  Half-Heusler(HH) alloys have shown promising thermoelectric properties in the
medium and high temperature range. To harness these material properties for
thermoelectric applications, it is important to realize electrical contacts
with low electrical contact resistivity. However, little is known about the
detailed structural and electronic properties of such contacts, and the
expected values of contact resistivity. Here, we employ atomistic ab initio
calculations to study electrical contacts in a subclass of HH alloys consisting
of the compounds HfCoSb, HfZrCoSb, and HfZrNiSn. By using Ag as a prototypical
metal, we show that the termination of the HH material critically determines
the presence or absence of strong deformations at the interface. Our study
includes contacts to doped materials, and the results indicate that the p-type
materials generally form ohmic contacts while the n-type materials have a small
Schottky barrier. We calculate the temperature dependence of the contact
resistivity in the low to medium temperature range and provide quantitative
values that set lower limits for these systems.
