Enhanced p-type Ohmic contact performance in FCLEDs by manipulating thermal stress distribution to suppress Ag agglomeration

Abstract

The implementation of reflective p-type Ohmic contact is an effective way to solve current crowding and improve the optoelectronic performance of flip-chip light-emitting diodes (FCLEDs). Here, we investigate the effects of annealing temperature, annealing time, and N2 flow rate on the formation for Ag/p-GaN Ohmic contact and determine the optimal annealing process parameters. After inserting an indium-tin oxide layer between Ag and p-GaN, the specific contact resistance decreases from 6.66 × 10−3 to 1.86 × 10−3 Ω cm2. In addition, we discover the appearance of a “black line” around the edges of the chips after high-temperature annealing. Finite element analysis and experiments show that the “black line” is related to Ag agglomeration under high temperatures due to stress concentration at the edges of the chips. A strategy for manipulating the stress concentration by adjusting the thickness of the TiW diffusion barrier layer is proposed based on insight obtained by modeling the stress distribution at the edge of the chips. The electrical properties of the fabricated FCLEDs show that the proposed stress manipulation strategy solves the problem of “black line” effectively and maintains the performance of the chips well.