Transmission electron microscopy and X-ray diffraction were used to assess the microstructure and strain of AlxGa1–xN (x = 0.61 to 0.64) layers grown on AlN. The compressively-strained AlGaN was partially relaxed by inclined threading dislocations, similar to previous observations on Si-doped AlGaN; however, in this material, the dislocations bent before the introduction of any Si. The bending may be initiated by the greater lattice mismatch or the lower dislocation density of the material, but the presence

of Si was not necessarily required. The relaxation by inclined dislocations was quantitatively accounted for by the Romanov-Speck model, and the predicted linear dependence of relaxation upon layer thickness was demonstrated. Such relaxation was not found in tensile-strained AlGaN, grown on GaN, even though the same mechanism appeared to apply.

Relaxation of Compressively-Strained AlGaN by Inclined Threading Dislocations. D.M.Follstaedt, S.R.Lee, P.P.Provencio, A.A.Allerman, J.A.Floro, M.H.Crawford: Applied Physics Letters, 2005, 87[12], 121112 (3pp)