Low leakage current in heteroepitaxial Al0.7Sc0.3N ferroelectric films on GaN

Wurtzite (Al,Sc)N ferroelectrics are attractive for microelectronics applications due to their chemical and structural compatibility with wurtzite semiconductors, such as GaN and (Al,Ga)N. However, the leakage current in epitaxial stacks reported to date should be reduced for reliable device operation. Here, we demonstrate low leakage current in epitaxial Al0.7Sc0.3N films on GaN with well-saturated ferroelectric hysteresis loops that are orders of magnitude lower (i.e., 0.07 A cm−2) than previously reported films (1–19 A cm−2) having similar or better structural characteristics. We also show that, for these high-quality epitaxial (Al,Sc)N films, structural quality (edge and screw dislocations), as measured by diffraction techniques, is not the dominant contributor to leakage. Instead, the small leakage in our films is limited by thermionic emission across the interfaces, which is distinct from the large leakage due to trap-mediated bulk transport in the previously reported (Al,Sc)N films. To support this conclusion, we show that Al0.7Sc0.3N on lattice-matched In0.18Ga0.82N buffers with improved structural characteristics but higher interface roughness exhibit increased leakage characteristics. This demonstration of low leakage current in heteroepitaxial (Al,Sc)N films and understanding of the importance of interface barrier and surface roughness can guide further efforts toward improving the reliability of wurtzite ferroelectric devices.