Enhanced Permittivity in Wurtzite ScAlN through Nanoscale Sc Clustering

TL;DR

This study demonstrates that nanoscale Sc-rich clusters in ScAlN films significantly enhance dielectric permittivity, with implications for tailoring ferroelectric and piezoelectric properties through nanoscale engineering.

Contribution

It reveals the presence of nanoscale Sc-rich clusters in ScAlN films and links their formation to enhanced dielectric permittivity, offering a new approach for property optimization.

Findings

MBE-grown films show stronger Sc clustering than sputtered films.

MBE-grown Sc0.3Al0.7N exhibits roughly double the permittivity of sputtered films.

Sc-rich clusters locally reach x ~ 0.5, near the ferroelectric transition point.

Abstract

ScN alloyed AlN (ScxAl1-xN, ScAlN) is a wurtzite semiconductor with attractive ferroelectric, dielectric, piezoelectric, and optical properties. Here, we show that ScAlN films (with x spanning 0.18 to 0.36) contain nanoscale Sc-rich clusters which maintain the wurtzite crystal structure. While both molecular beam epitaxy (MBE) and sputter deposited Sc0.3Al0.7N films show Sc clustering, the degree of clustering is significantly stronger for the MBE-grown film, offering an explanation for some of the discrepancies between MBE-grown and sputtered films reported in the literature. Moreover, the MBE-grown Sc0.3Al0.7N film exhibits a dispersive and anomalously large dielectric permittivity, roughly double that of sputtered Sc0.3Al0.7N. We attribute this result to the Sc-rich clusters locally reaching x ~ 0.5 and approaching the predicted ferroelectric-to-paraelectric phase transition, resulting in a giant (local) enhancement in permittivity. The Sc-rich clusters should similarly affect the piezoelectric, optical, and ferroelectric responses, suggesting cluster-engineering as a means to tailor ScAlNs functional properties.