FIG. 13(a) is a table showing examples of inorganic oxides included in a common electron-transport layer, and densities of the oxygen atoms in the inorganic oxides. FIG. 13(b) is a table showing examples of typical inorganic oxides and densities of the oxygen atoms in the typical inorganic oxides. Note that the inorganic oxides listed in FIG. 13(a) are n-type semiconductors, and the inorganic oxides listed in FIG. 13(b) are insulators.
FIG. 14 is a table showing materials to be selected for the oxide layer (the HTL) 74a from among the examples of the inorganic oxides included in the common electron-transport layer illustrated in FIG. 13(a), and materials to be selected for the oxide layer 74b from among the examples of the typical inorganic oxides listed in FIG. 13(b).
In this embodiment, the density of the oxygen atoms in the oxide layer 74a is lower than the density of the oxygen atoms in the oxide layer 74b. Hence, if the oxide layer 74a is formed of an inorganic oxide containing zinc oxide, the oxide layer 74b can be formed of an inorganic oxide (an oxide of a fifth group) containing at least one of aluminum oxide, gallium oxide, tantalum oxide, zirconium oxide, hafnium oxide, magnesium oxide, germanium oxide, silicon oxide, or a complex oxide containing two or more kinds of cations of these oxides.
