Search

Thickness scaling of ferroelectricity in Al1−xScxN is a determining factor for its potential application in neuromorphic computing and memory devices. In this letter, ultrathin (10 nm) Al0.72Sc0.28N films that are ferroelectrically switchable at room temperature are reported on. All‐epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering onto GaN/sapphire substrates followed by an in situ Pt capping approach to avoid oxidation of the Al0.72Sc0.28N film surface. Structural characterization by X‐Ray diffraction and transmission electron microscopy reveals the established epitaxy. The thus‐obtained high‐quality films in combination with in situ capping facilitate ferroelectric switching of Al1−xScxN in the ultrathin regime. The analysis of the relative permittivity and coercive field dependence on Al0.72Sc0.28N film thicknesses in the range from 100 nm down to 10 nm indicates only moderate scaling effects, suggesting that the critical thickness for ferroelectricity is not yet approached. Furthermore, the deposited layer stack demonstrates the possibility of including ultrathin ferroelectric Al1−xScxN into all‐epitaxial GaN‐based devices using sputter deposition techniques. Thus, the integration and scaling potential of all‐epitaxial ultrathin Al1−xScxN offering high storage density paired with low‐voltage operation desired for state‐of‐the‐art ferroelectric memory devices are highlighted. [ABSTRACT FROM AUTHOR]

The recent emergence of wurtzite‐type nitride ferroelectrics such as Al1‐xScxN has paved the way for the introduction of all‐epitaxial, all‐wurtzite‐type ferroelectric III‐N semiconductor heterostructures. This paper presents the first in‐depth structural and electrical characterization of such an epitaxial heterostructure by investigating sputter deposited Al1‐xScxN solid solutions with x between 0.19 and 0.28 grown over doped n‐GaN. The results of detailed structural investigations on the strain state and the initial unit‐cell polarity with the peculiarities observed in the ferroelectric response are correlated. Among these, a Sc‐content dependent splitting of the ferroelectric displacement current into separate peaks, which can be correlated with the presence of multiple strain states in the Al1‐xScxN films is discussed. Unlike in previously reported studies on ferroelectric Al1‐xScxN, all films thicker than 30 nm grown on the metal (M)‐polar GaN template feature an initial multidomain state. The results support that regions with opposed polarities in as‐grown films do not result as a direct consequence of the in‐plane strain distribution, but are rather mediated by the competition between M‐polar epitaxial growth on an M‐polar template and a deposition process that favors nitrogen (N)‐polar growth. [ABSTRACT FROM AUTHOR]