The threading dislocation structure and density was studied in In- and N-face InN films grown on GaN by plasma-assisted molecular beam epitaxy. The threading dislocation densities were determined by non-destructive X-ray diffraction rocking curve measurements in on-axis symmetric and off-axis skew symmetric geometries and calibrated by transmission electron microscopy measurements. Threading dislocation densities were dominated by edge-type threading dislocations with screw-component threading dislocations accounting for less than 10% of the total threading dislocation density. A significant decrease in edge-type threading dislocation density was observed for In-face InN films grown at increasingly higher substrate temperatures. In-face InN films grown with excess In exhibited lower threading dislocation densities compared to films grown under N-rich conditions. The edge-type threading dislocation density of N-face InN films was independent of substrate temperature due to the higher allowable growth temperatures for N-face InN compared to In-face InN. Threading dislocation densities in In-face InN also showed a strong dependence on film thickness. Films grown at a thickness of less than 1μm had higher threading dislocation densities compared with films grown thicker than 1μm. The lowest measured threading dislocation density for an In-face InN film was ∼1.5 x 1010/cm2 for 1μm-thick films.

Evaluation of Threading Dislocation Densities in In- and N-Face InN. C.S.Gallinat, G.Koblmüller, F.Wu, J.S.Speck: Journal of Applied Physics, 2010, 107[5], 053517