In: Chemistry
Stoichiometry related defects are common in ionic crystalline
thin films. Zinc sulfide (ZnS) is one of such II-VI semiconductor
ionic compounds composed of Zn that has an atomic number of 30 and
S that has an atomic number of 16. It is meant to deposit ZnS thin
film, for that film, please briefly discuss
(a) The possible mechanisms of point defect generation.
(b) The nonstoichiometric defects that would exist in that film how
it would affect the electric properties.
(c) Doping effects replacing either Zn or S sub-lattices.
(a)there are two methods of generation of point defect one is based on origin and another one based on position. origin based point defect can be further divided into two 1.statistical arises due to thermodynamic reason an 2.structural arises due to stoichiometric difference .position based point defects are divide into two 1.random :means atom swill not orient in a particular way,there is no order of arrangement of atoms and 2.ordered sub lattice
(b)if point defects are present then there is an increment in the electrical properties like conductivity increases,when there is dislocation of atoms in the lattice then electrons can move faster,if some atoms are missing then in that place an electron can come there by increase the conductivity.
(c)because sulfur atom needs more space to occupy in the lattice than zinc when doping occurs there is more chance fro sulfur to be replaced with the doping element.So that there is more generation of free space and there by it will enhance the conductivity.