Strongly dispersive dielectric properties of high-ScN-fraction ScAlN deposited by molecular beam epitaxy

TL;DR

This study investigates the dielectric properties of high-ScN-fraction ScAlN thin films grown by MBE, revealing significant permittivity increases and strong frequency dispersion, with notable differences from sputtered films.

Contribution

It provides the first comprehensive dielectric characterization of high-ScN-fraction ScAlN films grown by MBE, highlighting fundamental differences from sputtered counterparts.

Findings

Permittivity increases with ScN fraction and frequency

Strong dielectric dispersion observed in MBE-grown films

Differences between MBE and sputtered films in dielectric behavior

Abstract

We present a comprehensive study of dielectric properties including complex permittivity, loss, and leakage of high-ScN-fraction ScAlN thin films grown using molecular beam epitaxy (MBE). Dielectric spectroscopy is carried out on high-ScN-fraction (30%-40% ScN fraction) samples from 20 Hz to 10 GHz. We find that real permittivity {\epsilon}' increases significantly with increasing ScN fraction; a trend confirmed by density functional theory. Further, {\epsilon}' is strongly dispersive with frequency and increasing ScN fraction, with values for Sc0.4Al0.6N varying from 150 down to 60 with increasing frequency. Loss, dispersion, and DC leakage current correspondingly increase with ScN fraction. The high {\epsilon}' and strongly dispersive behavior in MBE ScAlN are not observed in a sputter-deposited ScAlN control with a similar ScN fraction, highlighting fundamental differences between films produced by the two deposition methods. Microscopy and spectroscopy analyses are carried out on MBE- and sputter-deposited samples to compare microstructure, alloy, and dopant concentration.