Strain, wing tilt and photoluminescence in epitaxial lateral overgrown GaN on SiC substrates

We investigate the epitaxial lateral overgrowth (ELOG) process on silicon carbide (SiC) to obtain defect reduced gallium nitride (GaN). The large wing tilt of about 4 degrees causes bunches of edge dislocations above the edge of the ELOG mask. The PL signal of these regions is diminished and broadened and a defect correlated emission line at about 3.4 eV is detected here exclusively. The GaN above the edge shows higher tensile stress than both the wing and the window regions. In order to reduce the wing tilt and to avoid its detrimental properties, the material of the ELOG mask was changed from SiO2 to SiNx. With the SiNx mask we were able to reduce the wing tilt by an order of magnitude to values far below 1 degree. The PL signal of the interface regions shows no sign of low quality material above the mask edge