Growth modes and coupled morphological-compositional modulations in GaP1-xNx layers grown on nominally (001)-oriented Si substrates

We investigated the chemical beam epitaxy of GaP1-xNx to correlate the growth parameters with their properties when they are grown on nominally (001)-oriented Si substrates, as desired for the lattice-matched integration of optoelectronic devices with the standard Si technology. The growth mode as well as the chemical, morphological and structural properties of samples prepared using different growth temperatures and N precursor fluxes were analyzed by RHEED, XRD, RBS, NRA, EDX spectroscopy, AFM and TEM. Our results show that, up to x = 0.04, it is possible to synthesize smooth and chemically homogeneous GaP1-xNx layers with a high-structural quality in a 2D fashion, namely, layer-by-layer. For a given N mole fraction, the layer-by-layer growth mode is favored by lowering the growth temperature while decreasing the N precursor flux. As the flux of the N precursor is increased at a given temperature to enhance N incorporation, the quality of the layers degrades upon exceeding a temperature-dependent threshold; above this threshold, the growing layer experiences a growth mode transition from 2D to 3D after reaching a critical thickness of a few nm. Following that transition, the morphology and the chemical composition become modulated along the [110] direction with a period of several tens of nm. The surface morphology is then characterized by the formation of {113}-faceted wires, while the N concentration is enhanced at the troughs formed in between adjacent (113) and (-1-13) facets. We conclude on the feasibility of fabricating homogeneous thick GaP1-xNx layers lattice matched to Si (x = 0.021) or even with N content up to x=0.04. The possibility of exceeding a N mole fraction of 0.04 without inducing coupled morphological-compositional modulations has also been demonstrated when the layer thickness is kept below the critical value for the 2D-3D growth mode transition.