Recent progress of research on III-nitride deep ultraviolet light-emitting diode

Abstract

III-nitride based ultraviolet light-emitting diodes (UV LEDs) have recently attracted more and more attention for their great potential in a wide range of applications, such as water and air purification, disinfection, polymer curing, biochemical detection, non-line-of-sight communications and special lighting. The bandgaps of GaN, AlN and InN are 3.43, 6.04 and 0.65 eV, respectively, which make them the ideal materials for developing efficient UV light-emitting devices. In the past decade, great progress has been achieved on III-nitride based UV LEDs. UV LED devices with emitting wavelength from 400 nm to 210 nm have been developed successively. For deep UV LEDs (DUV LEDs) of emitting wavelength shorter than 360 nm, the highest value of external quantum efficiency has exceeded 10%. To a large extent, these achievements most benefited from the development of the key AlGaN material epitaxial techniques. For UV LEDs operating at relatively shorter wavelengths, alloy compositions with greater aluminum content are required. However, as the aluminum content increases, it has become more and more challenging to obtain high quality epitaxial material as well as efficient doping (especially for p-type doping), which is resulted from the intrinsic properties of Al(Ga)N material and adds a degree of complexity to the development of efficient UV light-emitting devices. In this paper, we reviewed the key difficulties as well as the important research progress in the research and development of III-nitride DUV LED, involving the epitaxial and doping issues of Al(Ga)N film material, AlGaN based quantum confining structure and its internal quantum efficiency, the key processing techniques of device fabrication, various methods to enhance light extraction efficiency, the thermal management and reliability of UV LEDs. Performances of state-of-the-art UV LEDs as well as promising future solutions are also discussed in the paper.