Trigonal paramagnetic interface defect in epitaxial Ge 3 N 4 / ( 111 ) Ge

We report on the observation by electron spin resonance (ESR) of an anisotropic paramagnetic defect at the interface of epitaxially grown Ge 3 N 4 / ( 111 ) Ge entities with nanometer thin Ge 3 N 4 layers. The defect exhibits trigonal C 3 v symmetry characterized by g ∥ ≈ 2.0023 and g ⊥ ≈ 2.0032 , and is observed most prominently after 10 eV optical excitation, with maximum areal density ≈ 2 × 10 11 cm − 2 . The defect is suggested to concern the Ge K-type center, its occurrence appearing inherent to the specific heteroepitaxial interface matching.