SUBGAP OPTICAL-ABSORPTION IN CVD DIAMOND FILMS DETERMINED FROM PHOTOTHERMAL DEFLECTION SPECTROSCOPY

Photothermal deflection spectroscopy (PDS) was applied for the first t ime to measure the subgap optical absorption, induced by defects in fr ee-standing diamond films. Compared with the optical transmission meas urement, PDS is far more sensitive and even a defect concentration bel ow parts per million level can be identified. Moreover, the elastic li ght scattering influences the measured data significantly less. The op tical absorption measurement shows an optical transition which starts at about 1 eV, independently of the sp(2) content in the film. This le vel agrees well with the 1 eV activation energy of the dark conductivi ty. Additionally, an optical transition starting at about 3 eV is obse rved for white colourless films.