High-purity n-type silicon samples have been irradiated with mega-electron-volt ions ('H+, He'+, ' 0, "S'+, ' Br"+, and '"I'"+), and the two divacancy-related acceptor levels -0.23 and -0.42 eV below the conduction band (E,. ), respectively, have been studied in detail using deep-level transient spectroscopy (DLTS). Depth concentration profiles show identical values for the two levels at shallow depths, while in the region close to the damage peak large deviations from a one-toone proportionality are found. These deviations increase with ion dose and also hinge strongly on the density of energy deposited into elastic collisions per incoming ion. Evidence for a model of the two levels is presented and, in particular, the model invokes excited states caused by motional averaging and lattice strain associated with damaged regions. The divacancy center is known to exhibit a pronounced Jahn-Teller distortion at low temperatures (~20 K), and three equivalent electronic distortion directions exist. However, at higher temperatures ( 30 K) reorientation (bond switching) from one distortion direction to another takes place; in a perfect lattice the reorientation rate ultimately becomes so high that the defect does not relax in the distorted configurations, and a motionally averaged state with an effective point-group symmetry of D3d appears. At the temperatures where the DLTS peaks at E, -0.23 and E, -0.42 eV are observed, the reorientation time for bond switching is several orders of magnitude smaller than the time for electron emission from the two levels. This implies strongly that the levels originate from the motionally averaged state and not from the distorted state. Consequently, a clear distinction must be made between these DLTS peaks and the charge-state transitions observed in low-temperature studies where the divacancy is frozen in one of the three equivalent distorted configurations. Finally, the association of electronic energy levels with motionally averaged states is expected to apply not only for the divacancy but also for other defects where dynamic effects occur, e.g. , the monovacancy and the E center.

Deep energy levels caused by high-energy low-dose proton irradiation of both n- and p-type silicon have been investigated. Energy positions in the band gap, capture coefficients, and their temperature dependences for majority and minority carrier capture and entropy factors have been measured by deep level transient spectroscopy. Computer simulations have been employed to obtain the correct numbers of injected charge carriers needed for the evaluation of minority carrier capture data. From these measurements, it is possible to deduce the charge carrier lifetime profiles in proton irradiated n-type silicon for different injection concentrations and temperatures. At room temperature and for low injection, it is found that the singly negative divacancy level with a band-gap enthalpy of HC−HT=0.421 eV has the largest influence on the lifetime. At high injection, the vacancy–oxygen center, HC−HT=0.164 eV, is mostly responsible for the lifetime reduction.

Silicon samples of n-type have been implanted at room temperature with 5.6-MeV 28 Si ions to a dose of 2ϫ10 8 cm Ϫ2 and then annealed at temperatures from 100 to 380°C. Both isothermal and isochronal treatments were performed and the annealing kinetics of the prominent divacancy (V 2 ) and vacancy-oxygen ͑VO͒ centers were studied in detail using deep-level transient spectroscopy. The decrease of V 2 centers exhibits first-order kinetics in both Czochralski-grown ͑CZ͒ and float-zone ͑FZ͒ samples, and the data provide strong evidence for a process involving migration of V 2 and subsequent annihilation at trapping centers. The migration energy extracted for V 2 is ϳ1.3 eV and from the shape of the concentration versus depth profiles, an effective diffusion length р0.1 m is obtained. The VO center displays a more complex annealing behavior where interaction with mobile hydrogen ͑H͒ plays a key role through the formation of VOH and VOH 2 centers. Another contribution is migration of VO and trapping by interstitial oxygen atoms in the silicon lattice, giving rise to vacancy-dioxygen pairs. An activation energy of ϳ1.8 eV is deduced for the migration of VO, in close resemblance with results from previous studies using electron-irradiated samples. A model for the annealing of VO, involving only three reactions, is put forward and shown to yield a close quantitative agreement with the experimental data for both CZ and FZ samples over the whole temperature range studied.

4H-SiC epilayers were irradiated with either protons or electrons and electrically active defects were studied by means of deep level transient spectroscopy. Motion of defects has been found to occur at temperature as low as 350–400 K. Indeed, the application of an electric field has been found to enhance modifications in defect concentrations that can also occur during long time annealing at elevated temperature. Two levels have been revealed and labeled B and M. Two other levels, referred to as S1 and S2 and located at 0.40 and 0.71 eV below the conduction band edge have been studied in detail (capture cross sections, profiling, formation energy, activation energy during annealing). The S1 and S2 levels have been found to exhibit a one to one relation and are proposed to be two charge states of the same acceptor center, labeled the S center.

Damage accumulation in 4H–SiC under 1.1 MeV Al22+ irradiation is investigated as a function of dose at temperatures from 150 to 450 K. Based on Rutherford backscattering spectroscopy and nuclear reaction analysis channeling spectra, the damage accumulation on both the Si and C sublattices have been determined, and a disorder accumulation model has been fit to the data. The model fits indicate that defect-stimulated amorphization is the primary amorphization mechanism in SiC over the temperature range investigated. The temperature dependence of the cross section for defect-stimulated amorphization and the critical dose for amorphization indicate that two different dynamic recovery processes are present, which are attributed to short-range recombination and long-range migration of point defects below and above room temperature, respectively. As the irradiation temperature approaches the critical temperature for amorphization, cluster formation has an increasing effect on disorder accumulation, and ion flux plays an important role on the nature and evolution of disorder. Dislocation loops, which are mostly formed under high ion flux, act as sinks for point defects, thereby reducing the disorder accumulation rate.

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Thermochromic Mg-doped VO2 films were deposited by reactive direct current magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were inferred from Rutherford backscattering. Optical bandgaps were obtained from spectral transmittance and reflectance measurements—from both the film side and the back side of the samples—and ensuing determination of absorption coefficients. The bandgap of Mg-doped films was found to increase by 3.9 ± 0.5 eV per unit of atom ratio Mg/(Mg + V) for 0 < Mg/(Mg + V) < 0.21. The presence of ∼0.45 at. % Si enhanced the bandgap even more.

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