Special features of the excitation spectra and kinetics of photoluminescence of the Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:Er/Si structures with relaxed heterolayers

Luminescent properties of heteroepitaxial Si_{1 − x} Ge _x :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 Si_{1 − x} Ge _x :Er/Si structures in the wavelength region of 1.54 μm. It is shown that relaxation of elastic stresses in the Si_{1 − x} Ge _x :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 Si_{1 − x} Ge _x :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 Si_{1 − x} Ge _x 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 Si_{1 − x} Ge _x :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 Si_{1 − x} Ge _x :Er solid solution in the process of excitation of an Er³⁺ ion.     

Erbium Segregation in Silicon Layers Grown by Molecular-Beam Epitaxy

In the course of molecular-beam epitaxy of Er-doped Si on Si(100) substrates at 450–650°C, the dopant tends to segregate in the surface layer at doping levels from 10¹⁷ to above 10¹⁹ cm^–3. The introduction of oxygen into the growing epilayer—either from the gas phase at an oxygen pressure of 6.7 × 10^–6 Pa or from an SiO₂ layer on the substrate surface—suppresses the surface segregation of Er.     

Terbium photoluminescence in yttrium aluminum garnet xerogels

Based on a colloidal solution containing terbium, yttrium, and aluminum metal ions, a powder was synthesized and films of terbium-doped yttrium aluminum garnet Tb_0.15Y_2.85Al₅O₁₂ were grown on single-crystal silicon and porous anodic alumina. Annealing of the sample in a temperature range from 200–1100°C results in an increase in the photoluminescence intensity in the wavelength range from 480–640 nm, which is caused by Tb³⁺ ion intra-atomic transitions ⁵ D ₄→⁷ F _j (j = 3, 4, 5, 6). Annealing at 900°C and higher temperatures gives rise to low-intensity photoluminescence bands in the region of 667 and 681 nm, which correspond to transitions ⁵ D ₄→⁷ F ₀, ⁵ D ₄→⁷ F ₁, and room-temperature Stark term splitting, which suggests the existence of a crystalline environment of Tb³⁺ ions. The FWHM of spectral lines in the region of 543 nm decreases from ～10 to ～(2–3) nm as the xerogel annealing temperature is increased from 700 to 900°C and higher. Three bands with maxima at 280, 330, and 376 nm, which correspond to Tb³⁺ ion transitions ⁷ F ₆→⁵ I ₈, ⁵ L ₆, ⁵ G ₆, ⁵ D ₃, are observed in the photoluminescence excitation spectra of the studied structures for the emission wavelength at 543 nm. X-ray diffraction detected the formation of a crystalline phase for a terbium-doped yttrium aluminum garnet powder after annealing at 1100°C.     

Luminescence of Spatially Ordered Self-Assembled Solitary Ge(Si) Nanoislands and their Groups Incorporated into Photonic Crystals

Semiconductors - The luminescence properties of arrays of spatially ordered self-assembled solitary Ge(Si) nanoislands and their groups, including those embedded in two-dimensional photonic...     

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×10¹⁸ and 4×10¹⁹ cm⁻³, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm²/(V·s). Intense photoluminescence at 1.537 μm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown. Fiz. Tekh. Poluprovodn. 33, 156–160 (February 1999)     

Low-temperature growth of silicon epitaxial layers codoped with erbium and oxygen atoms

The fabrication technology and properties of light-emitting Si structures codoped with erbium and oxygen are reported. The layers are deposited onto (100) Si by molecular beam epitaxy (MBE) using an Er-doped silicon sublimation source. The partial pressure of the oxygen-containing gases in the growth chamber of the MBE facility before layer growth is lower than 5 × 10^?10 Torr. The oxygen and erbium concentrations in the Si layers grown at 450°C is ～1 × 10¹⁹ and 10¹⁸ cm^?3, respectively. The silicon epitaxial layers codoped with erbium and oxygen have high crystal quality and yield effective photoluminescence and electroluminescence signals with the dominant optically active Er-1 center forming upon postgrowth annealing at a temperature of 800°C.     

Multilayer photosensitive structures based on porous silicon and rare-earth-element compounds: Study of spectral characteristics

The spectral characteristics of the specular reflectance, photosensitivity, and photoluminescence (PL) of multilayer structures based on porous silicon with rare-earth-element (REE) ions are investigated. It is shown that the photosensitivity of these structures in the wavelength range of 0.4–1.0 μm is higher than in structures free of REEs. The structures with Er³⁺ ions exhibit a luminescence response at room temperature in the spectral range from 1.1 to 1.7 μm. The PL spectrum of the erbium impurity is characterized by a fine line structure, which is determined by the splitting of the ⁴ I _15/2 multiplet of the Er³⁺ ion. It is shown that the structures with a porous layer on the working surface have a much lower reflectance in the entire spectral range under study (0.2–1.0 μm).     

Simultaneous doping of silicon layers with erbium and oxygen in the course of molecular-beam epitaxy

Epitaxial silicon layers codoped with erbium and oxygen were grown by molecular-beam epitaxy using a silicon sublimation source. For growing the erbium-doped silicon layers, two types of impurity sources were used: (i) erbium-doped silicon plates were used as a source of fluxes of Er and Si atoms; and (ii) metallic erbium plates were used as an impurity-vapor source in combination with the silicon sublimation source. If gaseous oxygen was used for in situ codoping with erbium and oxygen, then concentrations ranging from 10¹⁸ to 10²⁰ cm^?3 were attained. When oxygen is in the growth chamber, the erbium-entrapment efficiency of a layer increases substantially, with the surface segregation of erbium also being suppressed by oxidation.     

Electroluminescence at 1.54 μm in Si:Er/Si structures grown by sublimation molecular-beam epitaxy

In Si:Er/Si diode structures grown by sublimation molecular-beam epitaxy in a vacuum with a pressure of ～10^?7 mbar at temperatures 520–580°C, the intensity of room-temperature electroluminescence at 1.54 μm is studied as a function of the concentration and distribution of erbium and donor impurities in the space-charge region (SCR) and the SCR width. Methods for obtaining electroluminescence in diodes with a wide (0.1–1 μm) SCR are developed. The mean free path of electrons with respect to their interaction with Er centers and the threshold energy a free electron needs in order to excite an Er-shell electron are determined. The values of electric-field strength corresponding to breakdown in silicon p-i-n diodes with and without Er doping are obtained experimentally. A model describing the interaction of hot electrons with Er centers is suggested.