Positron-annihilationS-parameter measurements in thermal equilibrium on pure and carbon-doped (50 and 750 at. ppm) a-iron are presented. It is shown that trapping of positrons in both monovacancies and carbon-vacancy pairs occurs, even far above the dissociation temperature of the vacancy pairs. Therefore, a three-state trapping model is used in the analysis of the measured S curves. The vacancy-formation enthalpy in both the paramagnetic and ferromagnetic state is deduced: It is found to be 1.79%0.10 eV in the paramagnetic state and 2.0+0.2 eV in the ferromagnetic state. These values are larger than those published so far. The activation enthalpy for vacancy migration obtained by combining the values cited above with recently published self-diffusion enthalpy values confirms the applicability of the one-interstitial model in a-iron.

Characteristic features in photocurrent (PC) and electron paramagnetic resonance (EPR) spectra are discussed and attributed to main defects in the gap of optical-quality chemical vapor deposited diamond. A shoulder in the PC spectra with an onset at about 2.2 eV is attributed to the single-substitutional nitrogen defect (EPR P1 resonance at g=2.0024). A second feature in the PC spectra with an onset of about 1.3 eV is observed on “as-grown” samples with a hydrogen terminated surface. The defect level associated with this feature is hydrogen related, and this defect disappears after oxidation of the diamond sample surface. The EPR g=2.0028, which was also suggested to be H-related, is discussed.

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A spectroscopic study of epitaxial phosphorus-doped n-type diamond films, prepared by the chemical vapor deposition ͑CVD͒ technique, was carried out using the constant photocurrent method ͑CPM͒. Liquid nitrogen temperature CPM data show two new optically active defects in the gap of the P-doped CVD diamond film. A theoretical fitting of the optical cross-section data yields 0.56 eV optical excitation energy for the first level ͑denoted as X P1 ) and 0.81 eV for the second level ͑denoted as X P2 ). The X P1 optical data are in good agreement with Hall measurements, showing about the same value for the ͑thermal͒ activation energy of the carrier concentration for P-doped samples. The X P2 -defect level remains unidentified. Liquid helium temperature measurements for a high-electrical mobility n-type diamond sample show P-related oscillatory photoconductivity. ͓S0163-1829͑99͒02023-8͔