Electronic Structure of Ternary Semimagnetic Semiconductors

Ternary semimagnetic semiconductors (ternary SMSC) are substitutional alloys in which random cations in a II-VI semiconductor lattice are replaced with a magnetic ion (usually Mn or Fe). These semiconductors can be formed by bulk growth techniques in large single phase, single crystals for a wide but limited range of stoichiometry. Interest in this class of semiconductors originates primarily from their composition dependent semiconducting properties and their novel magneto-optical and magneto-transport characteristics which lead to proposed optoelectronic device applications. We have performed a systematic study of the electronic properties of bulk semimagnetic ternary semiconductors with photoemission spectroscopy. Synchrotron radiation is used to analyze the Mn 3d contribution to the valence electronic structure as well as the influence of the Mn 3d states on the electronic states of the II-VI binaries which has been the subject of substantial debate. We address these issues by analyzing 3d-related structure in the ternary density of states, studying the composition dependence of the electronic states, Mn 3d-chalcogen p hybridization, and the relative importance of one-electron and multielectron effects in determining the experimental spectral features. The unoccupied Mn 3d states are vital for an understanding of the exchange interaction, the resulting magnetic properties, and for an optical characterization of the ternary SMSC alloys. We have conducted preliminary investigations of the excited electron states of Cd_{ rm 1-x}Mn_{rm x}Te with inverse photoemission spectroscopy in the Bremsstrahlung Isochromat Spectroscopy (BIS) mode. The Mn 3d spin splitting determined is significantly larger than predicted by first principles calculations, the implications of which are discussed. Finally, experiments are described in which metastable Cd_{rm 1-x}Mn _{rm x}Te alloys were fabricated in situ through interface reaction of CdTe with Mn thin films. This allowed for the investigation of the electronic structure of SMSC in the range of compositions not accessible with bulk crystal growth methods.