Defect Control Strategies for Al(1-x)Gd(x)N Alloys

Tetrahedrally-bonded III-N and related alloys are useful for a wide range of applications, from optoelectronics to dielectric electromechanics. Heterostructural AlN-based alloys offer unique properties for piezoelectrics, ferroelectrics, and other emerging applications. Atomic-scale point defects and impurities can strongly affect the functional properties of materials, and therefore, it is crucial to understand the nature of these defects and mechanisms through which their concentrations may be controlled in AlN-based alloys. In this study, we employ density functional theory with alloy modeling and point defect calculations to investigate native point defects and unintentional impurities in Al(1-x)Gd(x)N alloys. Among the native defects that introduce deep mid-gap states, nitrogen vacancies (V_N) are predicted to be in the highest concentration, especially under N-poor growth conditions. We predict and experimentally demonstrate that V_N formation can be suppressed in thin films through growth in N-rich environments. We also find that Al(1-x)Gd(x)N alloys are prone to high levels of unintentional O incorporation, which indirectly leads to even higher concentrations of deep defects. Growth under N-rich/reducing conditions is predicted to minimize and partially alleviate the effects of O incorporation. The results of this study provide valuable insights into the defect behavior in wurtzite nitride-based alloys, which can guide their design and optimization for various applications.