Crystal-field and spin-orbit interactions at the fundamental gap of AgGaSe2chalcopyrite compound

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Abstract
The authors have studied electronic transitions around the fundamental gap of AgGaSe2 by near-normal reflectivity measurements performed at 5K. The localisation of the fundamental and first excited states of the exciton associated with the gap makes it possible to determine the energy of this gap. The AgGaSe2 gap value is discussed in relation with those of its zincblende binary analogues. From the observation of three experimental structures in the region of the fundamental gap and using the quasi-cubic model. They propose values for the crystal-field and spin-orbit parameters. Experimental spin-orbit splitting is found to be smaller than splitting calculated from a model derived from those previously proposed. This spin-orbit splitting reduction is interpreted as being due to the hybridisation of the Se p and Ag d orbitals. Using a linear hybridisation model, they estimate the d-level hybridisation percentage. Also, an estimation for the deformation potential is proposed.