Dosimetric Control with Diode

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A diode is an internal boundary between p-type and n-type region in a single crystal. At the transition from p- to n-type material, a charge free depletion layer is formed, when an electrostatic difference is created (for silicon diode it is about 0.7 V). When the diode is irradiated, an electron-hole pair may be created in the depletion layer. The p- and n- sides of the junction attract the electrons and holes, respectively. Depending on the relative concentration of the acceptor impurities and the donor atoms a diode can be a p or n type diode. For p type diode the donor atoms are in higher concentration, lot of recombination centres are present, which leads to a high probability of recombination for the holes. When connecting the both side, a current will be detected at radiation, which, when the diode is unbiased, is proportional to the number of electron-hole pairs produced, which is proportional to the dose.
Advantages of diodes: real time readout, high sensitivity, good special resolution, air pressure independence. In clinical practice a special type of diode is used. For external photon beam dosimetry the diodes need a build-up material depending on the energy range for which a detector was intended.