Superlattice-wedge electron blocking layer and quantum barrier architecture analysis for high-efficiency algan-based ultraviolet light-emitting diode

Abstract

AlGaN-based ultraviolet Light-Emitting Diode (UV-LED) is an important lighting source in various fields such as the medical sector, water/food treatment industry, sterilization and disinfection devices, agriculture/horticulture and communication. UV-LED offers notable advantages including compact form, long lifespan, and environmentally friendly. Despite this potential, the efficiency of AlGaN-based UV-LED remains significantly lower than that of visible LED, primarily due to poor carrier injections and inadequate carrier confinement in the active region. Insufficient confinement of electrons and holes leads to increased carrier leakage and non-radiative recombination outside the quantum well (QW), especially at high current densities. Consequently, the UV-LED suffers from efficiency droop, referring to a phenomenon where the internal quantum efficiency (IQE) decreases at high current injection. This thesis presents a comprehensive investigation into mitigating efficiency droop of UV-LED through band-engineering, focusing on optimizing quantum barriers (QB) and introducing a superlattice-wedge electron blocking layer (SW-EBL) to enhance the performance of ~270 nm AlGaN-based UV-LED.The simulation is performed by using open-source software, One Dimensional Poisson, Drift-Diffusion, and Schrodinger Solver (1D-DDCC) which is validated with existing literature through IV characteristic and emission wavelength. The analysis covers optoelectronics properties such as energy band diagram, electric field distribution, electron and hole concentrations, and radiative recombination rates. The performance of the UV-LED is evaluated through key performance parameters including IV characteristic, LOP, internal quantum efficiency (IQE) and efficiency droop. The analysis on QBs is conducted by simulating three configurations, which are above-, same- and under-level QB were investigated. It is found that under-level QB significantly alleviates the LOP, luminescence intensity IQE by two-, three- and four-fold while maintaining lowest efficiency droop. The EBL parameterization covers four aspects which are thickness, dopant concentrations, aluminium composition and optimal number of QW. The thickness of the EBL is varied from 10 nm to 60 nm with increment of 10 nm, dopant concentrations from 1 "�" 1016 cm-3 to 1 "�" 1019 cm-3 with increment of 101 cm-3, aluminium composition from 70% to 100% with increment of 10% and number of QW from one to seven with increment of two QWs. It is found that the optimal EBL parameters by considering the LOP, luminescence intensity, IQE and efficiency droop for thickness, dopant concentration, aluminium composition and number of QWs is 10 nm to 20 nm, 1 "�" 1016 cm-3 to 1 "�" 1017 cm-3, 80% to 90% and three QWs. Through the analysis on EBL parameters, a superlattice-wedge EBL is introduced and compared with conventional bulk AlGaN EBL. The results reveal that the LOP improved by ~300% from 30 mW to 130 mW, the luminescence intensity by ~700% from 2.3118 "�" 1020 a. u. to 17.9734 "�" 1020 a. u., and the IQE by 73% from 0.653602 to 0.377295. The efficiency droop, measured at 500 Acm-2, also was significantly reduced from 65% to 12%. This research impacts the potential of superlattice-wedge EBL as an alternative for developing a high-performance AlGaN-based UV-LED, offering significant reduction in efficiency droop and paving the way for more efficient and reliable UV lighting source.