Semiconductors based on the family of gallium nitride (GaN) and its alloys with indium nitride (InN) have been extensively used over the past several years for the development of blue-green and white light emitting diodes (LEDs). Such devices have found widespread applications in outdoor and consumer electronic displays and gradually are targeting to replace the incandescent and fluorescence lamps for general illumination. Furthermore, the development of blue-violet lasers has revolutionized the field of optical recording for information storage. On the other hand deep UV emitters (UV-LEDs) based on alloys of GaN and aluminum nitride (AlN) have not yet been developed to the degree required to address the medical and industrial applications discussed previously. Previous work, discussed in References 13 and 14, has shown that these deep UV emitting alloys can be made to have internal quantum efficiency 50% or higher. However, the difficulty in doping these wide band gap semiconductors with n- and p-type impurities prevents the development of efficient deep UV-LEDs in the traditional form of p-n junctions. The authors of this article have addressed this fundamental problem by injecting the electron-hole pairs in the AlGaN alloys by electron beam pumping rather by the traditional p-n junction scheme.
This novel and compact deep UV-emitter consists of a glass vacuum tube, which houses the semiconductor in the form of AlGaN /AlN quantum wells as well as a field emitter made of a grapheme nanoneedle (GN). The use of GN as the field emitter is one of the main innovations in the development of this deep UV emitter. The authors report that such field electron emitter achieves stable and high brightness field emission at a high residual pressure of about 10-4 Pa for more than 5000 hours. This is to be contrasted with thermionic emitters or other types of field emitters such as carbon nanotubes which require a vacuum of less than 10-7 Pa. This property of grapheme is due to its unique quantum structure which leads to high electron mobility. The current required to drive the field emitter is very low (100 µA) and thus the device can be driven by AA dry batteries in series. The device emits at 240 nm with output power of 20 mW and power efficiency of 4%. Thus, this compact and light weight deep UV-emitter is likely to be able to address some of the applications discussed previously.
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