AB-INITIO CALCULATION FOR MGTE AND TRANSITION OF MGXCD1-XTE FROM DIRECT TO INDIRECT SEMICONDUCTOR

The ternary mixed crystal system MgxCd1-xTe has recently attracted int erest as a basic material for the blue laser diode. We use norm-conser ving pseudopotentials in connection with the local-density approximati on for ab initio calculations of the stable crystal structure and the lattice constant. Our results are in quantitative agreement with struc tural properties. The electronic band structure is calculated in depen dence on the composition x of the system by the virtual-crystal approx imation (VCA). We find a transition from direct to indirect energy gap for x = 0.7 in accordance with experimental data.