Laser-induced novel ohmic contact formation for effective charge collection in diamond detectors

In this study, we employed an authentic process for the device fabrication of diamond detectors, wherein thin, highly conductive surface layers were processed in bulk diamond substrate using a nanosecond-pulsed excimer laser with liquid-immersion irradiation. The incorporation of high-concentration phosphorus dopants at 40 nm under the irradiated surface characterized the irradiated areas with much lower electrical resistivity, which was adequate for demonstrating ohmic contacts even with the tungsten probe heads at room temperature. In particular, a low activation energy (<54 meV) of irradiated surfaces enabled space-charge-free build-up effects between the diamond film and external connection. Moreover, the electrical characterization revealed an improved carrier-collection efficiency that was more than three orders of magnitude greater than that of typical Ti/Au diamond ohmic contacts, including a high-response speed of the current pulse to irradiation burst. The laser treatment of diamond films displayed promising results for the fabrication of diamond detectors with minimum power consumption, fastest process rate, and highest visible-light detection that could maintain smooth and stable charge transport. The process allowed selective, patterned doping of the diamond surface, which could be electrically contacted more readily. Furthermore, they could be operated at high temperatures and in radiation-harsh environments with sustainable efficiency.