CO IMPURITY EFFECT IN ZN1-XCOXSE CRYSTALS GROWN UNDER EQUILIBRIUM CONDITION

The influences of Co impurity in the Zn1-xCoxSe crystal were investiga ted by X-ray diffractometry (XRD) and Raman spectroscopy using melt gr own Zn1-xCoxSe polycrystals. The solid solubility of Co atom in melt g rown ZnSe crystal is about x= 0.02 +/- 0.0015. The solid solubility of magmetic ions may depend on the electronegativity and covalent radius . It was found that the lattice constant of the crystal increases line arly up to x = 0.0086 and then saturates as the amount of Co impurity increases. It is also observed that the TO2 and LO1 Raman modes in Zn1 -xCoxSe grown under equilibrium condition soften in the value of x < 0 .0086 by the addition of Co atoms. There is a linear relationship betw een the ionicity and the oscillator strength which is calculated using the energies of TO2 and LO1 phonon modes with the slope of -7.02 x 10 (25) (s-2). From these observations it is clear that the instability of Zn1-xCoxSe crystal is mainly due to the ionicity difference between Zn and Co atoms since both covalent radii are almost the same.