Demonstration of grain reorientation during GaN early stage coalescence grown by novel pendeo-epitaxy approach

In this work, we demonstrate that initially misoriented gallium nitride (GaN) crystalline grains grown on top of GaN/AlN/Si/SiO2 nano-pillars, and which have nucleated independently, realign themselves upon coalescence to form high crystalline quality GaN platelets. Electron backscatter diffraction (EBSD) combined with cathodoluminescence (CL) and scanning x-ray diffraction microscopy (SXDM) provided complementary information on the structural properties of GaN before and during the initial coalescence growth phase. SXDM measurements on GaN coalescing at an early growth stage and on GaN pillars only (prior to growth) confirmed that the initially misoriented GaN pillars coalesce into larger well-defined GaN domains (3.9 μm) very well oriented by themselves, with a spatially varying broadening of the diffraction peak that is maximum at the boundaries between neighboring domains, as identified in the spatially resolved orientation maps. The presence of geometrically necessary dislocations (GNDs) at the domain boundaries detected in the EBSD is confirmed by CL images and the estimated GND density is 2 × 1011 cm−2 in these specific zones. Additionally, statistical analysis of SXDM maps indicated that 0.1° of tilt between neighboring pillars constitutes the limit for the current pendeo-epitaxy growth approach for the formation of pillar groups similar in size to the perfectly aligned GaN domains upon coalescence. This work illustrates the potential of this growth strategy to produce high crystalline quality GaN platelets adapted for micro-LEDs growth, and, most importantly, it provides a microscopic insight into the coalescence process, which could be extended to other materials and growth approaches.