized states of nitrogen pairs and the phonon replicas of these lines are observed.