From Fully Strained to Relaxed: Epitaxial Ferroelectric Al1‐xScxN for III‐N Technology. (12th February 2022)

• Record Type: Journal Article
• Authors: Schönweger, Georg; Petraru, Adrian; Islam, Md Redwanul; Wolff, Niklas; Haas, Benedikt; Hammud, Adnan; Koch, Christoph; Kienle, Lorenz; Kohlstedt, Hermann; Fichtner, Simon
• Is Part Of: Advanced functional materials. Volume 32:Number 21(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-12
• Subjects: aluminum‐scandium‐nitride (Al 1‐xScxN) -- epitaxial growth -- ferroelectric -- gallium nitride -- semiconductors; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202109632
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: The recent emergence of wurtzite‐type nitride ferroelectrics such as Al1‐ 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 Al1‐ 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 Al1‐ x Sc x N films is discussed. Unlike in previously reported studies on ferroelectric Al1‐ 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. Abstract : Ferroelectric Al1‐ x Sc x N thin films epitaxially grown on doped n‐GaN/sapphire substrates by sputter epitaxy are reported. The interplay between the substrate and the film in terms of lattice (mis)match and polarity leads to the observation of previously unknown peculiarities in the ferroelectric response of wurtzite‐type ferroelectrics, such as initial multidomain states and piecemeal polarization reversal.