Optical and microstructural properties of self-assembled InAs quantum structures in silicon

The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm^?1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs.     

Reactivation of damaged rare earth luminescence centers in ion-implanted metal–oxide–silicon light emitting devices

Charge trapping and quenching of electroluminescence (EL) in SiO₂ layers implanted by Ge and rare earth (RE) ions during hot electron injection were investigated. In case of the SiO₂:Ge layer the EL quenching is caused by the transformation of the luminescent defects (Ge–Si or Ge–Ge) to optically inactive centers during hot electron excitation, whereas the EL from rare earth centers is quenched due to the electron trapping by RE-centers or their surroundings, but not due to their optical deactivation. Therefore, the flash lamp post-injection annealing releasing trapped electrons reactivates RE centers and increases the operating time of metal–oxide–silicon light emitting devices (MOSLEDs). PACS 72.20.Jv; 73.40.Qv; 73.50.Gr     

The effect of annealing under hydrostatic pressure on the visible photoluminescence from si-ion implanted SiO2 films

We have studied the influence of the hydrostatic pressure during annealing on the intensity of the visible photoluminescence (PL) from thermally grown SiO₂ films irradiated with Si⁺ ions. Post-implantation anneals have been carried out in an Ar ambient at temperatures T_a of 400°C and 450°C for 10 h and 1130°C for 5 h at hydrostatic pressures of 1 bar–15 kbar. It has been found that the intensity of the 360, 460 and 600 nm PL peaks increases with rising hydrostatic pressure during low-temperature annealing. The intensity of the short-wavelength PL under conditions of hydrostatic pressure continues to rise even at T_a=1130°C. Increasing T_a leads to a shift in the PL spectra towards the ultraviolet range. The results obtained have been interpreted in terms of enhanced, pressure-mediated formation of ≡Si–Si≡ centres and small Si clusters within metastable regions of the ion-implanted SiO₂.     

Silicon-on-insulator microcavity light emitting diodes with two Si/SiO2 Bragg reflectors

Light emitting pn-diodes were fabricated on a 5.8 μm thick n-type Si device layer of a silicon-on-insulator (SOI) wafer using standard silicon technology and boron implantation. The thickness of the Si device layer was reduced to 1.3 μm, corresponding to a 4λ-cavity for λ=1150 nm light. Electroluminescence spectra of these low Q-factor microcavities are presented. Addition of Si/SiO₂ Bragg reflectors on the top and bottom of the device (3.5 and 5.5 pairs, respectively) is predicted to lead to spectral emission enhancement by ∼270.     

Detection and Visualization Methods Used in Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - The use of thin-layer chromatography (TLC) for separation, identification and quantification of different organic and inorganic...     

Formation of InAs quantum dots in silicon by sequential ion implantation and flash lamp annealing

InAs quantum dots (QDs) were successfully formed in single-crystalline Si by sequential ion implantation and subsequent milliseconds range flash lamp annealing (FLA). Samples were characterized by μ-Raman spectroscopy, Rutherford Backscattering Spectrometry (RBS) high-resolution transmission electron microscopy (HRTEM) and low temperature photoluminescence (PL). The Raman spectrum shows two peaks at 215 and 235 cm^?1 corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs phonon modes, respectively. The PL band at around 1.3 μm originates from the InAs QDs with an average diameter 7.5±0.5 nm and corresponds to the increased band gap energy due to the strong quantum confinement size effect. The FLA of 20 ms is sufficient for InAs QDs formation. It also prevents the out-diffusion of implanted elements. Moreover, the silicon layer amorphized during ion implantation is recrystallized by solid-phase epitaxial regrowth during FLA.     

Physical limitations of the electroluminescence mechanism in terbium-based light emitters: matrix and layer thickness dependence

The physical limits of downscaling the SiO₂ thickness of rare earth implanted metal–oxynitride–oxide–semiconductor-based light emitters are explored by investigating the drop down of the electroluminescence power efficiency with decreasing SiO₂ thickness of Tb-implanted devices. It will be experimentally shown that there is a dark zone with an extension of about 20 nm behind the injecting interface in which the hot electrons have not yet gained enough kinetic energy in order to excite the Tb³⁺ luminescence centers. In addition, replacing the host matrix SiO₂ by SiON results in a decrease of power efficiency by two orders of magnitude what is consistent with the experimental data about the hot energy distribution in these media.     

Characterization of a SiC/SiC composite by X-ray diffraction, atomic force microscopy and positron spectroscopies

A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy and various positron spectroscopies (slow positron implantation, positron lifetime and re-emission). It is found that besides its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented.     

Correlation between defect-related electroluminescence and charge trapping in Gd-implanted SiO<Subscript>2</Subscript> layers

When amorphous silica is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (oxygen deficient centers (ODC), non-bridging oxygen hole centers (NBOHC), E^′-centers, etc.). Luminescent peaks from oxygen deficiency centers at 2.7 eV, non-bridging oxygen hole centers at 1.9 eV and defect centers with emission at 2.07 eV were observed by changing the concentration of implanted Gd³⁺ ions. Charge trapping in Gd-implanted SiO₂ layers was induced using constant current electron injection to study the electroluminescence intensity with dependence on the applied voltage change. The process of electron trap generation during high field carrier injection results in an increase of the electroluminescence from non-bridging oxygen hole centers. Direct correlation between electron trapping and the quenching of the electroluminescence at 2.07 eV and 2.7 eV was observed with variation of the implanted Gd concentration. PACS 78.60.i; 72.20.Jv; 78.20.-e     

Light-emitting silicon <Emphasis Type="Italic">pn</Emphasis> diodes

We report on the electrical and optical characteristics of silicon light-emitting pn diodes. The diodes are prepared by ion implantation of boron at high doses and subsequent high-temperature annealing. Under forward bias, the diodes emit infrared electroluminescence closely below the band gap of bulk Si. We present a rate-equation model for bound excitons, free excitons and free carriers which successfully describes the electrical and optical behaviour of the diodes at low temperatures. Especially, an electrical bistability observed below 50 K is shown to be based on the interplay of bound excitons, free excitons and free carriers in the active area of the diodes. The ionisation of bound excitons is the origin of an improved electroluminescence from the diodes at higher lattice temperatures. PACS 78.60.Fi; 78.55.Ap; 71.35.-y; 71.55.Cn