Direct evidence for a nonzero energy gap and half-metallicity in the diamondlike ferromagnet (Zn,Mn) GeP2

A giant narrowing of the energy gap in the nonlinear optical crystal ZnGeP₂ (ZGP) after the incorporation of manganese atoms into the chalcopyrite crystal lattice has been detected. The (Zn,Mn)GeP₂ (ZMGP) thin films grown by solid-phase endotaxy on ZGP (001) substrate share the tetrahedrally coordinated structure of chalcopyrite. The measured fine crystal structure and fundamental optical properties point to a semiconductor substance. However, other properties, such as electrical conductivity, current transport across the energy barrier ZMGP/ZGP, and photoemission of holes from the ferromagnetic ZMGP layer, claim that this substance is a metal. We investigated this unusual combination of properties in ZMGP using comprehensive measurements, including detailed chemical composition at the surface and in depth, and obtained direct experimental evidence for half-metallicity (HM) in the Mn-rich ZMGP material. Existing theories agree with these experimental proofs obtained. We discuss possible emitters of spin-polarized holes on these HM films operating at room temperature in fully diamondlike structures.