Development of layered type single crystalline diamond radiation detector as an energy spectrometer

Radiation detectors were fabricated with layered structure diamonds comprising several micrometers of a borondoped single crystal diamond and 20 μm of insulating single crystal diamond layers grown on a HP/HT-type Ib diamond single crystal substrate. To improve the yield rate of CVD diamond radiation detectors this approach was adopted. The detectors had rectification characteristics because of their boron-doped diamond contact and aluminum Schottky contact. The leakage current of one detector was less than 0.2 pA at reversed bias voltage of +50 V. Energy resolutions of 2.6% and 2.8% for alpha particles from ²⁴¹Am were achieved using these detectors. The rise time of a leading edge of an output signal from one detector was less than 20 ns, which was the fastest rise time of the measurement system; drift velocities of charge carriers were estimated to be faster than 1x10⁵ cm/s. In addition, cathode luminescence spectra of insulating diamond layers were measured; peaks caused by free exciton recombination and 'band A' were observed. Improved crystallinity of the boron-doped diamond layer helps realization of a layered-type diamond radiation detector with higher energy resolution. (author)