Defect Variation Zinc Oxide, ZnO

Zinc oxide is normally an w-type semiconductor with a narrow stoichiometry range. For many years it was believed that this electronic behavior was due to the presence of Zn (Zn+) interstitials, but it is now apparent that the defect structure of this simple oxide is more complicated. The main point defects that can be considered to exist are vacancies, V0 and VZn, interstitials, Oj and Zn, and antisite defects, 0Zn and Zno-Each of these can show various charge states and can occupy several different 

Calculations can provide information on the formation energy of these alternatives. Broadly speaking, the number of defects nd is related to the formation energy by an equation of the sort described in Chapter 2  

Chemically, this can be expressed in terms of defect formation equations. Taking the partial pressure of the zinc as dominant, zinc-rich material can be formulated by the capture of zinc atoms from the gas phase  

In this equation, the zinc is lost as atoms, not ions, and two electrons have to be donated to the Zn2+ for this to be possible, leaving two holes in the crystal. These holes can sit at the vacancy to create a neutral defect, VZn  

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