Abstract
In this letter, we describe the design and fabrication of high-power AlGaN-based ultraviolet (UV) flip-chip high-voltage light-emitting diodes (LEDs) operating at 368 nm with an epitaxial indium tin oxide (ITO)/Al reflecting mirror and symmetry electrode layout. Metal-organic chemical vapor deposition (MOCVD) was used to grow an ITO thin film as a transparent electrode on the LED surface. At 365 nm, epitaxial ITO thin films exhibited a transmittance of up to 93.6%. Additionally, the epitaxial ITO/Al reflective mirror has a reflectance of 81.2% at 365-nm. To investigate the electrical characteristics, four types of HV-LED micro-cells were constructed with varying n-type mesa structures and p-type interconnect electrodes. We demonstrated a forward voltage (Vf) of 7.86 V at 350 mA with a 2 × 2 mico-cells high-voltage ultraviolet 368-nm flip-chip LED after optimising electrode structure and device process.
Highlights
AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) have gained increasing attention due to the growing demand for UV curing, solid-state lighting, medical sterilization, laser security, among other applications (Khan et al, 2008)
The main challenge of developing high-efficiency UV LED chip is to realize the reflective electrode with high reflectivity, good contact and stable operation in 365 nm band
Another issue to resolve is the interconnection between the flip-chip high-voltage LED chip and the substrate
Summary
AlGaN-based ultraviolet (UV) LEDs have gained increasing attention due to the growing demand for UV curing, solid-state lighting, medical sterilization, laser security, among other applications (Khan et al, 2008). Dr Chen observed that by enhancing the quality of the crystal material, the ITO material generated by MOCVD process has a 95% transmittance in the ultraviolet 365 nm band (Chen et al, 2017). We applied this material to the LED reflector in this investigation. Another issue to resolve is the interconnection between the flip-chip high-voltage LED chip and the substrate. The manufacturing of UV 368nm AlGaN-based flip-chip high-voltage LEDs in this work utilized an epitaxial indium tin oxide/Al reflecting mirror and symmetry electrode configuration. Various types of HV-LED microcells with an n-type mesa structure and a p-type connecting electrode were developed
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