Unification of the electrical behavior of defects, impurities, and surface states in semiconductors: Virtual gap states in CdO

In contrast to conventional semiconductors, native defects, hydrogen impurities, and surface states are all found to be donors in n-type CdO. Using this as a model system, the electrical behaviors of defects, dopants, and surface states in semiconductors are unified by a single energy level, the charge neutrality level, giving much insight into current materials and allowing a band-structure engineering scheme for obtaining desired custom electronic properties in new compound semiconductors.