Surface passivation of light emitting diodes: From nano-size to conventional mesa-etched devices

III-V compound semiconductor-based light emitting devices (LEDs) operating in ultraviolet to visible wavelength ranges are greatly important for their applications, including displays, solid-state lighting, biomedical applications, optogenetics, and high bandwidth visible light communications. The performance of such LEDs is unavoidably affected by the surface characteristics of semiconductor layers. In particular, for LEDs, plasma-etching processes are inevitably adopted to define mesas, via holes and waveguides. The presence of surface defects is exceedingly detrimental to the device performance. It is therefore vital to understand the passivation mechanisms and approaches in order to control and so to maximize the efficiency. Here, we review recent progress in the surface treatment and passivation of III-V compound semiconductors-based LEDs. We show how different types of passivation approaches, including treatments with aqueous solutions, dielectric materials, or combination of both, affect the surface states and plasma-induced defects and hence the electrical and optical performance of LEDs.