Silicon drift detectors (SDDs) are X-ray radiation detectors used in x-ray spectrometry ( XRF and EDS) and

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

. Their chief characteristics compared with other X-ray detectors are: *high count rates *comparatively high energy resolution (e.g. 125 eV for Mn Kα wavelength) *

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Working principle

Like other solid state X-ray detectors, silicon drift detectors measure the energy of an incoming photon by the amount of ionization it produces in the detector material. This varying ionization produces varying charge, which the detector electronics measure for each incoming photon. In the SDD, this material is high purity silicon with a very low leakage current. The high purity allows for the use of

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cooling instead of the traditional liquid nitrogen. The major distinguishing feature of a SDD is the transversal field generated by a series of ring electrodes that causes charge carriers to 'drift' to a small collection electrode. The 'drift' concept of the SDD (which was imported from particle physics) allows significantly higher count rates coupled with a very low capacitance of the detector. In older detector designs, the collection electrode is centrally located with an external FET (

field effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...

) to convert the current into a voltage and thus represents the first stage of amplification. Newer designs integrate the FET directly into the chip, which greatly improves energy resolution and throughput. This is due to the reduction of capacitance between anode and FET, which reduces electronic noise. Other designs move the anode and FET outside of the irradiated area. This causes a slightly longer response time, which leads to a slightly lower throughput (750,000 counts per second instead of 1,000,000). However, due to the smaller anode size, this leads to better energy resolutions (down to 123 eV for Mn Kα wavelength). Combined with improved or adapted signal processing, it is possible to maintain the

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

drift detector's energy resolution up to 100,000 counts per second.Silicon Drift Detector development
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References

{{reflist Radiation X-ray instrumentation