Comparative study of natural and synthetic type IIa diamond detectors

Diamond has the highest radiation-damage level among radiation-detector semiconductor materials. Besides, low carbon nucleus charge, Z =6, provides tissue equivalence of diamond detectors. However, essential restrictions are imposed on production of natural-diamond detectors by extremely low final yield of selection procedure and corresponding expensiveness of high-quality type IIa natural diamonds. The solution of this problem could be found through the development of single-crystal synthetic-diamond detectors. Basic radiation-response properties of high-pressure high-temperature (HPHT) single-crystal synthetic-diamond (SD) detectors and natural-diamond (ND) detectors made of extremely low nitrogen content (type IIa) material were comparatively studied under hard X-ray, UV, and alpha-particle irradiation. Four orders of magnitude higher steady-state responsivity to radiation has been observed for SD detectors. The gain evaluated under UV irradiation exceeded 6000 (the corresponding value of responsivity was above 1000 A/W). The study of alpha-particle-induced electromotive force (EMF) polarity has revealed the opposite type of surface bending of energy bands in synthetic and natural diamonds. The difference in detector performance could be explained in terms of presented model of charge carrier injection and transport in diamond.