Rolandas Tomasiunas

Stimulated emission in blue-emitting Si+-implanted SiO2 films?

We investigate the blue photoluminescence of Si+-implanted SiO2 films under picosecond UV excitation. The emission intensity exhibits a nonlinear increase with increasing excitation intensities, accompanied by pulse shortening. The photoluminescence decays nonmonoexponentially in time. However, the nonlinearities are not associated with significant spectral narrowing. To explain the results, we propose and numerically investigate a kinetic model based on competition between radiative (both spontaneous and stimulated) and nonradiative recombination in isolated luminescence centers in the SiO2 matrix. Good agreement between theoretical and experimental data seems to confirm the existence of stimulated emission in the films, however, under extremely high excitation densities only (approximately 100 MW/cm2).

Active planar optical waveguide made from luminescent silicon nanocrystals

We show experimentally that a layer of silicon nanocrystals, prepared by the Si-ion implantation (with the energy of 400 keV) into a synthetic silica slab and exhibiting room-temperature red photol ...

Studies of silicon nanocrystals in phosphorus rich SiO2 matrices

Abstract In this contribution we present a new type of optoelectronic silicon nanocrystal (Si-nc) based material, namely, Si-nc embedded into solidified pure or doped spin-on-glasses. The resulting self-supporting samples contain thin layers with high Si-nc concentrations. The visible photoluminescence (PL) maximum at room temperature is blue-shifted when the concentration of phosphorus in the spin-on-glass is increased.

Replication technology for photonic band gap applications

Abstract Replication technology was applied for photonic structure fabrication in silicon substrate. It was revealed, that thin thermoplastic polymer layers on silicon substrates may be patterned by hot embossing technique for dry etching masking. Ni mold used for plain hot embossing into polymer layers was fabricated by Ni electrochemical deposition on the reference silicon surface structure, which was obtained by direct electron beam (EB) writing and SF 6 /N 2 reactive ion etching (RIE) technique. It is shown that the shape of replicated photonic structures is determined by RIE parameters.

Monolithic integration of rare-earth oxides and semiconductors for on-silicon technology

Several concepts of integration of the epitaxial rare-earth oxides into the emerging advanced semiconductor on silicon technology are presented. Germanium grows epitaxially on gadolinium oxide despite lattice mismatch of more than 4%. Additionally, polymorphism of some of the rare-earth oxides allows engineering of their crystal structure from hexagonal to cubic and formation of buffer layers that can be used for growth of germanium on a lattice matched oxide layer. Molecular beam epitaxy and metal organic chemical vapor deposition of gallium nitride on the rare-earth oxide buffer layers on silicon is discussed.

alpha-C:H films for photonic structure fabrication

(alpha) -C:H films were applied to fabricate photonic band gap (PBG) structures in the silicon substrate by SF6N2-based reactive ion etching (RIE). The influence of RIE parameters on (alpha) C:H films structure and etching rate was investigated int his study. It is shown that RIE rate for (alpha) -C:H films changes from 26 nm/min to 38 nm/min with the integrated intensity ratios ID/IG varied from 0.65 to 1.1. It is evident that increase in etching rate is determined by increasing quantity of sp2 bonding in the synthesized (alpha) -C:H films. RIE does not change structure of the (alpha) -C:H masking films. However, non- uniform character of RIE takes place due to the non- homogeneous graphite clusters in (alpha) -C:H masking films. However, non-uniform character of RIE takes place due to the non-homogeneous graphite clusters in (alpha) -C:H masking films. By changing parameters of silicon etching, such as RF power density, pressure and negative bias voltage, anisotropy was varied in wide range and microstructures of different shape were obtained.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Submicrometer lithography by near-field optical microscopy

Optimization of (i) intensity of illumination and (ii) thickness of resist was made looking for the conditions when high spatial resolution could be achieved by optical near- field lithography. Standard set-up of near-field illumination through a tapered Al-coated fiber tip was employed for the exposure of positive resist OFPR-5000 (EG), which is photo-sensitive for wavelength (lambda) 10 nm).© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Silicon-based light-emitting materials: implanted SiO2 films and wide-bandgap a-Si:H

We review critically recent results of investigation of hydrogenated amorphous silicon (a-Si:H) and Si+- implanted SiO2 films from the point of view of light- emission applications. Wide bandgap a-Si:H with the energy gap ranging from 2.0 to 2.2 eV exhibits room temperature photoluminescence in the visible region. Electroluminescence, however, occurs after previous recrystallization of a-Si:H only and seems not to be perspective for large scale applications. Si+-implanted SiO2 films contain, after proper annealing at 1000 - 1100 degrees Celsius, Si nanocrystals that luminesce in the red. In parallel another emission band can occur (in the blue region) which is related to post-implantation defects. We demonstrate that in SiO2 films homogeneously implanted across the entire film thickness red electroluminescence can be easily observed, presumably due to injection of electron-hole pairs into Si nanocrystals. Finally, the present status of prospects of stimulated emission achievement in low-dimensional Si structures is briefly summarized.