Provided are a light-receiving element which has more capability of detecting wavelengths than that of existing silicon light-receiving elements and a unit pixel of an image sensor by using it. The light-receiving element includes: a light-receiving unit which is floated or connected to external voltage and absorbs light; an oxide film which is formed to come in contact with a side of the light-receiving unit; a source and a drain which stand off the light-receiving unit with the oxide film in between and face each other; a channel which is formed between the source and the drain and forms an electric current between the source and the drain; and a wavelength expanding layer which is formed in at least one among the light-receiving unit, the oxide film and the channel and forms a plurality of local energy levels by using strained silicon.

A pixel structure comprising: a diode body comprising: a base portion protruding from a substrate and a main portion on top of the base portion, wherein a footprint of the base portion is smaller than a footprint of the main portion, and wherein the main portion comprises first and second oppositely doped regions formed in a top portion of the main portion, wherein the first and second doped regions are formed in a central part and along a periphery, respectively, of the footprint of the main portion; a gate arranged to circumferentially surround the diode body, comprising a first gate portion surrounding the main portion and a second gate portion protruding inwardly from the first gate portion to undercut the main portion and surround the base portion; a gate dielectric layer arranged to separate the gate and the diode body; and first and second diode terminals, and a gate terminal.

An optoelectronic device comprises a gapped graphene system (GGS) a top gate electrode, a bottom gate electrode and a controller configured for applying a voltage bias between the gate electrodes to effect a bandgap in the GGS, wherein the bandgap is selected to allow the GGS to receive or emit light having a terahertz frequency.