The deep-UV LED developed this time uses a design of stacking a pin-structured diamond semiconductor on a 2 mm square diamond substrate. A deep ultraviolet ray having an emission wavelength of 235 nm is used. The output power when injecting 320mA current is 30Î¼W. â€œIt is close to the practical levelâ€ (School Researcher, Institute of Mathematical and Materials Chemistry, University of Tsukuba).
According to the Research Institute of Production, the LED has two major features: (1) the luminous efficiency continues to increase even when the large current is turned on, and (2) the high temperature resistance. For example, even if a current having a current density of more than 2000 A/cm 2 is turned on by an electrode having a diameter of 120 Î¼m, the luminous efficiency does not reach saturation, but continues to rise. At present, the working current density of deep ultraviolet LEDs using competitive materials AlGaN-based semiconductors is about 500A/cm2.
In terms of high temperature resistance, even if the temperature is raised from room temperature to 420 Â° C, the luminous intensity does not decrease, but continues to increase. Unlike ordinary LEDs, diamond LEDs use the principle of "exciton" as the principle of illumination. Excitons are electrons that move like particles? Hole pairs. However, under normal circumstances it is not heat resistant and most excitons will soon break down. The excitons generated by diamond LEDs are â€œvery stable, even if they are not broken at a temperature of 600 Â°Câ€ (Mr. Makino, a special researcher at the Department of Power and Energy Research, Research Institute of Energy Technology, ITRI). This is the reason for the high temperature resistance.
In the near future, a significant cost reduction will be achieved. Previously, the price of diamond used as a diamond LED backplane was very high, and only a diamond substrate of several mm square was obtained, which could not reach a practical level. In response to this, Makino said: "The technology of laminating polycrystalline diamond semiconductor films on silicon wafers is currently under development. The efficiency is only one digit lower than the LEDs developed this time. Due to the extremely common materials such as silicon and methane, If it is put into practical use, it can manufacture diamond LEDs at very low cost."
The structure of this diamond LED
The temperature dependence of the luminescence spectrum at an injection current of 50 mA. The luminescence intensity continued to increase at 421 Â°C.
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