I understand that there is a presence of surface defects due to presence of dangling bonds. A Silicon atom at the surface will not have a nearest neighbour to bond with and it will have a space for one electron, thus giving rise to a defect which can act as an electron recombination site. Since the Silicon atom is positively charged when there is no electron in the defect state, it can be called a donor-like state.

I am however unable to understand what acceptor-like states mean? It is mentioned that these states are negatively charged when occupied. I am not able to use the logic of an electron-hungry Silicon atom at the surface to explain acceptor-like states.

Please shed some light on the origin of these two different types of defect states.

Image taken from: doi.org/10.1088/1674-4926/31/11/114005