Molecular beam epitaxial growth of scandium nitride on hexagonal SiC, GaN, and AlN

Abstract

RF plasma assisted MBE growth of Scandium Nitride (ScN) thin films on GaN (0001)/SiC, AlN (0001)/Al2O3 and on 6H-SiC (0001) hexagonal substrates is found to lead to a face centered cubic (rock-salt) crystal structure with (111) out-of-plane orientation instead of hexagonal orientation. For the first time, cubic (111) twinned patterns in ScN are observed by in-situ electron diffraction during epitaxy, and the twin domains in ScN are detected by electron backscattered diffraction, and further corroborated with X-ray diffraction. The epitaxial ScN films display very smooth, sub nanometer surface roughness at a growth temperature of 750C. Temperature-dependent Hall-effect measurements indicate a constant high n-type carrier concentration of ~1x10 20 /cm 3 and electron mobilities of ~ 20 cm 2 /Vs.

High mobility and high thermoelectric power factor in epitaxial ScN thin films deposited with plasma-assisted molecular beam epitaxy

“…At room temperature, the ScN film having a thickness of 450 nm exhibited the highest mobility of 127 cm 2 /V s, with an associated n-type (electron) concentration of 8.6 Â 10 19 cm À3 , which resulted in a room-temperature electrical conductivity of 1759 Scm À1 . Such a high mobility obtained in PAMBE-deposited ScN is consistent with the previous reports 4,40,[48][49][50][51][52] of ScN growth by radical source MBE and is higher than the mobility obtained with previous sputterdeposited ScN (see Table I in supplementary material). It is important to note here that the measured mobility is high despite the presence of extended defects such as grain boundaries and dislocation networks that are known to scatter electrons strongly.…”

Co-sputtering of $$\hbox {Al}_{1-x}\hbox {Sc}_{x}\hbox {N}$$ thin films on Pt(111): a characterization by Raman and IR spectroscopies

“…could be related to the (111) plane of cubic ScN (ca. 34:5 [34,35]) if it is under large tensile strain. Such an interpretation seems more likely since the Al 1Àx Sc x N alloy with a Sc content !…”

Synthesis and study of ScN thin films

“…Since, fluorescence detected XAFS is known to be a bulk sensitive technique with penetration depth ranging in micrometers [51] compared to surface sensitive SXAS where the depth scale ranges only in nanometer scale (≈10 nm) [29], the averaged out bulk information from the XAFS data further confirms the presence of higher surface oxidation in the samples as was evidenced from the Sc L-edge and O Kedge SXAS spectra. [59] and Fm 3m [15], respectively. The fitting was performed using LP obtained from the XRD data and the obtained metrical parameters are tabulated in Table II.…”

“…Hence, the local co-ordination environment is rather in a distorted hexagonal symmetry which might be responsible for an intense pre-edge feature across the Sc K-edge absorption spectra (Figure 3). In addition, for ScN, considering a theoretical LP of a * = 4.501 Å [15,30], the first and second nearest neighbor distances can be anticipated at R * Sc−N = a/2 = 2.25 Å and R * Sc−Sc = a/ √ 2 = 3.18 Å [60]. As can be seen from Figure 4(a) and (b), the two consecutive maxima distributed over R-φ = 1 -3.9 Å range correspond to the first Sc-N and second Sc-Sc nearest neighbor bonds.…”

“…Hence for application based perspectives, to modulate the band structure engineering for superior device performances, so far, most of the studies adopted high vacuum (≤10 −8 Torr) depositions to ensure low defect concentrations with atomically smooth epitaxial growth of ScN thin film samples on variety of single crystal substrates (MgO, Al 2 O 3 , GaN, SiC etc.) [13][14][15][16], and few of them aided with process parameters are tabulated in Table I. As can be seen from Table I, conventional use of high substrate temperature (T s ≥ 823 K) has been an integral part during the synthesis of ScN thin film samples, possibly due to higher adatom mobility promoting enhanced crystalline defect free ScN growth [17].…”