Unit pixel of image sensor and light-receiving element thereof
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.
1. An image sensor unit pixel, comprising:
a light-receiving element which generates an electric current by using change of electric charge quantity caused by incident light; and
a reset element which removes residual electric charges from the light-receiving element,
wherein the light-receiving element comprises:
a light-receiving unit which absorbs light;
an oxide film which contacts 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 the source and the drain, and the source and the drain facing each other;
a channel region formed between the source and the drain such that an electric current can be formed between the source and the drain; and
at least one wavelength expanding layer, formed in at least one among the light-receiving unit, the oxide film, and the channel region, and the at least one wavelength expanding layer split energy levels to form a plurality of local energy levels,
wherein the wavelength expanding layer splits the energy levels of a conduction band and a valence band according to a direction of a crystal lattice arrangement of the wavelength expanding layer.
2. The image sensor unit pixel of claim 1 , wherein the light-receiving element is formed on a silicon substrate in which first-type impurities are doped.
3. The image sensor unit pixel of claim 2 , wherein the source and the drain are formed on a well in which second-type impurities are doped and the well is floated.
4. The image sensor unit pixel of claim 1 , further comprising:
a plurality of the wavelength expanding layers, which are different from each other in terms of at least one of their formation location and manufacturing process.
5. The image sensor unit pixel of claim 1 , wherein the wavelength expanding layer is formed by bonding heteroatoms to or injecting ions into a silicon crystal which forms the light-receiving unit or the channel region.
6. The image sensor unit pixel of claim 1 , further comprising:
a terminal which applies gate voltage to the light-receiving unit so as to control the threshold voltage and any output signals by controlling a gap between a Fermi level and an intrinsic level of the channel region.
7. The image sensor unit pixel of claim 1 , wherein the reset element removes residual charges from a diffusion well where the light-receiving element is formed.
8. The image sensor unit pixel of claim 7 , wherein the diffusion well remains floated while the light-receiving element operates.
9. The image sensor unit pixel of claim 7 , wherein the reset element of the unit pixel of an image sensor is connected to a diffusion layer in which a first-type of impurities are doped in high density on the diffusion well in which the first-type of impurities are doped.
10. An image sensor unit pixel, comprising:
a light-receiving element which generates an electric current by using change of electric charge quantity caused by incident light; and
a reset element which removes residual electric charges from the light-receiving element,
wherein the light-receiving element comprises:
a light-receiving unit which absorbs light;
an oxide film which contacts 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 the source and the drain, and the source and the drain facing each other;
a channel region formed between the source and the drain such that an electric current can be formed between the source and the drain; and
at least one wavelength expanding layer, formed in at least one among the light-receiving unit, the oxide film, and the channel region, and the at least one wavelength expanding layer split energy levels to form a plurality of local energy levels,
wherein the wavelength expanding layer is formed by applying stress onto an interface of a silicon layer and the oxide film.