  Altermagnet is an emerging antiferromagnetic material subclass that exhibits
spin-splitting in momentum space without net global magnetization and
spin-orbit-coupling effect. In this work, we develop a model of thermal charge
injection across an altermagnet/semiconductor (AM/S) Schottky contact. We
obtain analytical expressions describing the spin-dependent thermionic current
injection across the AM/S contact under any arbitrary interface orientation
angles. Interestingly, the spin-contrasting Fermi surface of an altermagnetic
electrode enables spin-polarized current to be injected into a nonmagnetic
semiconductor even though the system has net-zero magnetization. Our findings
thus reveal an altermagntic mechanism to achieve spin injection without
involving ferromagnetic ordering. The AM/S Schottky contact proposed here shall
provide a potential altermagnetic building block of spintronic devices that are
resilient against stray magnetic field perturbation and inherently compatible
with ultracompact integration.
