  Heuslers are a prominent family of multi-functional materials that includes
semiconductors, half metals, topological semimetals, and magnetic
superconductors. Owing to their same crystalline structure, yet quite different
electronic properties and flexibility in chemical composition, Heusler-based
heterostructures can be designed to show intriguing properties at the
interface. Using electronic structure calculations, we show that two
dimensional electron or hole gases (2DEG or 2DHG) form at the interface of
half-Heusler (HH) semiconductors without any chemical doping. We use
CoTiSb/NiTiSn as an example, and show that the 2DEG at the TiSb/Ni(001)
termination and the 2DHG at the Co/TiSn(001) termination are intrinsic to the
interface, and hold rather high charge densities of 3x10^14 carriers/cm^2.
These excess charge carriers are tightly bound to the interface plane and are
fully accommodated in transition-metal d sub-bands. The formation of 2DEG and
2DHG are not specific to the CoTiSb/NiTiSn system; a list of combinations of HH
semiconductors that are predicted to form 2DEG or 2DHG is provided based on
band alignment, interface termination, and lattice mismatch.
