Energy band structure of I–III–VI2 semiconductors

We review recent studies of the energy band structure of I-III-VI₂ semiconductors. The structure of the uppermost valence bands of a I-III-VI₂ compound is profoundly influenced by the proximity of noble metal d levels in the valence band. The direct energy gaps observed in I-III-VI₂ compounds are low relative to the energy gaps in the II–VI analogs by amounts up to 1.6eV, and the spin-orbit splittings observed in the ternaries are low relative to the values observed in the binary analogs, owing to a partial cancellation of the positive spin-orbit parameter for p levels and the negative spin-orbit parameter for d levels. The presence of the noble metal d levels in the valence band has been confirmed directly by the observation of electroreflectance structure due to transitions from the d levels themselves to the lowest conduction band minimum.