Zone‐centered phonons in AIBIIIS2 chalcopyrites

Abstract

The spectra of the zone‐centered phonons in five compounds of the A^IB^IIIS₂ chalcopyrite (ch) family are completed by IR absorption and Raman scattering measurements. The ch extended Keating model is applied to these phonons. The experiments and calculations clarify the assignments of the Γ₃‐modes and the low‐energy modes which originate from the transverse acoustic zincblende (zb) phonons. The central force constants between nearest neighbours α_BS of the homopolar bonds are very large corresponding to the small bond lengths. On the other hand, the strong heteropolar A–S bonds yield very low α_AS‐values. The model parameters, which are determined by optical phonon fitting, also reproduce in a zb approximation the elastic moduli of AgGaS₂.