The optical properties of luminescence centres in silicon

Persistent efforts have been made to achieve efficient light emission from silicon1,2,3,4,5,6,7 in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects8. Enhanced light emission from silicon is known to be theoretically possible9,10, enabled mostly through quantum-confinement effects2,3,4. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides11,12. Here we report on optical gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask13. In edge-emission measurements, we observed threshold behaviour, optical gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission14,15,16,17. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes18,19,20. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured optical gain and stimulated emission and provides a new pathway to enhance light emission from silicon.

Optical gain and stimulated emission in periodic nanopatterned crystalline silicon.

Scanning force microscopy is extended by the pulsed force mode from simple imaging of topography to measuring elastic, electrostatic and adhesive sample properties. Lateral forces are virtually eliminated so that mapping of delicate samples with high resolution in air and fluids is easily possible. Scanning speed is comparable to that in contact mode. The new opportunities for scanning force microscopy given by the pulsed force mode is demonstrated in selected applications.

Pulsed force mode: a new method for the investigation of surface properties

An electron paramagnetic resonance spectrum, observed in electron irradiated silicon and labeled Si‐G15, is shown to originate from the same carbon‐oxygen complex as does the well studied C‐line photoluminescence spectrum with zero‐phonon line at 0.79 eV. Both the g tensor and the 13C hyperfine tensor for this center are remarkably similar to those for the isolated interstitial carbon atom. Stress‐induced alignment experiments reveal the role of oxygen and indicate a unique structure for an interstitial carbon‐interstitial oxygen pair.

Identification of an interstitial carbon‐interstitial oxygen complex in silicon

This review article describes progress made in scanning force microscopy of polymers during the last 5 years including fundamental principles of SFM and recent developments in instrumentation relevant to polymer systems. It focuses on the analytical capabilities of SFM techniques in areas of research where they give the most unique and valuable information not accessible by other methods. These include (i) quantitative characterisation of material properties and structure manipulation on the nanometer scale, and (ii) visualisation and probing of single macromolecules.

Imaging of Polymers Using Scanning Force Microscopy: From Superstructures to Individual Molecules

Low-temperature photoluminescence spectra are presented for Si crystals which have been irradiated with high-energy electrons. Studies of isochronal annealing, stress effects, and the temperature dependences of the luminescence are used to discuss the nature of the luminescent transitions and the properties of defects. Two dominant bands present after room-temperature anneal of irradiated material are discussed, and correlations of the properties of these bands are made with known Si defects. A band between 0.8 and 1.0 eV has properties which are related to those of the divacancy, and a band between 0.6 and 0.8 eV has properties related to those of the Si-G15(K) center. Additional peaks appear in the luminescence after high-temperature anneal; the influence of impurities and the effects of annealing of these lines are discussed.

Temperature, stress, and annealing effects on the luminescence from electron-irradiated silicon

Lithium doping has a dramatic effect on the low-temperature photoluminescence of electron-irradiated Si. In oxigen-lean Si with Li doping, a new irradiation-dependent luminescence band between 0.75 and 1.05 eV is observed, which is dominated by a zero-phonon peak at 1.045 eV. This band is believed to be due to radiative transitions involving a Li-modified divacancy. This band is present also in oxygen-rich, Li-diffused Si and is accompanied by bands previously related to the Si-G15(K) center and the divacancy. The intensities of the Li-modified divacancy and Si-G15(K) center bands are relatively weak in the oxygen-rich material, apparently due to the formation of lithium-oxygen complexes which reduce the concentration of unassociated interstitial Li and O.

Recombination luminescence from electron‐irradiated Li‐diffused Si

Current oscillations similar to those previously reported in various semiconductors with impurity‐induced traps have been observed in Si irradiated at 0°C with 1‐MeV electrons. The oscillations are altered by annealing of the devices at temperatures below 0°C.

CURRENT OSCILLATIONS IN Si p‐i‐n DEVICES AFTER IRRADIATION WITH ONE‐MeV ELECTRONS

Recent experimental and analytical results indicate that the 0.97‐eV luminescence from irradiated Si is characterized by monoclinic symmetry. The assignment of symmetry class for other luminescence peaks in this material is incomplete.

B. G. Streetman

Papers

Temperature, stress, and annealing effects on the luminescence from electron-irradiated silicon

Recombination luminescence from electron‐irradiated Li‐diffused Si

CURRENT OSCILLATIONS IN Si p‐i‐n DEVICES AFTER IRRADIATION WITH ONE‐MeV ELECTRONS

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