Dember effect

Called the Dember effect, also photo - Dember effect or crystal photo effect, named after the physicist Harry Dember ( 1882-1943 ). It describes the formation of an electric voltage at the irradiation of light to a semiconductor.

Description

Physically the Dember effect is based on the following reason: When irradiating light sufficiently high energy (or a sufficiently short wavelength) of the semiconductor, electrons are raised from the valence band via the band gap of the semiconductor ( photo-electric effect). It created so-called electron -hole pairs (holes are missing electrons in the valence band of the semiconductor ). As the light is absorbed in the semiconductor, is the density of electron-hole pairs at the surface is highest, and is decreased in the semiconductor. This spatial decrease of the electron -hole pairs follows an exponential decay, the Lambert- Beer law. The gradient of the electron -hole pairs causes a diffusion current in the semiconductor. Now, electrons and holes are different heavy, they have different effective masses. In general, the effective mass of electrons is smaller than that of the holes, so electrons diffuse rapidly into the semiconductor. Characterized employs a spatial separation of electrons and holes. This spatial separation of electrons ( negative charges ) and holes ( positive charges ) generates an electrical voltage.

Application

The Dember effect also has relevance in the generation of the terahertz radiation from semiconductors. Where a short light pulse on a semiconductor, so the electrical voltage builds up by the Dember effect. When the light pulse is generated by a femtosecond laser, the structure of the voltage takes place in less than one picosecond. Through this process, electromagnetic radiation in the terahertz frequency range is emitted, which was first observed by Thomas Dekorsy.