Heavy Mg Doping to Form Reliable Rh Reflective Ohmic Contact for 278 nm Deep Ultraviolet AlGaN-Based Light-Emitting Diodes

Abstract

We investigated the electrical property of reflective non-alloyed Rh contacts to p- Al 0.45 Ga 0.55 N contact layers and the performance of 278 nm flip-chip (FC) LEDs with the Rh and Ni/Au contacts as a function of Mg concentration. The three contact layers contained Mg concentration of 5.7 × 10 19 cm −3 (sample A), 1.0 × 10 20 cm −3 (sample B), and 1.4 × 10 20 cm −3 (sample C). The Rh contacts to the sample A showed non-ohmic behaviour, while the samples B and C were ohmic with contact resistivity of 3.2 × 10 −1 and 3.4 × 10 −2 Ωcm 2 , respectively. The FC-LEDs with the sample A, B, and C with the Rh contacts yielded forward voltages of 7.26, 6.24, and 6.30 V, and output power of 10.46, 10.85, and 10.44 mW at 50 A cm −2 , respectively, whereas that with the sample C (Ni/Au contact) gave 6.51 V and 6.26 mW. The FC-LEDs with p -Al 0.55 Ga 0.45 N (sample D) and p -Al 0.61 Ga 0.39 N (sample E) contact layers (with Mg dopant of 8.0 × 10 19 cm −3 ) displayed forward voltage of 7.41 and 8.72 V at 50 A cm −2 and output power of 11.88 and 15.25 mW, respectively. The Wall-plug efficiency of the sample C, D, and E was estimated to be 3.31, 3.21, and 3.50%, respectively. These results show FC-LEDs fabricated with highly Mg-doped p -AlGaN and Rh contact demonstrate reliable performance upon operating at 100 A cm −2 .