Z. F. Krasilnik

Microscopic and optical investigation of Ge nanoislands on silicon substrates

We investigate self-assembled nanoislands in heteroepitaxial GeSi systems by means of atomic force microscopy and micro-Raman scattering techniques. We show that the surface diffusion of Si atoms from the substrate to the islands is strongly enhanced when the temperature increases, giving rise to a wider stability range of pyramid-shaped volumes.

Gigantic uphill diffusion during self-assembled growth of Ge quantum dots on strained SiGe sublayers

Raman spectroscopy and atomic-force microscopy were applied to study the morphology of nanoislands grown on strained Si1−xGex sublayers. It was shown that the growth of nanoislands on strained Si1−xGex sublayer not only induces the effect of their spatial ordering but also enhances the role of interdiffusion processes. Unusual high island volume increase during the epitaxy is explained by anomalous strong material diffusion from the sublayer into the islands, induced by nonuniform field of elastic strains.

SiGe nanostructures with self-assembled islands for Si-based optoelectronics

The effect of structure parameters on the electroluminescence and photoconductivity of multilayer structures with self-assembled Ge(Si)/Si(0 0 1) islands has been studied. The highest intensity of the room-temperature electroluminescence in the wavelength range of 1.3–1.55 µm has been observed for the islands grown at 600 °C. The same diode structures with Ge(Si)/Si(0 0 1) islands have demonstrated room-temperature photoconductivity signals in the wavelength range of 1.3–1.55 µm. The observed overlap of the electroluminescence and photoconductivity spectra obtained for the same structures with Ge(Si) islands makes these structures a promising material for the fabrication of a Si-based optocoupler. Less degradation after neutron irradiation has been observed for the electroluminescence and photoconductivity signals from multilayer structures with Ge(Si) self-assembled islands in comparison with bulk silicon structures. This result is associated with more effective confinement of charge carriers in the multilayer structures with Ge(Si) islands.

Photoluminescence of Ge(Si) self-assembled islands embedded in a tensile-strained Si layer

We report photoluminescence (PL) studies of Ge(Si) self-assembled islands embedded into a tensile-strained Si layer grown on smooth relaxed Si0.75Ge0.25∕Si(001) buffer layers subjected to chemical-mechanical polishing. The intense PL from Ge(Si) islands embedded into a strained Si layer compared to the PL from islands grown on unstrained Si(001) is associated with efficient confinement of electrons in a strained Si layer on the heterojunction with islands. The observed dependence of the island PL peak position on thickness of strained Si layer confirms the validity of the model for real-space indirect optical transition between electrons confined in the strained Si layer, and holes localized in islands.

Strain-driven alloying: effect on sizes, shape and photoluminescence of GeSi/Si(001) self-assembled islands

The effect of strain-driven alloying on sizes, shape and the photoluminescence (PL) properties of Ge(Si)/Si(001) self-assembled islands was investigated for temperatures of Ge deposition above 550 °C using atomic force microscopy (AFM), X-ray analysis, Raman spectroscopy. We found out that strain-driven Si diffusion into Ge/Si(001) self-assembled islands causes formation of an alloy in islands at these growth temperatures. An increase in the Ge content in the islands with a lower growth temperature results in a decrease of the pyramid-islands volume at which they transform to dome-islands. The energy of the optical transition in the free-standing islands was calculated using the observed values of the islands composition and elastic strain. The discrepancy between the calculated energy and the data observed from photoluminescence spectra is related to the changes of composition and height of the islands during Si overgrowth.

Effect of Space Charge Region Width on Er-Related Luminescence in Reverse Biased Si:Er-Based Light Emitting Diodes

In this paper, an effect of space charge region (SCR) width on Er-related electroluminescence (EL) in reverse biased Si:Er-based light-emitting diodes (LEDs) is under investigation. It is concluded that a trivial widening of the SCR in the examined LEDs with triangular and trapezoidal electric field profiles through SCR does not result in a desirable increase in the Er-related EL intensity. The tunnel transit-time diode structure with a complicated electric field profile through SCR is offered to increase the Er-related EL intensity. The difficulties hampering this process in erbium EL from reverse biased LEDs are under discussion

Effect of parameters of Ge(Si)/Si(001) self-assembled islands on their electroluminescence at room temperature

The electroluminescence (EL) of multilayered p-i-n structures with the self-assembled Ge(Si)/Si(001) islands are investigated. It is found that the structures with islands grown at 600°C have the highest intensity of the electroluminescence signal at room temperature in the wavelength range of 1.3–1.55 μm. The annealing of structures with the Ge(Si) islands leads to an increase in the EL-signal intensity at low temperatures and hampers the temperature stability of this signal, which is related to the additional Si diffusion into islands during annealing. The found considerable increase in the electroluminescence-signal intensity with the thickness of the separating Si layer is associated with a decrease in the elastic stresses in the structure with an increase in this layer’s thickness. The highest EL quantum efficiency in the wavelength range of 1.3–1.55 μm obtained in investigated structures amounted to 0.01% at room temperature.

Comparative analysis of photoluminescence and electroluminescence of multilayer structures with self-assembled Ge(Si)/Si(001) island

Comparative studies of the photoluminescence and electroluminescence of multilayer structures with self-assembled Ge(Si)/Si(001) islands are carried out. The luminescence signal from the islands is observable up to room temperature. Annealing of the structures induces a shift of the luminescence peak to shorter wavelengths. The shift is temperature dependent, making possible controllable variations in the spectral position of the luminescence peak of the Ge(Si) islands in the range from 1.3 to 1.55 μm. The enhancement of the temperature quenching of photoluminescence of the islands with increasing annealing temperature is attributed to the decrease in the Ge content in the islands during annealing and, as a result, to a decrease in the depth of the potential well for holes in the islands. The well-pronounced suppression of the temperature quenching of electroluminescence of the Ge(Si) islands in the unannealed structure with increasing pumping current is demonstrated.

Photoluminescence of dome and hut shaped Ge(Si) self-assembled islands embedded in a tensile-strained Si layer

The effect of the growth temperature (Tg) on photoluminescence of Ge(Si) self-assembled islands embedded between tensile-strained Si layers was studied. The observed redshift of the photoluminescence peak of the dome islands with a decrease of Tg from 700to630°C is associated with an increase of Ge content in the islands and with the suppression of smearing of the strained Si layers. The blueshift of the photoluminescence peak with a decrease of Tg from 630to600°C is associated with a change of the type of islands on surface, which is accompanied by a decrease in islands’ height.

Properties of optically active Si:Er and Si1-xGex layers grown by the sublimation MBE method

Abstract In this contribution we report on the application of the sublimation molecular beam epitaxy (MBE) method to grow efficient light emitting Si:Er structures as well the extension of this method to grow waveguiding Si 1− x Ge x layers. The formation processes of optically active Er centers in sublimation MBE grown materials and their properties are discussed. We distinguish the following optically effective Er centers in these materials: the oxygen-related Er-1 center, specific for sublimation MBE layers, a carbon-related center, SiO 2 -precipitate like centers and a variety of oxygen-related centers with low symmetry. The effect of the increase of photoluminescence efficiency in selectively doped structures, namely, in periodic multilayer Si–Si:Er/Si structures, has been discovered.