Optimization of p-Bonding Electrodes on ZnO:Ga in GaN-Based Light-Emitting Diodes

We propose the optimal p-bonding electrode (p-BE) schemes on single-crystalline Ga-doped ZnO (ZnO:Ga) in GaN-based light-emitting diodes (LEDs) by means of Cr (3 nm)/Al
_0.9
Cu
_0.1
(50 nm) reflection-assisted layer (RAL) and Pd
_0.8
Al
_0.2
/Ni/Au layers. Design factors for the p-BE were described from standpoints of bond strength, electrically equivalent circuit, and photon reflection. From contact test results, the Cr/Al-Cu RAL/Pd-Al/Ni/Au scheme is much more attractive than other schemes, indicating the optimal scheme for ZnO transparent-conducting electrode (TCE). The comparisons from device-performance characteristics showed that the forward voltage and output power of the LED having Cr/Al-Cu/Pd-Al/Ni/Au in the open-structured ZnO:Ga are significantly improved, as compared to those of LEDs with conventionally used Cr/Al/Ni/Au in the open-structured indium tin oxide and ZnO:Ga. In addition, for acceleration test under high-stress current density of 99 A/cm
²
, a degradation rate of the proposed bonding electrode-applied LED is ~190 times as low as that of the other LEDs, indicating longer lifetime and much more thermal stability. Based on the test results, the suggested p-BE is quite attractive for achieving high-performance and excellent reliability GaN-based LEDs with a single-crystalline ZnO TCE.