Strong impact of x-ray radiation associated with electron beam metallization of diamond devices

Electron-beam evaporation of metal contact is commonly used in the fabrication of semiconductor devices. We have observed that device irradiation by x-ray photons, which are generated by electrons striking the metal (titanium or gold) to be evaporated, has a strong impact on the characteristics of diamond devices used for radiation detection. It results in an improvement of the detector charge collection efficiency by a factor of 1.5 with respect to nonirradiated devices (standard thermal evaporation). Thermally stimulated current measurements showed that this effect is related to deep trap filling by free carriers generated in diamond by x-ray photons impinging the device during e-beam evaporation. Trap filling results in an increase of the free carrier drift distance before trapping. Study of contact annealing and the thermal stability of trap filling showed that charge detrapping at temperatures above 200 °C annihilates the observed detector sensitivity improvement.