Chemical vapor deposition(CVD)-grown diamond films have been developed as irradiation-resistant materials to replace or up-grade current detectors for use in extreme radiation environments.However,their sensitivity in practical applications has been inhibited by space charge stability issues caused by defects and impurities in pure diamond crystal materials.In this study,two high-quality CVD-grown single-crystal diamond(SCD)detectors with low content of nitrogen impurities were fabricated and characterized.The intrinsic properties of the SCD samples were characterized using Raman spectroscopy,stereomicroscopy,and X-ray diffraction with the rocking curve mode,cath-ode luminescence(CL),and infrared and ultraviolet-visible-near infrared spectroscopies.After packaging the detectors,the dark current and energy resolution under α particle irradiation were investigated.Dark currents of less than 5 pA at 100 V were obtained after annealing the electrodes,which is comparable with the optimal value previously reported.The detector that uses a diamond film with higher nitrogen content showed poor energy resolution,whereas the detector with more dislocations showed poor charge collection efficiency(CCE).This demon-strates that the nitrogen content in diamond has a significant effect on the energy resolution of detectors,while the dislocations in diamond largely contribute to the poor CCE of detectors.