Realization of Electrically Driven AlGaN-Delta-GaN QW DUV Micro-LEDs at 265 nm

Abstract

Quantum efficiency of deep-ultraviolet (DUV) light-emitting diodes (LEDs) is a roadblock for these devices to reach efficiencies comparable to their visible light counterparts. The main contributing factor limiting the internal quantum efficiency (IQE) are the effects of the quantum confined Stark effect (QCSE) and valance subband crossover, which can be mitigated through engineering of the quantum well (QW) active region. This work represents the first fabrication and testing of novel full structure electrically driven AlGaN-delta-GaN QW DUV micro-LEDs ($\mu$LEDs) with mesa dimensions between 10 $\mu$m and 30 $\mu$m. Electrical testing revealed a turn on voltage of approximately 5–6 V, with series resistance dominated post-threshold characteristics. Emission peaks for 10 $\mu$m × 10 $\mu$m and 30 $\mu$m × 30 $\mu$m $\mu$LEDs were located at 262 nm and 264.5 nm respectively, with emission linewidths of 7.1 nm and 13.6 nm. Power measurements showed light output power densities increasing from 50 mW/cm$^{2}$ at 100 A/cm$^{2}$ to nearly 400 mW/cm$^{2}$ at 800 A/cm$^{2}$. Efficiency droop onset occurred at 83 A/cm$^{2}$ for 30 $\mu$m × 30 $\mu$m devices and at 200 A/cm$^{2}$ for 10 $\mu$m × 10 $\mu$m devices. The collective results demonstrate that the AlGaN-delta-GaN QW active region can improve both the IQE and light extraction efficiency of DUV emitting LEDs and could prove to be a viable alternative to conventional designs.