Excitation to defect-bound band edge states in two-dimensional semiconductors and its effect on carrier transport

The ionization of dopants is a crucial process for electronics, yet it can be unexpectedly difficult in two-dimensional materials due to reduced screening and dimensionality. Using first-principles calculations, here we propose a dopant ionization process for two-dimensional semiconductors where charge carriers are only excited to a set of defect-bound band edge states, rather than to the true band edge states, as is the case in three-dimensions. These defect-bound states have small enough ionization energies but large enough spatial delocalization. With a modest defect density, carriers can transport through band by such states.