A semiconductor wafer includes a first semiconductor, and a second semiconductor formed directly or indirectly on the first semiconductor. The second semiconductor contains a first impurity atom exhibiting p-type or n-type conductivity, and a second impurity atom selected such that the Fermi level of the second semiconductor containing both the first and second impurity atoms is closer to the Fermi level of the second semiconductor containing neither the first impurity atom nor the second impurity atom, than the Fermi level of the second semiconductor containing the first impurity atom is. For example, the majority carrier of the second semiconductor is an electron, and the Fermi level of the second semiconductor containing the first and second impurity atoms is lower than the Fermi level of the second semiconductor containing the first impurity atom.