Effect of HfO2 Passivation Layer on Light Extraction Efficiency of AlInN Nanowire Ultraviolet Light-Emitting Diodes

Abstract

Diverse applications of ultraviolet (UV) light in the field of purification, sterilization, detection, surface disinfection, sensing, and many others have been studied mostly on AlGaN light-emitting-diodes (LEDs). However, the external quantum efficiency (EQE) of AlGaN deep UV LEDs is limited due to strong induced polarization fields, high dislocation density, severe electron leakage, difficulty in p-type doping, low internal quantum efficiency (IQE), IQE droop, and low light extraction efficiency (LEE). Alternatively, AlInN semiconductor has been recently gained tremendous attention for high power UV LEDs [1-3]. Our group has successfully demonstrated the first AlInN core-shell nanowire UV LEDs with a relatively high IQE of ~52%[1]. However, the light extraction study of such nanowire LEDs is unexplored. In this context, we have studied the LEE of a single AlInN nanowire UV LED at 220 nm - 400 nm wavelength regime. Moreover, we report that the LEE of a single AlInN nanowire UV LED could be increased by ~60% using HfO2 passivation compared to conventional nanowire LED at 282 nm.The schematic structure of AlInN nanowire UV LED is shown in Figure 1(a). The nanowire is composed of 200 nm n-GaN, 100 nm n-AlxIn1-xN quantum barrier (QB)/40 nm i-AlyIn1-yN quantum well (QW)/100 nm p-AlxIn1-xN QB, and 20 nm p-GaN layer. We have estimated the LEE of nanowire LEDs using the finite difference time domain (FDTD) simulation method. Silicon (Si) is used as a substrate, and the n-GaN layer is tapered with a diameter from 70 nm (bottom) to 100 nm (top). The diameter is set to be 100 nm for the rest of the regions. We have placed a single TM-polarized dipole source at the QW center to calculate LEE for a nanowire LED in the simulations. The estimated LEE of 282 nm wavelength single nanowire AlInN UV LED with various HfO2 passivation layers thickness is provided in Figure 1(b). The LEE of such LED without any passivation is ~25.2%, whereas the maximum recorded LEE is ~40.6% with the utilization of 35nm thickness HfO2 passivation layer. This study provides a promising approach for enhancing the light extraction efficiency of nanowire UV LEDs. Reference R. T. Velpula, B. Jain, M. R. Philip, et al., Sci. Rep., 10(1) 2547-2556 (2020).R. T. Velpula, B. Jain, H.Q.T. Bui, et al., Opt. Mater. Express, 10(2), 472-483 (2020).B. Jain, R. T. Velpula, M. Tumuna, et al., Opt. Express, 28(15), 22908-22918 (2020). Figure 1