Energy-gap modulation of BN ribbons by transverse electric fields: First-principles calculations

Systematic ab initio calculations show that the energy gap of BN nanoribbons (BNNRs) with zigzag or armchair edges can be significantly reduced by a transverse electric field and be completely closed at a critical field which decreases with increasing ribbon width. In addition, a distinct gap modulation in the ribbons with zigzag edges is presented when a reversed electric field is applied. In a weak field, the gap reduction of the BNNRs with zigzag edges originates from the field-induced energy level shifts of the spatially separated edge states, while the gap reduction of the BNNRs with armchair edges arises from the Stark effect. As the field gets stronger, the energy gaps of both types of the BNNRs gradually close due to the field-induced motion of nearly free electron states. Without the applied fields, the energy gap modulation by varying ribbon width is rather limited.