Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers

Abstract

To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.

A Review of Recent Research Advances on AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

“…In order to overcome the problems caused by the polarization effect, Jain et al [82] investigated the quantum barrier structure of MQWs and proposed the use of a gradual step quantum barrier (GSQB) instead of the conventional quantum barrier in the structure of EBLs-free AlGaN-based DUV-LEDs, as shown in Figure 24. The use of this structure effectively reduces the QCSE of the MQWs and improves the overlap of the electron and hole wave functions.…”

Refractive Index Engineering as a New Degree of Freedom for Designing High‐Performance AlGaN‐Based Ultraviolet C Light‐Emitting Diodes

“…[29] In addition to extensive research on p-EBL, some studies have explored modifications to the MQWs to enhance electron confinement, such as gradually increased barrier thicknesses, [30] composition-graded quantum barriers (QBs), [31] delta-accelerating QBs, [32] and Mg delta-doped last quantum barrier (LQB). [33] Conversely, to mitigate the detrimental effect of the EBL on hole injection, EBL-free LED designs have been proposed by engineering the MQWs to self-suppress electron overflow, including graded staircase QBs, [34] linear graded QBs, [35] multiple-symmetrical-stair QBs, [36] and graded Al-content AlGaN insertion layer. [37] Previous studies on the design of MQWs and EBL have primarily focused on improving carrier injection or confinement to enhance IQE.…”

285 nm AlGaN-BASED DEEP-ULTRAVIOLET LED WITH HIGH INTERNAL QUANTUM EFFICIENCY: COMPUTATIONAL DESIGN

“…One of the most recent studies performed by Hirayama et al have introduced an AlGaN UV-C LED with high power in which a photonic crystal reflector was used [28]. Jain et al proposed graded staircase quantum barriers against electron leakage problem for AlGaN DUV LEDs [29]. A high LEE was measured by Zhang et al for Ag-nanodots and Al electrodes adoption on AlGaN LED operating at ~280 nm [30].…”