(Invited) ScAlN: A Novel Barrier Material for High Power GaN-Based RF Transistors

ScAlN is a novel group IIIA/IIIB-N alloy gaining interest for acoustoelectric applications. The high piezoelectric coefficients that make ScAlN appealing for RF filters combined with high spontaneous polarization have the potential to open up a new class of microwave and millimeter-wave high-electron-mobility transistors (HEMTs) with high channel sheet charge density when ScAlN is used as the barrier layer. We present growth of ScAlN using molecular beam epitaxy (MBE) with an electron beam Sc source and show initial channel transport measurements. These initial demonstrations suggest MBE can be employed to grow ScAlN with sufficient crystal quality and chemical purity for use in electronic devices. ScAlN dry etch rates using standard Cl2-based reactive ion etching are much slower than AlN and GaN, enabling the use of ScAlN as a fluorine-free etch-stop layer. A simplified etch-stop process will enable passivation and gate recess processes to improve breakdown and reduce dispersion in RF HEMTs.