The growth and properties of mixed group V nitrides

Bearing in mind the problems of finding a lattice-matched substrate for the growth of binary group III nitride films and the detrimental effect of the large activation energy associated with acceptors in GaN, we propose the study of the alloy system AlGaAsN. We predict that it may be possible to obtain a direct gap alloy, with a band gap as wide as 2.8eV, which is lattice-matched to silicon substrates. The paper reports our attempts to grow GaAsN alloy films by molecular beam epitaxy on either GaAs or GaP substrates, using a radio frequency plasma source to supply active nitrogen. Auger electron spectra demonstrate that it is possible to incorporate several tens of percent of nitrogen into GaAs films, though x-ray diffraction measurements show that such films contain mixed binary phases rather than true alloys. An interesting observation concerns the fact that it is possible to control the crystal structure of GaN films by the application of an As flux during growth. In films grown at 620°C a high As flux tends to increase the proportion of cubic GaN while also resulting in the incorporation of GaAs. Films grown at 700°C show no evidence for GaAs incorporation; at this temperature, it is possible to grow either purely cubic or purely hexagonal GaN depending on the presence or absence of the As beam.