From Fully Strained to Relaxed: Epitaxial Ferroelectric Al1‐xScxN for III‐N Technology

The recent emergence of wurtzite‐type nitride ferroelectrics such as Al 1‐ x Sc x N 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 Al 1‐ x Sc x N 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 Al 1‐ x Sc x N films is discussed. Unlike in previously reported studies on ferroelectric Al 1‐ x Sc x N, 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.