EVIDENCE FOR THE PRINCIPAL DEFECT STATES IN CVD DIAMOND FILMS - OPTICAL STUDY

Photothermal deflection spectroscopy (PDS) was used to study the subga p optical absorption in CVD diamond films. All films exhibited a very characteristic shape of the absorption in the IR and visible spectral regions, varying in intensity over several orders of magnitude and dep ending on the film quality. The study of the morphology proved that th e films with the highest subgap absorption were nanocrystalline with i ncreased surface area of grain boundaries. The optical absorption spec tra of these films resembled the optical absorption in amorphous carbo n films which is due to the optical transitions in the pi-pi pseudoga p. The best quality CVD diamond attained the character of the fundamen tal indirect absorption edge of diamond with strongly reduced characte ristic subgap absorption. From secondary ion mass spectrometry analysi s it is shown that the characteristic absorption cannot be due to the extrinsic impurities.