When doped elements are added to metal oxides, it can change the dopant element's properties. For example, when Zn is added to TeO2 which is already a p-type, the dopant element can then be determined by measuring electrical properties such as the electron concentration and hole concentration. If the hole concentration is higher than the electron concentration, then the dopant is p-type, and if the electron concentration is higher, then the dopant is n-type.