Improved hole injection and carrier distribution in AlGaN deep-ultraviolet light-emitting diodes with bidirectional-staircase-barrier structure

High-efficiency 278 nm AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) adopting the bidirectional-staircase-barrier (BSB) structure have been investigated. The experimental results show that the maximum external quantum efficiency (EQE) and wall-plug efficiency (WPE) for the proposed BSB structure reach 8.47% and 7.01%, respectively. Furthermore, compared with the reference structure, showing a tremendous improvement of 32% and 31%, respectively. Numerical simulation results show that the BSB structure enhances the electron confinement of the quantum barriers (QBs) as well as improves the hole injection, resulting in a 170% increase in the hole concentration for the active region. Meanwhile, integrating a 2-nm-thick thin-strip-barrier on two QBs close to the p-side can modulate the energy band flatter, which facilitates hole migration and achieves a more uniform distribution of holes in the active region. The more uniform carrier distribution improves the radiative recombination rate of the BSB structure by 147% compared to the reference structure. Furthermore, the dramatic increase of the radiative recombination rate in the three quantum wells (QWs) close to the n-side proves that the BSB structure achieves more QWs to participate in effective radiative recombination, which significantly enhances the quantum efficiency of the DUV-LEDs.