Thermally stable indium contact to N-polar n-GaN for reliable vertical light emitting diodes

Thermally stable indium (In) contact formed on N-polar n-GaN was investigated for the fabrication of reliable vertical GaN-based light-emitting diodes (LEDs). The electrical properties and Ohmic mechanism of an In contact to N-polar n-GaN were investigated using transmission line model methods, atomic force microscopy, secondary electron microscopy (SEM) after focused ion beam (FIB) milling, and secondary ion mass spectroscopy (SIMS). Specifically, the In contact formed on the wet-etched N-polar n-GaN, which consisted of {10-1-1} crystallographic semipolar planes, showed near Ohmic behavior under the as-deposited condition. Notably, the thermal annealing performed at 250 ° C for 1 min in N₂ ambient led to a significant improvement in the contact properties, e.g., the specific contact resistance was 7.2 x 10^-2 and 4.7 x 10^-3 Ωcm² for the as-deposited and annealed condition, respectively. Interestingly, the interfacial reaction between In and GaN observed by SIMS was insignificant. Alternatively, the SEM observation of the In/GaN interface after FIB milling showed that the thermal annealing removed the interfacial voids and improved the adhesion between In and GaN, which is thought to cause improved Ohmic contact. Considering the positive annealing dependence of the In contact to N-polar American n-GaN, In metal is proposed Publishers for the fabrication of reliable vertical LEDs.