LATTICE DYNAMICS OF A"BIVCX AND A1B"'C3j ' SEMICONDUCTORS WITH CHALCOPYRITE LATTICE IN A RIGID-ION MODEL

Rbumk.- Un modele d'ions ponctuels non polarisables relies par des forces A courte distance a leurs plus proches voisins a Cte applique I'ktude de la dynamique du rkseau et des propriktes optiques infrarouges associees des composCs chalcopyrites ZnSiPz, CdGePz et CuAIS2. La distribution des charges effectives entre les ions est en accord qualitatif avec celle qui derive de la theorie dielectrique de I'ionicite de Phillips. Les frequences actives en IR et les intensites d'oscillateurs sont en bon accord avec l'experience. La caracteristique la plus jnthressante des spectres calculCs est la presence de bandcs interdites. Abstract.- A model of unpolarizable point ions linked by short-range forces with their nearest neighbours is applied to the investigation of lattice dynamics and related optical properties in the infrared of chalcopyrite. Compounds ZnSiPz, CdGeP2 and CuAIS2. The distribution of effective charges between the ions agrees qualitatively with that which follows from Phillips ' dielectric theory of ionicity. IR-active frequencies and the oscillator strengths are in good agreement with the experiment. The most interesting feature of the calculated spectra is the presence of forbidden bands. A t the present time there is a considerable amount I