Improved Reliability of 278 nm Deep Ultraviolet AlGaN-Based Flip-Chip Light Emitting Diodes by Using ITO/Al Contact

We investigated the electrical and optical performance and reliability of 278 nm deep ultraviolet (DUV) AlGaN-based flip-chip light-emitting diodes (FCLEDs) fabricated with ITO/Al and reference Ni/Au contacts. The DUV FCLEDs with the Ni/Au and ITO/Al contacts yielded forward voltages of 6.52 and 6.65 V at 50 A cm −2 and light output of 6.36 and 10.06 mW at 50 A cm −2 , respectively. The ITO/Al-based FCLEDs produced higher Wall plug efficiency (WPE) (3.04% at 50 A cm −2 ) than the Ni/Au-based samples (1.96%). The ITO/Al-based FCLEDs revealed 55% higher WPE at 50 A cm −2 than the Ni/Au-based sample. For both of the samples, the output power decreased with increasing operation time at 100 A cm −2 . For example, after 2000 h, the Ni/Au and ITO/Al-based FCLEDs showed a reduction in the output power by 37% and 22%, respectively. Despite the good output characteristics, the ITO/Al contact-based FCLEDs exhibited higher forward bias voltages than the Ni/Au-based sample. Based on the energy dispersive X-ray spectroscopy (EDS) depth profiles, high-angle annular dark field (HAADF), and electron energy loss spectroscopy (EELS) results, reason for the increase in the forward voltage of ITO/Al-based FCLEDs is described and discussed.