1. A method comprising: forming, in each memory cell of an array of memory cells, a passive layer adjacent to a first ohmic contact layer; forming an active layer adjacent to the passive layer, wherein one of the active layer and the passive layer is composed of a P-type material and one of the active layer and the passive layer is composed of an N-type material such that combining the layers forms a diodic junction; and forming a second ohmic contact layer adjacent to the active layer.