Papers by Author: N.A. Sobolev

Abstract: Defect structure, electrical properties and defect-related luminescence (DRL) of light emitting diodes (LED) with the active defect-rich region produced by oxygen implantation and a subsequent multistep annealing of silicon wafers were investigated. It was found that defect-rich regions possess an embedded positive charge in both n-and p-type of the samples whose origin was ascribed to oxygen precipitates (OP). The presence of that charge in the implanted region of p-based LED gave rise to the apparent conductivity type conversion and to a significant increase of free electron concentration in n-based LEDs. A significant difference in the shape and in the excitation dependence of luminescence spectra as well as in the properties of DLTS signals was found between p-and n-type samples. From an analysis of the obtained data the DRL band centered at 0.79 eV was ascribed to small OPs segregated at dislocations whose filling with the holes hinders optical transitions via dislocation-related states at 0.805 eV and the broad DRL band at energies higher than 0.81 eV was ascribed to large OPs.

Abstract: Structural defects induced by electron irradiation of n-Cz-Si wafers were identified. The influence of the annealing conditions in a chlorine-containing atmosphere on the structural and luminescent properties of the samples was examined and the optimal annealing conditions were found. Light-emitting diodes based on electron-irradiated and high-temperature-annealed wafers were fabricated by a vapour-phase epitaxy technique and their luminescence properties were studied. A high-intensity dislocation-related D1 line was observed at 1.6 μm in the room-temperature electroluminescence spectrum.

Abstract: Luminescent and structural properties of silicon layers with dislocation-related luminescence have been studied. Silicon ions (100 keV) were implanted into n-FZ-Si wafers at a dose exceeding the amorphization threshold by two orders of magnitude. The implantation was not followed by amorphization of the implanted layers. A post-implantation annealing resulted in the formation of luminescence centers and extended structural defects. Some fundamental aspects and specific features in the properties of dislocation-related luminescence lines and extended structural defects were revealed in relation to the annealing conditions.

Abstract: Structural and luminescence properties have been studied in silicon layers with dislocation-related luminescence. Multiple room temperature implantation of oxygen ions with doses low than the amorphization threshold was carried out. Silicon ions with a dose exceeding the amorphization threshold by two orders of magnitude were implanted at a higher temperature (≥ 80°C). Both the implantations were not followed by the amorphization of the implanted layers. Annealing in a chlorine-containing atmosphere resulted in formation of extended structural defects and luminescence centers. Some regularities and peculiarities in the properties of the extended defects and dislocation-related luminescence lines were revealed in dependence on the implantation and annealing conditions.

Abstract: Single crystal Si, Si0.948Ge0.052 and Si0.66Ge0.34 diodes as well as Ge transistor structures with high electroluminescence (EL) intensities in the region of interband transitions at room temperature were fabricated by different techniques and their luminescence properties were studied. By varying the Ge content in the solid solution, one can control the wavelength at the emission maximum in the range of 1.1 - 1.8 μm. The integrated EL intensity varies by a factor of less than two in the temperature ranges of 80 - 500 and 80 - 300 K for Si and SiGe LEDs, respectively. Si LEDs can effectively operate, at least, up to ~200°C. The data analysis shows that recombination involving excitons is the dominant mechanism of near-band-edge radiative recombination in all the light-emitting structures at room temperature. Some of the structures have record values of EL intensity and/or quantum efficiency, so they can be used as effective light emitters in Si optoelectronics. In particular, Si LEDs were designed with a small p-n junction area of 8x10-3 mm2 and a radiation power of 0.3 mW. The record total emission power of 46 mW was achieved in solar cell LEDs with an emitting surface area of 3 сm2. The internal quantum efficiencies of 0.5% and 0.3% were recorded in Si0.948Ge0.052 and Si0.66Ge0.34 LEDs at the wavelengths of 1.15 and 1.3 μm, respectively. Room temperature near-band-edge EL was first observed in Ge structures.

Abstract: Single crystal Si, Si0.948Ge0.052 and Si0.66Ge0.34 diode as well as Ge transistor structures with high electroluminescence (EL) intensities in the region of interband transitions at room temperature were fabricated by different techniques and their luminescence properties were studies. The analysis of the experimental data shows that recombination involving excitons is the dominant mechanism of near-band edge radiative recombination in all the light-emitting structures at room temperature. Some of the structures are characterized by record values of EL intensity and/or external quantum efficiency, so they can be used as effective light emitters for Si optoelectronics.

Abstract: Structural defects in Si:Er layers grown by molecular beam epitaxy have been studied by transmission electron microscopy. Two kinds of second phase precipitates are the main defects in the layers with Er concentration ≥ 2х1019 cm-3: ball-shaped precipitates (4-25 nm) of metallic Er localized at the layer-substrate interface and platelet precipitates of ErSi2 extending through the whole layer. We studied the effect of Er concentration (8х1018 - 4х1019 cm-3) and growth temperature (400 - 700°C) on the defect generation. The peculiarities of defect generation in MBE Si:Er layers implanted with B+ ions were also studied.

Abstract: Light-emitting diodes (LEDs) based on single crystal SiGe with the Ge content of 5.2% were fabricated using a planar technology. Their electroluminescence (EL) parameters were studied over a wide range of measured currents (up to 11 A) and temperatures (80 - 300) K. The integrated EL intensity at a fixed current increased approximately two times with temperature increasing from 80 to 200 K and changed insignificantly in the temperature range of 200 – 300 K. The analysis of the EL spectra shows that the recombination involving excitons is the dominant mechanism of radiative recombination at both no-phonon and phonon-assisted transitions in SiGe LEDs not only at low temperature but at room temperature, too. The linear dependence of the integrated EL intensity on the current and the exponential decay of the integrated EL intensity confirm this conclusion. The room temperature internal quantum efficiency of EL in the region of band-to-band transitions is estimated to be 0.5%. A sublinear current dependence of the integrated EL intensity and a fast decay of the integrated EL intensity after the diode turn-off were observed at room temperature and currents > 2.5 A. The effect is associated with the appearance of an additional (Auger) mechanism of non-radiative recombination parallel to Shockley-Read-Hall recombination.