Fabrication of HfO2/TiO2-based conductive distributed Bragg reflectors: Its application to GaN-based near-ultraviolet micro-light-emitting diodes

Abstract

Distributed Bragg reflector (DBR) has been used to enhance the performance of various optoelectronic devices because of its higher reflectance than metal reflector, particularly at a specific wavelength. However, the insulating property of the DBR structure have limited its use where the current injection is required (e.g., below electrodes). Here, we introduce a way to overcome this limit, by creating conductive paths in the DBR-electrode structure using an electrical breakdown process; thereby, achieving an ohmic contact with p-GaN contact layers, and finally apply to ultraviolet micro-light-emitting diodes (mu LEDs) to verify the validity of the method. Specifically, by inserting three pairs of TiO2/HfO2 -based conductive DBR structures under a Cr/Ni/Au-based p-type electrode, the reflectance of the p-type electrode was increased up to 95%, simultaneously increasing the output power of the mu LED by 5% by reducing the light absorption at the p-type electrode by the reflection of light without electrical losses. This approach is expected to offer a great flexibility in the design of conventional devices using DBR structures. (C) 2018 Elsevier B.V. All rights reserved.