Indium was dissolved in ZnO single crystals by coating crystals with a solution of indium nitrate and firing at temperatures between 800 and 1300C. The diffusion rate may be obtained by following the increase of conductivity produced by the indium as a function of time. The conductivity of a crystal supersaturated with respect to indium fell at a rate which indicated internal precipitation of a new phase occurring along lines. These lines were tentatively identified as being dislocations, and the results, interpreted according to the treatment of Frisch, indicated that crystals grown in the laboratory had a dislocation density near to 107/cm2, while some commercial crystals had a density near to 106/cm2. The diffusional behavior around the new phase was highly reproducible and, in air, gave:

D(cm2/s) ≈ 2.5 x 102exp[-3.16(eV)/kT]

The diffusivity was found to increase with increasing oxygen pressure as P021.4;

indicating that zinc vacancies controlled diffusion. The solubility of indium varied approximately as P02-1.8, as was to be expected if the indium dissolves in ZnO without being associated with a comparable concentration of vacancies. Hall-effect measurements indicated solubilities in the range of 1017 to 2 x 1019/cm3 and showed that the precipitated phase materially lowered the electron mobility.

The Diffusion and Precipitation of Indium in Zinc Oxide. Thomas, D.G.: Journal of Physics and Chemistry of Solids, 1959, 9[1], 31-42. See also: Journal of Chemical Physics, 1956, 25, 1136