Tunnel-injected sub-260 nm ultraviolet light emitting diodes

TL;DR

This paper demonstrates a novel tunnel-injected deep ultraviolet LED with improved contact resistance and reduced operation voltage, enabling efficient hole injection and high-power deep-UV emission.

Contribution

It introduces a polarization-engineered tunnel junction structure with a graded top contact layer for non-alloyed metal contact, advancing deep UV LED technology.

Findings

Achieved low contact resistance of 4.8x10^-5 Ohm cm^2

Reduced forward voltage from 30.9 V to 19.2 V at 1 kA/cm^2

Confirmed hole injection via 257 nm light emission

Abstract

We report on tunnel-injected deep ultraviolet light emitting diodes (UV LEDs) configured with a polarization engineered Al0.75Ga0.25N/ In0.2Ga0.8N tunnel junction structure. Tunnel-injected UV LED structure enables n-type contacts for both bottom and top contact layers. However, achieving Ohmic contact to wide bandgap n-AlGaN layers is challenging and typically requires high temperature contact metal annealing. In this work, we adopted a compositionally graded top contact layer for non-alloyed metal contact, and obtained a low contact resistance of Rc=4.8x10-5 Ohm cm2 on n-Al0.75Ga0.25N. We also observed a significant reduction in the forward operation voltage from 30.9 V to 19.2 V at 1 kA/cm2 by increasing the Mg doping concentration from 6.2x1018 cm-3 to 1.5x1019 cm-3. Non-equilibrium hole injection into wide bandgap Al0.75Ga0.25N with Eg>5.2 eV was confirmed by light emission at 257 nm. This work demonstrates the feasibility of tunneling hole injection into deep UV LEDs, and provides a novel structural design towards high power deep-UV emitters.