MOVPE-grown AlGaN-based tunnel heterojunctions enabling fully transparent UVC LEDs

We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characteristics can be improved by exploiting the higher conductivity of n-AlGaN layers as well as a lower resistance of n-contacts. UVC LEDs with AlGaN:Mg/AlGaN:Si tunnel junctions exhibiting single peak emission at268 nm have been realized, demonstrating effective carrier injection into the AlGaN multiple quantum well active region. The incorporation of a low band gap interlayer enables effective tunneling and strong voltage reduction.Therefore, the interlayer thickness is systematically varied. Tunnel heterojunction LEDs with an 8 nm thick GaN interlayer exhibit continuous-wave emission powers >3 m W near thermal rollover. External quantum efficiencies of 1.4% at a DC current of 5 m A and operating voltages of 20 V are measured on-wafer. Laterally homogeneous emission is demonstrated by UV-sensitive electroluminescence microscopy images. The complete UVC LED heterostructure is grown in a single epitaxy process including in situ activation of the magnesium acceptors.

Electrical and optical characteristics of highly transparent MOVPE-grown AlGaN-based tunnel heterojunction LEDs emitting at 232 nm

We present the growth and electro-optical characteristics of highly transparent AlGaN-based tunnel heterojunction light-emitting diodes(LEDs)emitting at 232 nm entirely grown by metalorganic vapor phase epitaxy(MOVPE).A GaN:Si interlayer was embedded into a highly Mg-and Si-doped Al_(0.87)Ga_(0.13)N tunnel junction to enable polarization field enhanced tunneling.The LEDs exhibit an on-wafer integrated emission power of 77μWat 5 mA,which correlates to an external quantum efficiency(EQE)of 0.29%with 45μWemitted through the bottom sapphire substrate and 32μW emitted through the transparent top surface.After depositing a highly reflective aluminum reflector,a maximum emission power of 1.73 mW was achieved at 100 mA under pulsed mode operation with a maximum EQE of 0.35%as collected through the bottom substrate.