Alignment of isovalent impurity levels: Oxygen impurity in II-VI semiconductors

The isovalent oxygen impurity levels in the II-VI semiconductors ZnSe:O, ZnTe:O, and CdTe:O are studied using a method based on first-principles total energy and large scale charge patching band structure calculations. We find that, unlike the general expectation that these levels line up in an absolute energy scale, the positions of the isovalent a(1)(O) level depend sensitively on the local environment around the impurity, thus, the a(1)(O) levels align approximately only in the common-cation systems, whereas in the common-anion systems, the levels do not align. These general chemical trends also apply to other isovalent impurity systems.