Direct Observation of Al Migration Enhancement by Changing the Al and N Source Relative Position in the Molecular Beam Epitaxy of AlGaN Nanowires

Abstract

Aluminum (Al)-containing nitrides, including AlN, AlScN, and AlGaN, are emerging material platforms for future-generation photonic, electronic, ferroelectric, and multifunctional semiconductor devices. Nonetheless, the low Al migration mobility in a nitrogen environment is a notorious hindrance to obtaining high-quality Al-containing nitride epilayers. This is particularly the case for the epitaxy of Al-containing nitrides with radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE), due to the use of relatively low substrate temperatures. As such, various approaches have been employed in promoting Al migration such as metal-modulated epitaxy (MME). Despite the progress, the effect of the relative position of the Al and N sources on the Al migration mobility has remained unclear. In this study, we show that MBE-grown AlGaN nanowires can be an effective probe to examine the effect of the Al and N source relative position on the Al migration mobility and demonstrate clearly that Al adatoms appear to be more mobile from the Al source that is far away from the N source, compared to those from the Al source that is near the N source. This study therefore can potentially impact the development of emerging Al-containing semiconductor devices by MBE. Moreover, the demonstrated correlated Al source dependent morphological and optical properties of AlGaN nanowires can naturally help the development of AlGaN-nanowire-based UV light-emitting diodes (LEDs) and lasers.