Nitride layers were grown, using plasma-assisted molecular-beam epitaxy, onto (00•1)-oriented sapphire substrates. This involved electron cyclotron resonance or a radio-frequency plasma source. The substrate bias was varied from -200 to 250V, and resulted in a change in the density and energy of N ions which impinged on the growth surface. The layers were investigated by means of high-resolution X-ray diffractometry and high-resolution transmission electron microscopy. The application of a negative bias during growth had a markedly detrimental effect upon the crystal perfection of the layers which were grown using an electron cyclotron resonance plasma source. This was reflected by a change in the shape and width of (00•2) and (20•5) reciprocal lattice points, as monitored by using triple-axis X-ray measurements. High-resolution transmission electron microscopic images revealed isolated basal-plane stacking faults which probably resulted from the precipitation of interstitial atoms. The crystal damage in layers which were grown using a highly negative substrate bias was comparable to that observed after ion implantation at orders-of-magnitude higher ion energies. This was attributed to the impact of ions on the growing surface. None of these phenomena were observed in samples that were grown using a radio-frequency plasma source.

Ion-induced crystal damage during plasma-assisted MBE growth of GaN layers V.Kirchner, H.Heinke, U.Birkle, S.Einfeldt, D.Hommel, H.Selke, P.L.Ryder: Physical Review B, 1998, 58[23], 15749-55