1. A method comprising: providing a synaptic device including a first structure for injecting both electrons and holes into a semiconductor layer and traps for trapping both electrons and holes; receiving an electrical signal at the synaptic device, thereby causing the first structure to inject one of electrons and holes into the semiconductor layer, and effecting net negative charge trapping or net positive charge trapping within the traps upon injection of the one of electrons and holes into the semiconductor layer, wherein the first structure includes a contact region adjoining the semiconductor layer and the semiconductor layer comprises an organic layer containing the traps, the contact region injecting one of the electrons and holes into the semiconductor layer.