High-Performance Nitride Vertical Light-Emitting Diodes Based on Cu Electroplating Technical Route

Abstract

GaN-based vertical-geometry light-emitting diodes (V-LEDs) are considered as ideal candidates for future high-power and high-efficiency lighting devices. However, the optoelectrical performance, yield, and stability of V-LEDs are still inferior than the conventional lateral LEDs (L-LEDs) due to some fabrication process hurdles, such as the p-type reflective electrode, nitrogen-polar (N-polar) n-type contact, surface texturization, insufficient current diffusion, and the foreign conductive substrate transfer. Here, we present a minireview of our long-term efforts on V-LEDs fabrication based on Cu electroplating foreign substrate transfer technical route. The electroplating approach shows its inherent advantages of moderation, flexibility, and reliability, yet still hampered by some technical hurdles specifically for V-LEDs fabrication: nonuniformity, easily thermal deformation, difficult to dice out. Since the foreign substrate transfer process is the most critical step, here, first, we introduced our efforts on Cu electroplating manipulation in detail: optimized the polishing and grinding process, Cu:W pseudoalloy and Cu/Ni bilayer electroplating, hybrid wet-etching plus dry laser scribing, and fully wet-etching approaches. Then, we summarized our investigation results for the p-type reflective electrode, nitrogen-polar (N-polar) n-type contact deposition, surface texturization, and current diffusion boost design. Based on the rationally manipulated process, the assembled V-LEDs show excellent optoelectrical performance: record-low forward voltage ( $V_{F}$ , 2.75 V at 350 mA, 3.04 V at 1000 mA, 1 mm2), low reverse leakage current ( $IR$ , 0.1– $0.25~\mu \text{A}$ at −10 V), high lumen efficiency (115 lm/W at 350 mA), low thermal resistance (RT, 1.58 °C/W for V-LEDs chip and 12.06 °C/W for V-LEDs lamp), high yield (>90%), and long-term stability.