Tunneling diodes operate based on the principle of quantum tunneling, a phenomenon where particles pass through a barrier that they classically shouldn't be able to. In a tunneling diode, when a small forward bias is applied, electrons "tunnel" through the narrow depletion region from the conduction band of the n-type material to the valence band of the p-type material. This results in a peak current followed by a region of negative differential resistance as the bias voltage increases.
