Structural properties and epitaxial relation of cubic rock salt ScxAl1−xN/ScN/Si

Abstract

ScN in the rock salt structure is a well-investigated material due to its desirable properties like the high hardness or large thermal conductivity. Recent computations by Adamski et al. [Appl. Phys. Lett. 115, 232103 (2019)] showed that ScN/GaN heterostructures exhibit an outstanding polarization gradient which would be beneficial for polarization induced electron gases. The pseudobinary semiconductor ScxAl1−xN, when maintaining the cubic rock salt structure, could be beneficial for tailoring the polarization gradient using the Sc dependency of material properties. The structural properties of rs-ScxAl1−xN are not fully discovered yet, thus in this work, DC-magnetron sputtered cubic rock salt ScxAl1−xN thin films with 0.55<x<1.00 were grown and analyzed on ScN(111)/Si(111). The epitaxial relation of ScN(111) thin films on the Si(111) substrate is determined to be ScN[110] ∥ Si[100]. Furthermore, concentration dependent properties like the lattice parameter of ScxAl1−xN were measured [a(ScN) = 4.50 Å, a(Sc0.55Al0.45N) = 4.30 Å] and the stress σ within the layers was determined. The crystal quality was evaluated using ω-scans, revealing FWHM=1.14° for Sc0.95Al0.05N. The diameters of the columns were determined by atomic force microscopy and scanning electron microscopy and they are range from 34 to 59 nm for 0.55<x<1.00. At x=0.55, ScxAl1−xN columns in the hexagonal wurtzite as well as cubic rock salt structure were detected. This information about the structural specifications of ScxAl1−xN in the rock salt structure forms the basis for further investigations and experimental confirmation of the electric properties of ScN/GaN heterostructures or even a ScxAl1−xN/GaN based approach for improved structures for high-electron-mobility transistors.