Tunneling Properties versus Electronic Structures in Si/SiO₂/Si Junctions from First Principles

Eunjung Ko, Kwang-Ryeol Lee, Hyoung Joon Choi
 

Using first-principles calculations, we study tunneling properties and electronic structures of Si(001)/SiO₂/Si(001) junctions in a wide energy range covering the local energy gap in the SiO2 regions. We show that the tunneling spectra T (E) as functions of energy E have overall similarity to the projected densities of states (PDOS) at the centers of the SiO₂ regions, but T (E) and PDOS have significant difference in their dependences on the SiO₂ thickness. From the energy dependences of T (E) and PDOS, distinctive energy ranges are recognized in the valence and conduction bands, reflecting the local electronic structures in the SiO₂ region induced from the Si regions. From the difference in the SiO₂-thickness dependences of T (E) and PDOS and from eigenchannel analysis, we find that the tunneling wavefunction inside the SiO₂ region decreases with a decay rate which itself decreases as the tunneling distance increases, resulting in a smaller averaged decay rate per length for a thicker SiO₂ region. These results provide a rich picture for the SiO₂ barrier in the aspects of tunneling and local electronic structures, and a theoretical framework generally applicable to other tunneling barriers.