Electrical characterization of majority carrier traps in electron irradiated epitaxial N-type Si

Epitaxial p+/n–/n+ silicon diodes have been irradiated with 6 MeV electrons to a dose of 1014 cm−2, and isochronal and isothermal annealings at the temperatures 325 – 360 C has been performed. The reaction kinetics of VO, V2O and VOH is studied and compared to the corresponding defect behavior in diffusion oxygenated float zone (DOFZ) and magnetic Czochralski (MCz). VO and V2O is found to mainly dissociate, in correspondance with studies in DOFZ and MCz, but a fraction of VO also anneals by production of VOH as found by depth profiling. Depth profiling also suggests that VOH subsequently disappears through the generation of VOH2. Modeling is performed which confirms these conclusions. The growth rate of VOH, with c0 = 3 × 1013 s−1, is further argued to be close to the dissociation rate of a near–surface hydrogen complex HZ because of the high diffusivity of H. Furthermore, the loss of an unidentified defect labeled E(170 K) is proportional to the growth of VOH, and the ratio approaches unity at 360 C. Ea and c0 is also identical for the decay of E(170 K) and the growth of VOH. Thus, the decay of E(170 K) is believed to be because of the reaction E(170 K) + Z ! inactive complex, where the diffusivity of Z is large. The growth of a second unidentified defect labeled E(198 K) is proportional to the loss of V2O, with a ratio of 0.14 ± 0.03

Oxidation-enhanced annealing of implantation-induced Z(1/2) centers in 4H-SiC: Reaction kinetics and modeling

High-purity epitaxial layers of n-type 4H-SiC have been implanted with 4.3-MeV Si ions to a dose of 3 × 108 cm−2 and then subjected to dry isothermal oxidation at temperatures between 1050 and 1175 °C. Analysis of the samples by depth-resolved deep level transient spectroscopy unveils a strong oxidation-enhanced annealing of the prominent Z1/2 center, commonly ascribed to the carbon vacancy. The integrated (total) loss of Z1/2 centers is proportional to the thickness of the silicon dioxide (SiO2) layer grown but the proportionality constant, or annihilation efficiency, decreases with decreasing oxidation temperature. At a given depth x, the annealing of Z1/2 obeys first-order kinetics with a rate constant c having an activation energy of ∼5.3 eV. The pre-exponential factor c decreases with increasing x and a normalized concentration-versus-depth distribution of the species injected from the surface and annihilating the Z1/2 centers has been deducted. This species is believed to be the carbon interstitial and is labeled CI: numerical simulations of the reaction kinetics employing a model where (i) the generation rate of CI at the SiO2/SiC interface is related to the oxidation rate, (ii) the diffusion of CI into the SiC layer is fast, and (iii) a steady-state concentration profile of CI is rapidly established, yield good agreement with the experimental data for the evolution of both Z1/2 (absolute values) and CI (relative values) with temperature, depth, and time. The activation energy obtained for the diffusivity of CI is ∼3.0 eV, presumably reflecting the migration barrier for CI and possibly some contribution from an extra barrier to be surmounted at the SiO2/SiC interface. © 2012 American Physical Societ

Long range lateral migration of intrinsic point defects in n-type 4H-SiC

The lateral distributions of intrinsic point defects in n-type (0001) 4H-SiC have been investigated following room temperature irradiation with a focused beam of 10 keV protons. Laterally resolved deep level transient spectroscopy measurements reveal that the well-known and prominent Z1/2 and S1/2 centers display lateral diffusion lenghts on the order of 1 mm with negligible (if any) motion parallel to the direction of the c-axis. The migration occurs only in the presence of excess charge carriers generated during the proton irradiation, and no further motion takes place even under subsequent optical excitation of high intensity. Assuming one-dimensional geometry, an effective defect diffusivity in excess of 10−6 cm2/s is deduced by numerical modelling of the experimental data, corresponding to an energy barrier for migration of ∼0.2 eV. Possible mechanisms for the rapid migration, invoking charge carrier recombination as a necessary condition, are discussed, and especially, an association with the glide of partial dislocations along the (0001) basal plane is scrutinized in some detail. This research was originally published in the Journal of Applied Physics. © AIP Publishin

RD50 Status Report 2008 - Radiation hard semiconductor devices for very high luminosity colliders

The objective of the CERN RD50 Collaboration is the development of radiation hard semiconductor detectors for very high luminosity colliders, particularly to face the requirements of a possible upgrade scenario of the LHC.This document reports the status of research and main results obtained after the sixth year of activity of the collaboration