L. V. Krasilnikova

Optically active centers in Si/Si1 − x Ge x :Er heterostructures containing Er3+ ions

The basic types of optically active erbium centers that make the major contribution to the photo-luminescence signal from the Si/Si1 − xGex:Er heterostructures with the Ge content from 10 to 30% are analyzed in detail. It is shown that the origin of the optically active centers containing Er3+ ions correlates with the molar composition of the Si1 − xGex:Er layer and the content of oxygen impurity in the layer. The major contribution to the photoluminescence signal from the Si/Si1 − xGex:Er heterostructures with the Ge content below 25% is made by the well-known centers containing Er3+ ions and oxygen. An increase in the Ge content in the Si1 − xGex:Er layer (x ≥ 25%) yields the formation of a new type of centers, specifically, the Gecontaining optically active erbium centers unobserved in the Si-based structures previously.

Features of InN growth by nitrogen-plasma-assisted MBE at different ratios of fluxes of group-III and -V elements

The results of investigations of the effect of the ratios of fluxes of the Group-III and -V elements on the structural and optical properties of an InN film deposited by plasma-assisted molecular-beam epitaxy (MBE) are presented. It is shown that the InN layer consists of free-standing nanocolumns at a flux ratio of III/V < 0.6. InN growth becomes two-dimensional (2D) in the ratio range 0.6 < III/V < 0.9; however, the InN layer has a nanoporous structure. Upon passage to metal-rich conditions of growth (III/V ∼1.1), the InN layer becomes continuous. The passage from 3D to 2D growth is accompanied by an increase in the threading-dislocation density. It results in a decrease in the photoluminescence (PL) intensity of InN at room temperature. The electron concentration in the InN layers amounts to ∼5 × 1018 cm–3, which results in a shift of the PL-signal peak to the wavelength region of 1.73–1.8 μm and to a shift of the absorption edge to the region of ∼1.65 μm.

Specific features of the mechanisms of excitation of erbium photoluminescence in epitaxial Si:Er/Si structures

The excitation spectra and kinetics of erbium photoluminescence and silicon interband photoluminescence in Si:Er/Si structures under conditions of high-intensity pulse optical excitation are studied. It is shown that, in the interband photoluminescence spectra of the Si:Er/Si structures, both the luminescence of free excitons and the emission associated with the electron-hole plasma can be observed, depending on the excitation power and wavelength. It is found that the formation of a peak in the erbium photoluminescence excitation spectra at high pumping powers correlates with the Mott transition from the exciton gas to the electron-hole plasma. It is demonstrated that, in the Si:Er/Si structures, the characteristic rise times of erbium photoluminescence substantially depend on the concentration of charge carriers.

Erbium Doped Silicon Single- and Multilayer Structures for LED and Laser Applications

The paper is a brief retrospective review of our contribution to the Si:Er problem in the last decade. It contains a description of the experimental facilities, results of the light emitting media (Si:Er and Si1-xGex:Er) research and device applications. The progress in the development of Si:Er-based light-emitting devices with a higher power yield and quantum efficiency is associated with the improvement of the optically active media (increase of optically active Er 3+ concentration, formation of optically active Er-containing complexes with higher excitation cross-section and minimization of Er 3+ nonradiative relaxation processes) and optimization of the light emitting devices design. In this contribution we focus on both approaches: i) we report a new optically active Er-containing complex radiating at 1.54 µm, a novel mechanism of sub-band-gap photo-excitation of erbium in silicon; ii) show possibilities to enhance the power yield of electroluminescent light emitting devices (LEDs) including LEDs radiating at room temperature at reverse and forward bias of the p-n junction, demonstrate a novel long-term optical memory effect on the basis of Si:Er light emitting structure with the active Si:Er layer placed within the depletion region, discuss the perspectives and progress in the development of laser-type structures on Si:Er basis; iii) develop an original sublimation variant of the MBE technique (SMBE) and demonstrate its capabilities for realizing light-emitting devices effectively radiating up to room temperature. STRUCTURE GROWTH AND CHARACTERIZATION

Special features of the excitation spectra and kinetics of photoluminescence of the Si1 − xGex:Er/Si structures with relaxed heterolayers

Luminescent properties of heteroepitaxial Si1 − xGex:Er/Si structures with relaxed heterolayers are studied. The results of combined studies of the excitation spectra and kinetics of photoluminescence (PL) are used to single out the components providing the largest contribution to the PL signal of the Si1 − xGex:Er/Si structures in the wavelength region of 1.54 μm. It is shown that relaxation of elastic stresses in the Si1 − xGex:Er heterolayer affects only slightly the kinetic characteristics of erbium luminescence and manifests itself in insignificant contribution of the defects and defect-impurity complexes to the luminescent response of the Si1 − xGex:Er/Si structures. In the excitation spectra of the erbium PL, special features related to the possibility of the rare-earth impurity excitation at energies lower than the band gap of the Si1 − xGex solid solution are revealed. It is shown that a peak the width of which depends on the band gap of the solid solution and the extent of its relaxation is observed in the excitation spectra of the erbium-related PL in the Si1 − xGex:Er/Si structures in the wavelength region of 1040–1050 nm. The observed specific features are accounted for by involvement of intermediate levels in the band gap of the Si1 − xGex:Er solid solution in the process of excitation of an Er3+ ion.

Optically active Er3+ centers in Si/Si1 − xGex structures under optical pumping

The Si/Si1 − xGex:Er/Si heterostructures, which are of interest for laser applications, have been investigated. The types of optically active Er3+ centers making a dominant contribution to the photoluminescence response of the structures studied are analyzed and their relationship with the parameters of the Si1 − xGex:Er heterolayer and the post-growth annealing conditions is shown. On the basis of the PL kinetic analysis of the structures with an isolated type of optically active Er3+ centers, it is concluded that population inversion of Er3+ ion states can be obtained under optical pumping and the effect of nonradiative recombination channels in Si1 − xGex:Er heterolayers on the excitation efficiency of Er centers and the conditions for population inversion is shown.

Single- and multilayer Si:Er structures for LED and laser applications grown with sublimation MBE technique

We present here last results on development and research of Si:Er-based light emitting structures grown with original sublimation molecular beam epitaxy (SMBE) technique. The paper contains a description of the experimental facilities, results of the light emitting media (Si:Er and Si1-xGex:Er) research and device applications.