A transparent undoped bulk monocrystalline diamond is a new kind of important electro-optical crystal. Due to high resistivity the activation energies are hard to directly investigated by capacitance deep level transient spectroscopy (DLTS). Thus, three independent methods, isothermal transient spectroscopy (ITS), Current-DLTS and optical-excited DLTS (O-DLTS), were preformed to search defect information. Activation energies from 0.407 eV to 1.184 eV and capture cross section in the range from 10^-12 cm^-2 to 10^-18 cm^-2 have been obtained from ITS, current DLTS and O-DLTS. We found that more activation energies can be fitted from ITS than current DLTS and O-DLTS. The fitted activation energies from ITS are supported by current DLTS and Optical-DLTS, indicating ITS as a suitable technology for the high resistivity sample. Furthermore, the information of defect is useful for further development of photoelectric device based on diamond.

Deep level transient spectroscopy,Optical deep level transient spectroscopy,Isothermal transient spectroscopy,Diamond