Experimental evidence of the splitting of the AgGaS2uppermost valence bands by crystal-field and spin-orbit interaction

The AgGaS 2 fundamental gap has been determined from low-temperature reflectance measurements and the result is commented on in relation to previous experimental determinations. With the aim of resolving for the first time in AgGaS 2 the B and C structures that are expected to occur in the gap region, the authors have performed reflectance measurements at 5 K. From the experimental determination of the energy location of the transitions A and C, they have calculated the energy at which the B transition should take place. This value corresponds to the change of slope observed experimentally at 2.91 eV on the reflectance curve, which is then attributed to the B transition. Using the quasi-cubic model, they have determined the value of the crystal-field parameter, which is found to be smaller (in absolute value) than the value previously published for AgGaS 2 . This difference is attributed to the fact that, in previous determinations, no account was taken of spin-orbit splitting because of the non-resolution of the B and C structures. Finally, an estimation is proposed for the deformation potential of AgGaS 2 .