Light emitting diodes (LEDs) emitting ultra-violet (UV) luminescence are highly valuable for applications such as UV lasers, UV fluorescence lighting and high-density data storage. However, some high-power applications of UV LEDs are widely known to suffer from thermal management problems. The light emission intensity of most LEDs also gets degraded at high operating temperatures. These challenges have been a major limiting factor in exploiting such LEDs for high-power, high-intensity applications.
Researchers from the National Institute of Advanced Industrial Science and Technology (AIST) in Japan have, however, recently developed a deep UV LED that addresses the above challenges and is capable of operating at high temperatures and at very high current densities while delivering high performance. Specifically, the light emission intensity of the novel LED continues to increase even at operating temperatures as high as 420°C. Its luminous efficiency also continues to increase without reaching saturation, even while operating at current densities as high as 2000 A/cm². This novel LED, based on a diamond semiconductor, is in clear contrast with a deep UV LED using an aluminium gallium nitride (AlGaN) semiconductor, whose operating current density is only 500 A/cm² maximum.
The researchers designed the UV LED based on a 2 mm² diamond substrate, over which a diamond semiconductor with a p-i-n structure is stacked. The LED emits a deep UV light of wavelength 235 nm, with an output of 30 microwatts when supplied with a current of 320 mA. Unlike typical LEDs, the diamond LED emits light due to the generation of excitons that are very stable and do not break down below 600°C. It is this particular characteristic that gives the novel LED excellent high-temperature resistance.
This novel UV LED could be very valuable for any application requiring operations with high current densities and consequently high temperatures. However, the commercialisation of these LEDs is hindered by the high cost of diamond used for the substrate. The researchers plan to address this challenge next by developing a technique that would enable practical diamond LEDs to be produced at a very low cost. Specifically, this technique would be used to stack a polycrystalline diamond semiconductor film on a silicon wafer, and the resulting prototype would have an efficiency that is only an order of magnitude lower than the current version. Once the problem of cost-effectiveness is addressed, mass production and commercialisation of diamond LEDs for high-intensity applications could be easily achieved.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, patrick.cairns@frost.com, www.frost.com
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