Aluminum gallium nitride (AlGaN) ultrawide bandgap semiconductors have been attractive for their applications to disinfection, material identification, and ultraviolet (UV) curing, and for their potential to replace conventional mercury lamp based light sources. Remarkable progress has been made in the past decades from understanding material fundamentals to device performance improvement. Nonetheless, the enduring challenges related to high dislocation densities and poor p-type doping, among others, make AlGaN nanowires an alternative appealing platform. In this talk, I will discuss our recent development on the molecular beam epitaxy of AlGaN nanowires for deep UV light emitting devices.

First, I will show that by exploiting the compositional fluctuations in high Al content AlGaN nanowires in nitrogen-rich environment, electroluminescence (EL) at 207 nm can be obtained. Such EL emission is measured from the device top surface. As today it has remained challenging to obtain EL emission from the surface around this wavelength (i.e., near vacuum UV), such nanowires could offer an interesting approach to obtain surface emitting at near vacuum UV. I will further show that, by using graphene contact, the light output of surface emitting AlGaN nanowire deep UV LEDs can be improved. It is found that comparing to conventional metal contact, by using graphene contact the light output can be improved by a factor of two and the peak external quantum efficiency can be improved by a factor of four. Lastly, I will show that, by using nanowire template on Si substrate, AlN epilayers with a relatively smooth surface can be obtained, which further enables the formation of AlGaN epilayers with various Al contents on top. Such AlGaN epilayers are found to have high internal quantum efficiency, presumably due to a strong carrier localization effect. Current progress on device development using such an AlN on Si template will also be discussed.