Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935meV photoluminescence band occurs at intrinsic interstitial complexes, the 835meV band at small vacancy clusters, and the 1062meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835meV centers.

The evolution of vacancy-type defects has been studied by variable-energy positron annihilation spectroscopy (VEPAS) in samples of high-quality FZ p-type (001) silicon wafers implanted with 4 MeV Si2+ ions at room temperature to doses of 1012–1014 cm−2. The average vacancy concentration increases as (ion dose)0.70 ± 0.06. Progressive isochronal annealing measurements show that open-volume point defects (having a VEPAS signature close to that for divacancies) anneal between 500–600°C. VEPAS with enhanced depth sensitivity (via progressive etching) verified that single 30 min anneals to 550 and 600°C lead to the formation of buried clusters V N with an average N of 3.5 lying between depths of 2.2 and 3.6 μm (both ± 2 μm), close to the peak of vacancy damage just shallower than the ion range predicted by simulation. The concentration of these clusters increases as (ion dose)2.6 ± 0.1. Single anneals to higher temperatures reduce all open-volume point defect concentrations to below the limit detectable by VEPAS.

The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 1016 hadrons/cm2. Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed.

Si nanocrystals embedded in thermally grown SiO2 have been annealed at temperatures between 400 and 900 °C in a variety of atmospheres. Positron annihilation spectroscopy has been employed to study changes in the interface regions between nanocrystalline Si (nc-Si) and SiO2 with the support of photoluminescence measurements. We find that nitrogen and oxygen are trapped in the voids around nc-Si at low annealing temperatures. High-temperature annealing during the formation of nc-Si causes hydrogen originally residing in the SiO2/substrate region to enter the SiO2 structure. Hydrogen diffuse back to the SiO2/substrate region on annealing in vacuum at 400 °C because no other impurities block its diffusion channels. At annealing temperatures above 700 °C, both nitrogen and oxygen react with nc-Si, resulting in a volume increase. This introduces stress in the SiO2 matrix, which is relaxed by the shrinkage of its intrinsic open volume. The present data suggest that nitrogen suppresses Si diffusion in SiO2, so that the agglomeration of nc-Si is slower during annealing in nitrogen than in oxygen or vacuum.

We report data on high-quality silicon samples implanted with 4MeV silicon ions at doses of 1012–1014cm−2 measured using variable energy positron annihilation spectroscopy (VEPAS) and photoluminescence (PL). Individual, mainly interstitial related, defect centres can be observed with PL, and the average depth and concentration of vacancy clusters (assuming di-vacancies) can be found with VEPAS. We measure these samples as functions of dose and annealing from room temperature to 600°C and assess the circumstances in which PL can be used as a quantitative technique.

Positron annihilation spectroscopy has been employed to study changes in the interface region between nanocrystalline Si and SiO2, following annealing between 400°C and 900°C in nitrogen or oxygen. With the support of photoluminescence spectroscopy we find that nitrogen and oxygen are trapped in voids at the interface at low temperatures. At temperatures above 700°C both nitrogen and oxygen react with Si nanocrystals, and the resulting volume increase introduces stress in the SiO2 matrix which is relaxed by the shrinkage of its intrinsic open volume. Oxygen appears to enhance Si diffusion in SiO2 so that the agglomeration of Si nanocrystals occurs more readily during annealing in oxygen than in nitrogen.

The evolution with annealing of defects in self-ion implanted silicon with high carbon content has been investigated by photoluminescence (PL). The PL spectra show that the high-content carbon can effectively prevent the formation of {113} self-interstitial aggregates defect in silicon of implant dose 1013 and 1014cm−2 and largely suppress the formation of {113} defect at higher implant doses. By trapping and storing the excess interstitials a variety of stable carbon-related clusters are formed, which could persist to quite high annealing temperature. The strong asymmetry of the PL band near 910meV, with a long tail on the high-energy side, may originate from the size distribution of Ostwald ripening carbon-related clusters.

Photoluminescence enables a very large number of defects to be observed in ion-implanted silicon, over dose ranges of up to at least 1014cm−2. Simple arguments using the widths of the luminescence lines suggest that the defects lie in the heavily damaged part of the implanted crystal. We show that by combining optical absorption measurements on neutron-irradiated samples with luminescence measurements on implanted samples, the relative concentrations of ion-implantation defects may be determined. The luminescence spectra are shown to change considerably with temperature over the limited range 10–40 K. In this temperature range, the total number of photons emitted by the layer is conserved, further implying that the strengths of the signals from each defect are proportional to the concentrations of those defects. Some luminescence lines can be linked to DLTS signals, allowing the high resolution capabilities of luminescence to be combined with the ability of DLTS to measure concentrations, providing powerful joint probes into the properties of the implanted regions.