▎ 摘　　要

We study the electronic properties of graphene nanoribbons with zigzag and armchair edges under a parallel electric field generated by two planar electrodes with a potential barrier simulating an insulating layer of electrodes in a FET structure using density functional theory combined with an effective screening medium method. Our calculations show that the nearly free electron (NFE) states strongly depend on the mutual arrangements of graphene nanoribbons with respect to the electric field. In contrast, the electronic energy bands associated with the pi electrons are insensitive to the relative direction of the ribbon with respect to the external electric field. We also observe that the electric field concentration around the edges leads to the orientation dependence of the NFE states on the field. (C) 2016 The Japan Society of Applied Physics