1. A method for fabricating a memory device, comprising: forming a two-terminal memory layer above a substrate layer; including in the two-terminal memory layer an ohmic contact layer above the substrate layer, a resistive layer above the ohmic contact layer, a resistive switching material (RSM) layer above the resistive layer, and an active metal layer above the RSM layer; including a first semiconductor material layer in an amorphous phase in the resistive layer; and including a second semiconductor material layer in a polycrystalline phase in the resistive layer situated above the first semiconductor layer.