The effect of vacancies on the behavior of F in crystalline Si has been elucidated experimentally for the first time. With positron annihilation spectroscopy and secondary ion mass spectroscopy, we find that F retards recombination between vacancies (V) and interstitials (I) because V and I trap F to form complexes. F diffuses in the V-rich region via a vacancy mechanism with an activation energy of 2.12+/-0.08 eV. After a long annealing time at 700 degrees C, F precipitates have been observed by cross-section transmission electron microscopy which are developed from the V-type defects around the implantation range and the I-type defects at the end of range.

The TiO2∕SiO2 gate dielectric stack on 4H-SiC substrate has been studied as a high-κ gate dielectric for metal-oxide semiconductor devices. X-ray photoelectron spectroscopy confirmed the formation of stoichiometric TiO2 films. The leakage current through the stack layer was investigated and it has been shown to be a double conduction mechanism. At low fields, the current is governed by properties of the interfacial layer with a hopping like conduction mechanism, while at relatively high electric field, carriers are modulated by a trap assisted tunneling mechanism through traps located below the conduction band of TiO2. The current-voltage characteristics, time evolution of charge transport, and capacitance-voltage behaviors under constant voltage stressing suggest the composite effect of electron trapping and positive charge generation in the dielectric stack layer.

The photoluminescence intensity from ion-implanted silicon can be quenched by the radiation damage implicit in the implantation. Annealing is then required before the intensity of the luminescence from a defect center is approximately proportional to the concentration of that center. Data from positron annihilation and photoluminescence experiments establish that severe quenching of the luminescence occurs when the mean separation of the small vacancy clusters is less than ϳ30 atomic spacings, and the authors map out where, in the annealing and implantation phase space, the luminescence intensity is expected to be approximately proportional to the concentration of the optical centers.

Mean concentrations CD of aggregated vacancy-type point-defect structures in float-zone Si implanted with H+, B+, Si+, O+, and Ge2+ ions at energies between 0.45 and 4.0 MeV have been measured as a function of ion dose φ at depths ∼RP/2 (half projected ion range) by beam-based positron spectroscopy. By adjusting φ to φA using factors given by the code TRIM, one arrives at the universal expression CD=(2.79×1010) φA0.63; CD (cm−3) can be estimated to ±50% for MeV ions implanted for φA from 109×1013 cm−2, which corresponds to an upper limit dose approaching 1014 cm−2 for 2 MeV Si+ implantation.

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