An electrode (109) insulated from a compound semiconductor layer (102) and being in contact with an electrode (101) and a compound semiconductor layer (103) is provided. A lattice constant of the compound semiconductor layer (103) is smaller than both of a lattice constant of the compound semiconductor layer (102) and a lattice constant of a compound semiconductor layer (104), and a lattice constant of a compound semiconductor layer (107) is smaller than both of the lattice constants of the compound semiconductor layer (102) and the lattice constants of the compound semiconductor layer (104). A conduction band energy of the compound semiconductor layer (103) is higher than a conduction band energy of the compound semiconductor layer (104).