  Zirconia (ZrO2) and hafnia (HfO2) are leading candidates for replacing SiO2
as the gate insulator in CMOS technology. Amorphous versions of these materials
(a-ZrO2 and a-HfO2)) can be grown as metastable phases on top of a silicon
buffer; while they tend to recrystallize during subsequent annealing steps,
they would otherwise be of considerable interest because of the promise they
hold for improved uniformity and electrical passivity. In this work, we report
our theoretical studies of a-ZrO2 and a-HfO2 by first-principles
density-functional methods. We construct realistic amorphous models using the
``activation-relaxation'' technique (ART) of Barkema and Mousseau. The
structural, vibrational, and dielectric properties of the resulting models are
analyzed in detail. The overall average dielectric constant is computed and
found to be comparable to that of the monoclinic phase.
