1. A semiconductor device comprising: a first electrode; a first layer containing a first metal oxide formed over and being in direct contact with the first electrode; a second layer containing a second metal oxide formed over and being in direct contact with the first layer containing the first metal oxide; a layer containing an organic compound formed over and being in direct contact with the second layer containing the second metal oxide; and a second electrode formed over and being in contact with the layer containing an organic compound, wherein the first layer containing the first metal oxide and the second layer containing the second metal oxide form a p-n junction.