Surface and Bulk Conductivities of Cu2O Single Crystals

The surface and bulk conductivities of Cu2O crystals were measured using guard ring techniques on cleaved, polished and etched samples over a temperature range from +200°C to −170°C in air, vacuum, and helium atmosphere. The bulk conductivity followed the simple exponential temperature dependence of the typical semiconductor with a single activation energy of about 0.3 eV over the entire range. The temperature dependence of the surface conductivity appeared to consist of a number of activation energies, ranging from 0.1 to 0.3 eV. Heating to 180°C in air or vacuum can be used to minimize the surface contribution to the conductivity. It was found that polished surfaces are highly deceptive for standard measurements of transport effects.