photo effect

The photoelectric effect is a physical phenomenon first demonstrated by the French physicist Alexander-Edmond Becquerel in 1839. Later, this phenomenon was confirmed by the German physicists Heinrich Hertz and Wilhelm Hallwachs. Therefore, it is also called the Hallwachs effect.

The photoelectric effect is a photoelectric effect in which electrons are released from metallic surfaces when they are irradiated with light. When a surface is irradiated with light, photons strike it and tear electrons out of their compound. While Hallwachs still worked with zinc plates, later experiments used the semiconductor material selenium( Se), and still later germanium( Ge) and silicon( Si) were used. With this technology photocells, later photodiodes, phototransistors. Photo FETs and solar cells could be produced.

When semiconductors absorb light, they produce photons. If the energy of the photons is greater than the band gap of the semiconductor, they carry electrons through the incident light energy, from the energetically lower valence band across the band gap into the energetically higher conduction band. A certain amount of energy and the right wavelength are crucial for overcoming the band gap. In the valence band, they leave behind spurious electrons, i.e. positively charged electron holes. Between the conduction band and the valence band, an electron-feletelectron combination is formed. In silicon, the energy required for this, which is excited by light, is 1.26 eV. The incident light increases the electrical conductivity of the semiconductor. This is also referred to as photoconductivity. The higher the incident light intensity, the higher the conductivity.