Young’s modulus, Poisson’s ratio, and residual stress and strain in (111)-oriented scandium nitride thin films on silicon

Abstract

Epitaxial scandium nitride films (225nm thick) were grown on silicon by molecular beam epitaxy, using ammonia as a reactive nitrogen source. The main crystallographic orientation of ScN with respect to Si is (111)ScN‖(111)Si and [1–10]ScN‖[0–11]Si; however, some twinning is also present in the films. The films displayed a columnar morphology with rough surfaces, due to low adatom mobility during growth. The strain-free lattice parameter of ScN films grown under optimized conditions was found to be 4.5047±0.0005Å, as determined using high-resolution x-ray diffraction (HRXRD). In-plane and out-of-plane strains were subsequently evaluated using HRXRD and were used to determine the Poisson ratio of ScN along the ⟨111⟩ direction, which is found to be 0.188±0.005. Wafer curvature measurements were made and combined with the strain information to determine the average Young’s modulus of the films, which is found to be 270±25GPa. Residual film stresses ranged from −1to1GPa (depending on film growth temperature and film thickness) due to competition between the tensile stress (induced by the differential thermal contraction between the ScN film and the Si substrate) and intrinsic compressive stresses generated during growth.

HVPE of scandium nitride on 6H–SiC(0001)

“…The average thicknesses of the layers were calculated from the mass change that occurred during deposition, taking the density of ScN to be 4.276 g/cm 3 . These were confirmed by measuring the films' thickness directly by examining the edges of cleaved cross-sections.…”

“…Although ScN films have been prepared by a number of techniques including sputtering [6] and molecular beam epitaxy (MBE) [3,4,[7][8][9] [12,14]. In seminal studies, Dismukes et al [12,14] thoroughly characterized the properties of ScN films deposited by HVPE.…”

“…Scandium nitride (ScN) is especially interesting, due to its low lattice constant mismatch with gallium nitride (0.1% in the (1 1 1) plane) [3]. Combinations of ScN and GaN which have been proposed or prepared include ScN buffer layers for GaN on Si substrates [4], ScN-GaN superlattices [5], ScN-GaN heterojunctions [6] and alloys [7][8][9].…”

“…The normal crystal structure for ScN is rock salt with a lattice constant of 4.505 Å [3], but its metastable hexagonal form is predicted to have a very high piezoelectric coefficient [13]. A high solubility of manganese in ScN and a predicted high Curie temperature make ScN a good candidate for a ferromagnetic semiconductor [2].…”

Compensation of native donor doping in ScN: Carrier concentration control and p-type ScN

“…Scandium nitride (ScN) is a promising group III(B)-V indirect bandgap rocksalt semiconductor [1][2][3][4][5][6][7] with octahedral coordination. ScN thin films have attracted significant interest in recent years for their potential applications in thermoelectricity [8][9][10] , as a semiconducting component material in epitaxial single crystalline nitride metal/semiconductor superlattices [11][12][13][14][15] , and as an interlayer for the growth of high quality GaN based devices 16 with reduced dislocation densities [17][18] .…”