For semiconductor detectors, at least a pair of contacts are needed to supply high voltage and to collect the electrical signal resulted by interaction of radiation with the crystal and transportation of the charge toward anode and cathode. The method used to deposit contacts is called sputtering.
Sputtering is a cold evaporation technique which employs pure metals, alloys and compounds to deposit a layer of material onto a suitable substrate. We can use RF sputtering (instead of the more straight forward DC sputtering), because some of the materials are insulating materials.
Sputtering as a process to deposit thin films dates back to 1852 and has found limited use until 1928 when it was used for such applications as coating gold onto early phonograph cylinder masters.
Sputtering utilizes a gas plasma (argon, neon, krypton or xenon) to remove material from a negatively charged source called the target and to deposit it as a thin film coating onto asubstrate.
Magnets (magnetron) are placed under the target to constrain the secondary electrons from leaving the plasma volume before they have had a chance to ionize a gas atom. In this way the ionization rate in the plasma volume is increased. There are many process parameters which can influence the physical and chemical properties of the coating. For instance, the film composition depends on the target composition, the ionized gas pressure, the substrate temperature, and the energetic particle radiation (photons as well as other particles). For instance, in an RF discharge configuration, not only the electrons, but also positive ions, produced in the bulk plasma, are accelerated across the plasma and may arrive at the substrate with significant energies.