Postdoctoral Researcher, University of California, Santa Barbara
ECE Faculty Candidate Seminar
Monday, February 6, 2023, 9:00-10:00 am
B02 Coordinated Science Laboratory Auditorium
Title: Micro-LEDs with MOCVD-grown tunnel junctions and properties of efficient InGaN red Micro-LEDs
Abstract: Micro-size light-emitting diodes (μLEDs) have attracted huge attentions as the next-generation display technology for the wide applications, such as wearable watches, virtual/augmented reality, micro-projectors, and ultra-large televisions. InGaN LEDs or laser diodes with epitaxial tunnel junctions (TJs) are attractive due to several advantages, such as simple fabrication process, higher efficiency, and lower efficiency droop by improved current spreading, less loss. In the first part, high performance InGaN µLEDs with MOCVD-grown TJs were successfully demonstrated using selective area growth (SAG) and p+GaN/InGaN/n+GaN structure. SAG apertures provide paths for the out diffusion of H+ atoms, which passivated Mg atoms in the p-type GaN during the overgrowth of TJs. The forward voltage (Vf) in the SAG TJ µLEDs is independent on the device sizes, suggesting that the H+ atoms are effectively removed through the holes on top of the p-GaN surface. The Vf @ 20 A/cm2 in the TJ µLEDs utilizing SAG is significantly reduced to 3.24 V. Moreover, the output power of TJ µLEDs with SAG is ~10% higher than the common µLEDs with indium tin oxide (ITO) contact. The InGaN TJs µLEDs show a significant reduction of Vf by ~0.6 V compared to the common n-GaN TJs µLEDs. The external quantum efficiency (EQE) of the packaged TJ µLEDs was improved by 6% compared to the common µLEDs with common ITO contact. These demonstrations solve the key challenges of MOCVD-grown TJs. Then, we present fully MOCVD-grown InGaN cascaded µLEDs with independent junction control. The cascaded µLEDs consisted of a blue emitting diode, a TJ, and a green emitting diode. We can control the injection of carriers into blue, green, and blue/green junctions in the same device independently.
Biography: Panpan Li is a postdoctoral researcher in the materials Department at UCSB. She works on tunnel junction, Micro-LEDs, and UV laser diodes. Her activity involves the MOCVD growth, chip fabrication, and testing of Micro-LEDs.