Molecular beam epitaxy growth and characterization of ScGaN epilayers

Scandium (Sc) containing III-nitrides (Sc-III-nitrides) have emerged as a new member of the ferroelectric material family. Recent years have also witnessed the exploration of Sc-III-nitrides for device applications beyond ferroelectrics, e.g., photonic devices. In this context, it is important to understand the optical properties of Sc-III-nitrides. Herein, we report the molecular beam epitaxy growth and characterization of ScxGa1-xN (ScGaN) epilayers on AlN-on-sapphire template over a wide range of Sc contents from x = 0.08 to 0.50. Notably, the room temperature photoluminescence (PL) is reported for the first time from ScGaN epilayers, and its correlation to the structural properties as well as the underlying PL emission mechanisms are further discussed. Briefly, room temperature photoluminescence is measured for the samples with x < 0.33, and no defect PL is measured in the visible range. The PL peak energies further correlate very well to the optical bandgap energies derived from the ultraviolet-vis absorbance experiments. These energies are consistent with the transmission electron microscopy studies in that the majority phase of the present epilayers is wurtzite (WZ). Nonetheless, these energies are smaller than the theoretical predictions for the ScGaN epilayers in the pure WZ phase. Besides the presence of the zincblende phase nanoclusers and additional strain effects being the reasons, the presence of defect states within the bandgap could be another reason. These unveiled corrected structural and optical properties could facilitate the development of the Sc-III-nitride based devices beyond ferroelectrics.