The Need

III-Nitride ultraviolet light emitting diodes (UV LEDs) have a variety of promising applications, including sterilization and water purification. Currently, UV LEDs use an absorbing p-GaN top layer for hole injection, which reduces light extraction efficiency to lower than 20%. UV light emissions down to 210 nm have been achieved for AlGaN-based UV LEDs, but the wall-plug efficiency (WPE) of UV LEDs remains much lower than InGaN-based visible LEDs. The reduced efficiency is attributed to a combination of the poor light extraction efficiency due to high internal light absorption in the widely used p-GaN cap layer and the low injection efficiency associated with the low thermally activated hole density. Thus, there is a need to improve this light extraction efficiency.

The Technology

Researchers at The Ohio State University, led by Dr. Siddharth Rajan, have developed a novel method to enhance light extraction efficiency in tunnel-injected III-Nitride ultraviolet LEDs. This method uses relfective surfaces on top of a tunnel junction based LED structure to enhance both the transverse electric and transverse magnetic polarized light. In this approach, the sidewall of the LED is etched to create facets at an angle to the quantum well plane. Reflective material is deposited on these contacts so that both horizontally and vertically oriented light beams incident on the mirror surface are reflected downward after one or more passes.

Commercial Applications

• LED lights

Benefits/Advantages

• Minimizes internal light absorption
• Greatly enhanced light extraction efficiency; Could lead to up to 80% light extraction efficiency