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

Abstract

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.

High Thermal Performance Ultraviolet (368 nm) AlGaN-Based Flip-Chip LEDs with an Optimized Structure

“…In improving the output power of the LED chip, it is essential that the thermal properties are enhanced to deliver optimum performance. The flip-chip LED structure was proposed to address issues associated with optical output power and thermal performance [16][17][18][19]. The light associated with the flip-chip LED is extracted from the transparent sapphire side, without an electrode barrier, and the total reflection is reduced due to the refractive index of sapphire, resulting in greater light efficiency.…”