Zinc oxide light-emitting diodes: a review

This paper presents a compact survey of the various material schemes and device structures that have been explored in the quest toward developing light-emitting diodes (LEDs) based on zinc oxide (ZnO) and related II-oxide semiconductors. Both homojunction and heterojunction devices have been surveyed. Material for fabricating these devices has been grown with a number of different techniques, such as pulsed laser deposition, molecular beam epitaxy, metal-organic chemical vapor deposition, and atomic layer epitaxy. This review also features a self-contained introduction to materials science and device processing technologies that are relevant for fabricating ZnO LEDs. These topics include dry and wet etching, contact formation, and optical doping of ZnO. Due to the overwhelming importance of p-type doping of ZnO for making electronic and optoelectronic devices, a separate short section on electrical doping of ZnO is also included. The rest of this paper describes several different attempts at making blue- and ultraviolet-emitting ZnO LEDs. These include simple pn-junction devices as well as more complicated heterostructure devices incorporating charge carrier barriers and quantum wells. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)