Nature of the interface of (1 0 0)Ge/insulator structures with ultrathin HfO2 and GeOx(Ny) layers probed by electron spin resonance

Electron spin resonance (ESR) in combination with electrical analysis indicates basic differences in the defect properties of the (1 0 0)Ge/GeOxNy/HfO2 and (1 0 0)Ge/GeO2 interfaces with the seemingly isomorphic interfaces of (1 0 0)Si with the HfO2 and SiO2. ESR fails to reveal dangling bond centers associated with Ge crystal surface atoms—only paramagnetic defects originating from the near-interfacial Ge oxide or Ge (oxy)nitride layers are observed. In contrast to the amphoteric Pb-type centers (Si dangling bonds) commonly observed at the silicon/insulator interfaces, the major component of the Ge/insulator interface trap spectrum comes from slow acceptor states which appear resistant to passivation by hydrogen and show no immediate correlation with the observed paramagnetic centers.