The Basic Idea of the Photoelectric Effect

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Modern Digital Sensors use two main types of systems; CCD (charge-coupled device) and CMOS APS (complementary metal oxide semiconductor active pixel sensor). Light is made of photons. A photon is an indivisible particle of light.
The basic idea of the Photoelectric effect is the observation that electrons are emitted from energy levels when hit with enough energy from a photon. In this context, photons hit electrons found inside the sensor, and with enough energy escapes into the conduction band, which is a higher energy level. This process is referred to as scattering. The electrons found in the capacitor are the ones that were found in the conduction band and the depletion region.
This process occurs inside a semiconductor that is found inside the sensor. A semiconductor contains two bands: a valence band and conduction band. The valence band does not allow electrons to move at all whereas, when in the conduction band, electrons can move around in their energy levels. This is because the valence band contains energy levels that are compact inside the lattice of the atom, whereas c...

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