Japan's National Institute of Advanced Industrial Science and Technology (AIST) developed a deep UV LED with the purpose of diamond semiconductor.

AIST plans to reveal the details at the 56th Spring Meeting, 2009 of the Japan Society of Applied Physics, which will take place from March 30 to April 2, 2009, in Ibaraki Prefecture, Japan.

The deep UV LED is collected of a 2mm-square diamond substrate on which a p-i-n-structured diamond semiconductor is stacked. It emits deep ultraviolet light with an emanation wavelength of 235nm. The output is 30μW when a 320mA current is supplied.

"The LED is very close to practical use," said Satoshi Yamasaki, major research scientist of the Energy Technology Research Institute of AIST and a professor at Graduate School of Pure and Applied Sciences at University of Tsukuba.
According to AIST, the new LED has two most important characteristics. First, its glowing efficiency continues to increase even when a large current is supplied. Second, it has an outstanding resistance to high temperatures.

Specially, when a current with a density exceeding 2,000A/cm2 is applied through an electrode with a diameter of 120μm, the luminous efficiency continues to increase without being saturated, according to AIST. At present, the operating current density of a deep UV LED using AlGaN-based semiconductors, which may equal the new LED, is only 500A/cm2 at a maximum, AIST said.

In view to the excellent heat resistance, even when temperature rises from room temperature to 420°C, the light emission intensity does not degrade but continues to increase, AIST said.

Unlike general LEDs, the diamond LED emits light because of the creation of "excitons." An exciton is an electron-hole pair that behaves like a kind of particle. In general, it is susceptible to heat and often deteriorates quickly.

Though, the excitons generated in the diamond LED are "very stable and will not break until 600°C," said Toshiharu Makino, researcher of the Energy Enabling Technology Group at the Energy Technology Research Institute of AIST. This is the main reason for the excellent high-temperature resistance.