Fabricating Ultralow Dislocation Density Microlight-Emitting Diodes on a Silicon Substrate via an Epitaxial Lateral Overgrowth Method

This SEM image shows a cross-sectionalview of the ELO layeron the silicon template. Optimization of the lateral overgrowth conditionrealized a high aspect ratio of the ELO layer. The ELO layer did notcontact with the surface of the ELO mask owing to the ridge structurein the EGOS substrate. Microlight-emitting diodes were fabricated using an originalsubstrate(ELO GaN on silicon; EGOS). The EGOS substrate was fabricated by growinga GaN layer on a (111)-plane silicon substrate via the epitaxial lateralovergrowth technique. The EGOS substrate has a wide mask that formedan open area. The widths of the ELO mask and open area are 51.5 and3.5 mu m, respectively. Whole micro-LEDs could be formed withinthe wing area by widening its width, which has a low defect density.Because the adjacent ELO layers do not coalesce into each other, gapsare present between the ELO layers. The EGOS substrate exhibits aridge structure that is formed via the dry-etched method, facilitatingthe removal of the chips from the EGOS substrate. The optimizing growthcondition of the ELO GaN layer was realizing 3.2 mu m in thicknesseven though the width of the LEO layer is over 47 mu m. Cathodeluminescence measurement did not show dislocations at the wing areaof the ELO layer. The micro-LEDs fabricated via this method emittedat 424 nm, proving the feasibility of the method. The original substratewith an ELO layer can be used as a platform to fabricate many kindsof microlight sources with an ultralow dislocation density.