Interstitial zinc in zinc oxide

Abstract

Methods of introducing interstitial zinc into single crystals of zinc oxide are described which involve heating the crystals in zinc vapor followed by rapid quenching. The interstitial zinc atoms act as donors with a low ionization energy and they are observed by the extra conductivity which they impart to the crystals. The solubility in atoms/cm 3 from saturated zinc vapor is : n=3.4 × 10 20exp(−0.65 e kT ) . This solubility leads to a reasonable value for the vibrational entropy of the interstitial atom. In the range 180–350°C the diffusion coefficient of the donor obeys: 2 D i= 5.3 × 10 −4exp(−0.55 e kT ) . From these results the parabolic rate constant for the oxidation of metallic zinc may be calculated and the results are in good agreement with previous observations. The results of the high temperature diffusion of radioactive zinc into zinc oxide are less easy to understand and it may be that interstitial zinc is not involved in this process. Evidence is advanced that the defects are interstitial zinc atoms and not oxygen vacancies. The donors normally present in zinc oxide are not interstitial zinc atoms, but may be chemical impurities.