Semiconductor detector

Under the influence of an electric field, electrons and holes travel to the electrodes, where they result in a pulse that can be measured in an outer circuit, as described by the Shockley-Ramo theorem.

Consequently, in semiconductor detectors the statistical variation of the pulse height is smaller and the energy resolution is higher.

The drawback is that silicon detectors are much more expensive than these older technologies and require sophisticated cooling to reduce leakage currents (noise source).

Before current purification techniques were refined, germanium crystals could not be produced with purity sufficient to enable their use as spectroscopy detectors.

The thickness of these contacts represents a dead layer around the surface of the crystal within which energy depositions do not result in detector signals.

The major drawback of germanium detectors is that they must be cooled to liquid nitrogen temperatures to produce spectroscopic data.

Germanium detectors with multi-strip electrodes, orthogonal on opposing faces, can indicate the 2-D location of the ionization trail within a large single crystal of Ge.

The high density of these materials means they can effectively attenuate X-rays and gamma-rays with energies of greater than 20 keV that traditional silicon-based sensors are unable to detect.

The wide band gap of these materials also means they have high resistivity and are able to operate at, or close to, room temperature (~295K) unlike germanium-based sensors.

These detector materials can be used to produce sensors with different electrode structures for imaging and high-resolution spectroscopy.

Efforts to mitigate this effect have included the development of novel electrodes to negate the need for both polarities of carriers to be collected.

Due to the complexities of opening the shield and moving the samples, this automation has traditionally been expensive, but lower-cost autosamplers have recently been introduced.