A multifrequency electron spin resonance (ESR) study of Ge3N4/(111)Ge entities with rim thick epitaxial Ge3N4 layers. of subcritical thickness for mismatch relaxation, grown in a nitrogen plasma reveals the presence of an anisotropic paramagnetic interface center of trigonal symmetry. Building on the analysis of its specific ESR properties. including magnetic field angular mapping data and in the light or previous light the signal is tentatively ascribed to the interfacial Ge-center dot N-3 center The defect occurrence is discussed within the specific interface matching, without misfit dislocations As an interfacial Ge dangling bond defect. it may operate as an inherent electrically detrimental trap. (C) 2009 Elsevier B.V. All rights reserved