Temperature evolution of photocurrent spectra in undoped and boron-doped homoepitaxial CVD diamond film

Photocurrent spectra in undoped and boron-doped homoepitaxial CVD diamond films were measured in the ultra-violet photon energy range 4 to 6 eV at different temperatures 250 to 450 K. A step-like structure starting at 4.6 eV was observed as a dominant structure on the spectra in both films. From the different temperature dependence of the step-like structure in between the undoped and boron-doped diamond films, it is suggested that the step-like structure is due to free holes generated by the optical transition of electrons from the valence band to localized absorption centers located at 0.8 to 0.9 eV below the bottom of the conduction band. The result of dual beam photocurrent measurement using a ultra-violet light and a He–Ne laser supports the existence of the absorption center near the conduction band.