Microelectronic image sensors used in digital cameras such as CCD and CMOS generation of electrons authorization of photons to detect the incident light. We want to give a deeper insight into the physics of this phenomenon.

Photons rec Collide Image Sensor

Provided that the incident photons can break the covalent bonds holding electrons on atomic sites of the network, as the photon energy is sufficient. This is what happens when you press the shutter buttonour camera. The light from the scene that we shot hits the image sensor. Image sensors are made of silicon, like other integrated circuits. Once the covalent bond has been broken, the electrons freed in a position to move in semi-conductors. This process is called "Photo-generation." As for the band structure energy, which corresponds to electrons excited from the valence band to the conduction band.

Sensors respond to infrared radiation

ForPhoton to be able to do so, he must have power equal to or greater than the bandgap energy is the energy between the valence band and conduction. The Gap Band in silicon with no applied voltage and temperature is 1.124eV. This is the most visible part of the electromagnetic spectrum at a wavelength of 1.10 microns. So now we know that digital camera sensors are sensitive to infrared radiation. As a photographerusually do not want to enter into this part of the spectrum, a goal it is necessary to filter the infrared rays before the light reaches the sensor. All cameras are equipped with such filters. Digital cameras allow infrared photography, but have the ability to remove the internal filter.

Absorption coefficient

The incident radiation is absorbed on the surface of semiconductors as it enters the crystal lattice. The equation that describes this processis

I (x) = I exp (-ax)

where "I" is the energy that reaches the surface of the semiconductor (sensor), "x" is the depth in the semiconductor and "a" is a coefficient, the coefficient of absorption. "Since the exponential always says, the absorption is very strong, so that the photons are easily absorbed, as the sensor on. Absorption coefficient is a strongly decreasing function of the wavelength of photons. To give a magnitude, high-energy UV –Radiation penetrates about 10 nm in silicon before dissipating significantly, while the infrared light of about 100 microns, or 10,000 times smaller. The absorption of photons with energy above The Gap Band almost exclusively on the production of electrons.

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