Surface conductivity produced on zinc oxide by zinc and hydrogen

The conductivity of single crystals of zinc oxide can be greatly increased by exposing them to hydrogen or zinc vapor. Zinc can be adsorbed at room temperature, but hydrogen requires a temperature of 200°C to be effective. Oxygen destroys the excess conductivity at room temperature. It is concluded that the conductivity produced is associated with the crystal surface and arises from zinc atoms. Hydrogen may reduce the surface to produce the zinc. A surface conductivity of 1.5 × 10−4mhossquare role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{1.5 × 10}{}^{\mathrm{-4}}\text{mhos}\text{square}$$\text{1.5 × 10}{}^{\mathrm{-4}}\text{mhos}\text{square}$ can be attained. The surface conductivity varies with crystal diameter in the expected fashion, and it has been examined as a function of zinc pressure and of temperature. By quenching adsorbed zinc atoms the conductivity was observed down to liquid helium temperatures. The simple space charge theory for adsorbed donor atoms cannot explain all the observations, and it is probable that impurity band conduction is involved.