This Small Business Innovation Research Phase II project will develop and commercialize next-generation high-power deep ultraviolet light emitting diodes (DUV LEDs) with high quality p-type doped AlInGaN layers via migration-enhanced metal-organic chemical vapor deposition (MEMOCVD). DUV LEDs operating in the spectral region from 240 nm to 365 nm are of great importance for medical, bio-analytical, sensing, and homeland security technologies. This project aims to improve the LED efficiency and lifetime by improvements in the material quality, doping, and device design. These enhancements will lay the groundwork for large-scale penetration of high volume markets, such as global sanitation and disinfection. This Phase II project will achieve efficient multiple pass extraction in transparent epitaxial structures through use of high-quality MEMOCVD doped p-AlInGaN top contact layers. Achieving an improved quality of highly doped p-AlInGaN layers will allow creation of a low-cost, high power semiconductor DUV radiation source with wall plug efficiency exceeding 5% and operation lifetimes longer than 5,000 hours.
The broader impact/commercial potential of this project will originate from the market penetration of DUV LEDs into existing markets that require compact and environmentally friendly UV radiation sources. This project will also allow penetration into new applications that were previously unattainable due to the inherent limitations of existing UV lamps or lasers. The primary markets for these devices include bio-medical and analytical instrumentation, fluorescence sensing, ink curing, phototherapy and water/air disinfection. This new technology for manufacturing high-efficiency and long-lifetime DUV devices will allow these semiconductor light sources to have a price point which is competitive with the mature UV lamp technology. This will allow the increased use of an environmentally friendly, mercury-free UV technology for a variety of applications, which will result in a reduction of toxic waste and in the costs associated with mercury lamp disposal. The purification, sterilization, and early warning applications enabled by these new DUV LED sources will also result in an improved quality of life, particularly in the developing world.
Ultraviolet (UV) light emitting diode (LED) are of significant economic and societal importance, but require very novel semiconductor manufacturing processes that currently result in low conversion efficiency from electricity to UV light. This NSF Phase II/IIB project developed novel transparent deep UV LED structures based on patented p-AlGaN short-period superlattices (SPSL) with target valence band discontinuity optimized for high vertical conductivity. Unlike visible LEDs that are based on mature InGaN materials technology, UV LEDs are based on AlGaN materials. Prior to this project, p-type GaN layers have been used for p-contact formation in UV LED devices owing to difficulty of p-type doping of AlGaN with high Al content insufficient for the successful contact formation. Use of p-GaN results in significant losses of the light generated in the quantum wells for devices with the emission peak below 365 nm. Strong absorption in the p-GaN layer also creates additional heat that causes the contact to degrade, leading to premature aging of the device. By using a p-type AlGaN SPSL layer, which is transparent in the UV range of the LEDs, together with a reflective p-contact metal, light heading from the quantum wells to the p-contact is recaptured and reflected out of the LED structure. This not only increases efficiency, but also improves the robustness of the p-AlGaN contact layer, leading to higher performance and lower cost of ownership. Specific design of the SPSL LED light sources represent important technological development for low energy, sustainable, "green" lighting. Similarly, like their white LED counterparts, UV LEDs offer low cost solutions and enable new applications in various market sectors. Low cost UV LEDs with improved efficiency and high power solid state light sources developed during this project are being commercialized to address medical instrumentation, food preservation and storage and ink and polymer curing markets.
