G. Yu. Rudko

Radiative recombination mechanism in GaNxP1-x alloys

Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.

Temperature dependence of the GaNxP1−x band gap and effect of band crossover

The absorption edge of GaNxP1−x alloys (0.01⩽x⩽0.03) is shown to exhibit a direct-band gap-like behavior. Thermal variation of the band gap energy Eg, however, is found to be the same or even smaller than that for the indirect band gap of GaP and depends on the N content. The effect is tentatively attributed to the following counteracting contributions to the band edge formation. An interaction with N-related localized states, especially significant in the vicinity of band crossover (e.g., x=0.013), causes a substantial slow down of the Eg shift with temperature. On the contrary, an increasing contribution of Γc states, which becomes predominant for the higher compositions, leads to the larger thermal variation in Eg.

Control of spin functionality in ZnMnSe-based structures: Spin switching versus spin alignment

The ability of attaining desired spin functionality by adjusting structural design is demonstrated in diluted magnetic semiconductor (DMS) quantum structures based on II–VI semiconductors. The following spin enabling functions are achieved by tuning the ratio between the rates of exciton spin relaxation within the DMS and exciton escape from it to an adjacent nonmagnetic spin detector. Spin switching is realized when using a thin layer of Zn0.95Mn0.05Se as a spin manipulator and is attributed to a fast exciton escape from the DMS preceding the spin relaxation. Spin alignment is accomplished in tunneling structures where the presence of an energy barrier inserted between a spin manipulator (a DMS-based superlattice) and a spin detector ensures a slow escape rate from the DMS layer.

Self-induced resonant optical rotation in crystals KCl:Li

Abstract The specific rotation of the resonant radiation polarization plane predicted earlier for cubic crystals with tunneling centers is observed in KCl containing FA(Li) centers. The rotation is supposed to be connected essentially with the well-known off-center position of Li+ ion. The simple theory based on this assumption agrees with the experimental data.

Simultaneous changes in the photoluminescence, infrared absorption and morphology of porous silicon during etching by HF

Changes in the photoluminescence (PL), microstructural morphology and the chemical nature of the surface of porous silicon (PS) when it is attacked with a 1:1 mixture of concentrated hydrofluoric acid and water have been studied. As the PS dissolves, the porous structure is essentially destroyed while the appearance and chemical composition of the surface change. At the same time, the intensity and peak wavelength of the PL change dramatically. The simultaneous investigation of PL, FTIR absorption and SEM observation of porous silicon layers (PSL) lend support to the view that chemical passivation, in particular by oxygen, is the major factor which controls the origin of PL. The PL intensity and the PL shift are ascribed to the changes in hydrogen and oxygen termination of pores.

Visible light emission from free-standing filament crystals of silicon

We present the results of a photoluminescence study in naturally grown filament-like silicon crystals. It is shown that with the decrease of filament diameter from few tens to 0.1 μm, the photoluminescence spectra transform from the ones of bulk silicon to completely new spectra. The spectra at 4.2 K consist of the narrow 1.139 eV band and several very wide visible (red, yellow, green, and blue) bands with the maximum position ranging from 1.7 to 2.9 eV. The bands of visible photoluminescence do not markedly change with the increase in temperature up to 300 K, while the 1.139 eV band disappears. The most striking result is the appearance of visible light emission from crystals with transverse size much larger than the Bohr radius. The results obtained are discussed together with our previous ones obtained for these crystals, and a possible model of the filament crystal structure as well as the origin of visible photolurninescence are suggested.

Enhanced activation of implanted phosphorus in silicon under rf plasma treatment

Abstract Photoluminescence of bound excitons is used to study the process of phosphorus activation in surface layers of implanted AlSiO2Si structures under rf nitrogen plasma treatment. It is shown that nonthermal process of phosphorus activation takes place at rf plasma treatment of silicon.

Temperature behavior of the GaNP band gap energy

Abstract We report experimental results from temperature dependence studies of the optical absorption edge of the GaNP alloys with N compositions up to 3.1%. The observed increase in the absorption coefficient with increasing N content, as well as the spectral shape of the absorption edge incline a band crossover to a direct band gap for the alloy, in agreement with previous studies. Temperature variation of the GaNP band gap, however, is found to be rather similar to that in the parental GaP, except for the N composition of ∼1% when a slow down in the thermally induced reduction of the band gap energy was observed due to a resonant interaction with the N-related defects. We thus suggest that both contributions from the interaction with the localized states and the increasing Γ character of the conduction band states are important for the alloy formation.

Photoluminescence of Anisotropically etched silicon

Visible room-temperature luminescence of Anisotropically Chemically Etched (ACE) silicon under “spontaneous” chemical surface modification in HNO3:HF solution is reported. The material is investigated by SEM, AES, IR transmission and Raman scattering methods.

Multiband light emission and nanoscale chemical analyses of carbonized fumed silica

Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible emission in annealed samples originated from inorganic pyrolytic carbon precipitates dispersed in the silica host matrix. Two types of emission bands were identified as a function of the annealing temperature: one is in the near UV and the other is in the visible range. Based on the emission/excitation analysis of these two bands, as well as on correlations with the synthesis conditions, a structural-energy concept of light-emitting centers has been proposed. According to this model, the light-emitting centers are associated with carbon clusters that can be bonded or adsorbed on the silica surface. This has been validated by a detailed (S)TEM-electron energy-loss spectroscopy study, confirming the inhomogeneous distribution of nanoscale carbon precipitates at the surface of the silica nanoparticles. These carbon precipitates are mostly amorphous although they possess some degree of graphitization and local order. Finally, the fraction of sp2 carbon in these nanoclusters has been estimated to be close to 80%.Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible emission in annealed samples originated from inorganic pyrolytic carbon precipitates dispersed in the silica host matrix. Two types of emission bands were identified as a function of the annealing temperature: one is in the near UV and the other is in the visible range. Based on the emission/excitation analysis of these t...