The conductivity of ZnO depends significantly on its content of charge carriers, which is in turn highly influenced by its stoichiometry. The latter can be adjusted by the oxygen or zinc partial pressure during high temperature processing. In addition, annealing in a reducing atmosphere containing hydrogen can have a large effect on electrical conductivity. In contrast, hydrothermally grown ZnO crystals show very high resistivities due to the solvents used containing atoms such as Na, K or Li that can readily provide charge compensation in a defective lattice . Electrical conductivity of ZnO, as in most other semiconductors, increases with temperature.