Biaxial strain and lattice constants of InN (0001) films grown by plasma-assisted molecular beam epitaxy

We present a systematic study, using high resolution x-ray diffraction, of the in-plane a and out-of-plane c lattice parameters of high quality InN films grown by molecular beam epitaxy on GaN/Al2O3 (0001) substrates. It is found that their values are dependent on the nucleation and growth conditions. Films nucleated in a two- or three-dimensional growth mode exhibit biaxial compressive or tensile strain, respectively. The linear dependence of c on a is consistent with biaxial strain being present in the films. A biaxial strain relaxation coefficient of 0.43 +/- 0.04 is deduced. The values of the lattice constants for the case of strain-free InN are estimated to be in the ranges c=5.699 +/- 0.004 A and a=3.535 +/- 0.005 A. (c) 2006 American Institute of Physics.