High performance and high yield sub-240 nm AlN:GaN short period superlattice LEDs grown by MBE on 6 in. sapphire substrates

Abstract

We develop ultraviolet (UV) light emitting diodes (LEDs) that operate in the sub-240 nm (far UVC) regime. The traditional limitations of high Al content AlGaN—the low light extraction efficiency due to transverse magnetic polarization and the poor doping efficiency—were overcome by using AlN:GaN short period superlattices (SPSLs) of varying compositions throughout almost the entire device structure. The quality of our molecular beam epitaxy process for growing SPSL devices was verified via transmission electron microscopy and x-ray diffraction—together, these demonstrate our capacity for growing high quality interfaces with a great deal of control over the thicknesses of each individual layer. Resistivity measurements of our SPSL were three times smaller than bulk AlGaN of similar composition due to the improved doping efficiency. Devices fabricated on 6 in. sapphire substrates showed uniform performance, leading to over 10 000 functional devices per wafer. Packaged diodes exhibited a peak wall plug efficiency of 0.55% and an output power of 1.7 mW when operated at peak efficiency. The devices had an operating life (70% initial power) of 2800 h (at 20 mA continuous wave). Additionally, they could be driven as high as 1 A, which resulted in a record for radiant flux of a far UVC LED grown on sapphire (17.4 mW).