Layer dependence of defect charge transition levels in two-dimensional materials

Abstract

Point defects in two-dimensional (2D) materials hold great promise for optoelectronic and quantum technologies. Their properties depend sensitively on the dielectric environment and number of 2D layers, but this has remained a challenge to include in first-principles calculations on account of the high computational cost. Recent first-principles techniques facilitate efficient prediction of substrate effects on defect charge transition levels in 2D materials, replacing the substrate by a continuum dielectric model. Here, we show that analogous continuum treatment of defect-free layers in multilayer 2D materials accurately predicts defect energies compared to explicit multilayer calculations, but at a small fraction of the computational cost. Applications of this technique to one- to five-layer and bulk hexagonal boron nitride reveal that defect ionization energies systematically decrease with an increasing number of layers and for defects in inner layers due to increased dielectric screening. Our results highlight the dominant role of electrostatic screening in the effect of the environment and the feasibility of tuning defect levels in 2D materials using material thickness and defect location within the material.