Impact and mitigation of surface oxides on aluminum nitride substrates

Surface oxides on AlN are shown to result in a dense layer of stacking faults that create dislocations at the regrowth interface, and ex situ cleaning methods are demonstrated to not be sufficient to achieve pristine surfaces on AlN substrates for the purpose of epitaxy. Low-temperature Al-flashing is found to mitigate the effects of surface oxides on regrown AlN films. Despite not fully removing the surface oxides – instead gettering them into sparse amorphous clusters that can be easily overgrown – Al-flashed films are shown to have lower dislocation densities than non-flashed films via x-ray diffraction and transmission electron microscopy. Additionally, in situ characterization techniques are shown to give crucial real-time feedback on the status of the Al-flashing process. The presence of surface-oxide-induced threading dislocations is correlated with an anomalous kink in the pre-turn on portion of the forward current density–voltage characteristics of AlN pn diodes while Al-flashed devices free of these additional dislocations are shown to not contain this anomalous kink. The successful removal of this anomalous feature by low-temperature Al-flashing represents a major step in understanding the electrical performance of emerging AlN-based devices.