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

Abstract

This study delves into a profound exploration, using simple yet effective Monte Carlo ray‐tracing simulations, of the influence of the refractive indices of multiple quantum wells (MQWs) and p‐type electron blocking layer (p‐EBL) on the photon propagation and subsequent light extraction behavior in AlGaN‐based ultraviolet‐C (UVC) light‐emitting diodes (LEDs), covering both transverse‐electric (TE) and transverse‐magnetic (TM) polarized light. Remarkably, the refractive index contrasts at the heterointerfaces of p‐EBL/MQWs/n‐AlGaN have a relatively minor impact on the extraction efficiency of TE‐polarized light but exert a significant influence on TM‐polarized light. This discrepancy arises from the substantial effect of total internal reflection at these heterointerfaces on the propagation of photons emitted at large angles. Thus, this observation elucidates the oversight of photon propagation in the conventional design of MQWs and p‐EBL in AlGaN‐based UVA and UVB LEDs, where TE‐polarized emission predominates. Building upon simulation results, a highly effective strategy for extracting TM‐polarized light in AlGaN‐based UVC LEDs is further demonstrated by combining refractive index engineering with inclined sidewalls. The findings suggest refractive index engineering can serve as a novel design parameter for AlGaN‐based UVC LEDs dominated by TM‐polarized emission, expanding the range of techniques available for enhancing device performance.

A scattered volume emitter micropixel architecture for ultra efficient light extraction from DUV LEDs

“…Various works by other authors have considered or proposed epilayer stacks for UVC LEDs with different refractive indices. Many of these studies consider a rather low refractive index of the active region, a low extinction coefficient for "the p-side" or both [46][47][48][49] . To show how the SVEP architecture performs for different active region refractive indices and p-side loss regimes on the performance of the SVEP architecture, the following epilayer stack cases are considered:…”

A scattered volume emitter micropixel architecture for ultraefficient light extraction from DUV LEDs

“…Various works by other authors have considered or proposed epilayer stacks for UVC LEDs with different refractive indices. Many of these studies consider a rather low refractive index of the active region, a low extinction coefficient for "the p-side" or both [40][41][42][43] . To show how the SVEP architecture performs for different active region refractive indices and p-side loss regimes on the performance of the SVEP architecture, the following epilayer stack cases are considered:…”