Efficiency improvement analysis of nano-patterned sapphire substrates and semi-transparent superlattice contact layer in UVC light-emitting diodes
Journal
Applied Physics Letters
Journal Volume
117
Journal Issue
26
Date Issued
2020
Author(s)
Abstract
UVC light-emitting diodes (LEDs, λ = 275 nm) with different types of contact layers and sapphire substrates were demonstrated on high-quality AlN templates. For LEDs on flat sapphire substrates (FSSs), replacing the absorbing p-GaN contact with p-AlGaN short-period superlattices (p-SPSLs) strongly enhanced the emission along the substrate normal. The integrated external quantum efficiency (EQE) increased from 2.4% to 3.9% under I = 350 mA. For LEDs with a p-SPSL contact, replacing the FSS with nano-patterned sapphire substrates slightly deteriorated the quality of epitaxy, but the overall EQE is still enhanced to 4.4% under I > 350 mA without lens encapsulation. According to the far-field intensity measurement, the light extraction is better improved along the high emission angle to the substrate normal. The interplay among substrates, dipole polarization, and EQE enhancement factors was further analyzed and discussed in the context. ? 2020 Author(s).
Subjects
Aluminum gallium nitride; Aluminum nitride; Efficiency; Gallium nitride; III-V semiconductors; Sapphire; Substrates; Dipole polarization; Efficiency improvement; Enhancement factor; External quantum efficiency; Far-field intensity measurements; Patterned sapphire substrate; Sapphire substrates; Short period superlattice; Light emitting diodes
Type
journal article