M. V. Shaleev

Features of two-dimensional to three-dimensional growth mode transition of Ge in SiGe/Si(001) heterostructures with strained layers

The results of the study of the effect of strained SiGe layers on the critical thickness of two-dimensional growth of Ge layer in different SiGe/Si(001) structures are presented. A significant influence of buried strained SiGe layer on the growth of Ge has been found out, which remains considerable even for SiGe layers capped by unstrained Si layer of thickness up to 3.5 nm. The experimental results are well described by the proposed model, where obtained features are explained by means of introducing a phenomenological parameter called “effective decay length” of the strain energy accumulated in the structure.

Usage of antimony segregation for selective doping of Si in molecular beam epitaxy

An original approach to selective doping of Si by antimony (Sb) in molecular beam epitaxy (MBE) is proposed and verified experimentally. This approach is based on controllable utilization of the effect of Sb segregation. In particular, the sharp dependence of Sb segregation on growth temperature in the range of 300–550 °C is exploited. The growth temperature variations between the kinetically limited and maximum segregation regimes are suggested to be utilized in order to obtain selectively doped structures with abrupt doping profiles. It is demonstrated that the proposed technique allows formation of selectively doped Si:Sb layers, including delta (δ-)doped layers in which Sb concentrations can be varied from 5 × 1015 to 1020 cm−3. The obtained doped structures are shown to have a high crystalline quality and the short-term growth interruptions, which are needed to change the substrate temperature, do not lead to any significant accumulation of background impurities in grown samples. Realization of the p...

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.

Monolithically integrated InGaAs/GaAs/AlGaAs quantum well laser grown by MOCVD on exact Ge/Si(001) substrate

We report on realization of the InGaAs/GaAs/AlGaAs quantum well laser grown by metallorganic chemical vapor deposition on a virtual Ge-on-Si(001) substrate. The Ge buffer layer has been grown on a nominal Si(001) substrate by solid-source molecular beam epitaxy. Such Ge buffer possessed rather good crystalline quality and smooth surface and so provided the subsequent growth of the high-quality A3B5 laser structure. The laser operation has been demonstrated under electrical pumping at 77 K in the continuous wave mode and at room temperature in the pulsed mode. The emission wavelengths of 941 nm and 992 nm have been obtained at 77 K and 300 K, respectively. The corresponding threshold current densities were estimated as 463 A/cm2 at 77 K and 5.5 kA/cm2 at 300 K.

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.

Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 107 cm–2 and a root mean square roughness of less than 1 nm are obtained.

Photoluminescence line width of self-assembled Ge(Si) islands arranged between strained Si layers

The effect of variations in the strained Si layer thicknesses, measurement temperature, and optical excitation power on the width of the photoluminescence line produced by self-assembled Ge(Si) nanoislands, which are grown on relaxed SiGe/Si(001) buffer layers and arranged between strained Si layers, is studied. It is shown that the width of the photoluminescence line related to the Ge(Si) islands can be decreased or increased by varying the thickness of strained Si layers lying above and under the islands. A decrease in the width of the photoluminescence line of the Ge(Si) islands to widths comparable with the width of the photoluminescence line of quantum dot (QD) structures based on direct-gap InAs/GaAs semiconductors is attained with consideration of diffusive smearing of the strained Si layer lying above the islands.

Quantum Dot Emission Driven by Mie Resonances in Silicon Nanostructures

Resonant dielectric nanostructures represent a promising platform for light manipulation at the nanoscale. In this paper, we describe an active photonic system based on Ge(Si) quantum dots coupled to silicon nanodisks. We show that Mie resonances govern the enhancement of the photoluminescent signal from embedded quantum dots due to a good spatial overlap of the emitter position with the electric field of Mie modes. We identify the coupling mechanism, which allows for engineering the resonant Mie modes through the interaction of several nanodisks. In particular, the mode hybridization in a nanodisk trimer results in an up to 10-fold enhancement of the luminescent signal due to the excitation of resonant antisymmetric magnetic and electric dipole modes.

Transition from planar to island growth mode in SiGe structures fabricated on SiGe/Si(001) strain-relaxed buffers

The specifics of the two-to-three dimensional growth mode transition of pure Ge on SiGe/Si(001) strain-relaxed buffers (SRBs) were investigated. It was shown that the critical thickness for elastic relaxation is influenced not only by the lattice mismatch between the substrate and the film but also by Ge segregation and surface roughness dependent on parameters of strained layers. Critical thickness was found to be smaller for Ge grown on SiGe strain-relaxed buffers than on pure Si(001) substrates, in spite of the lesser lattice mismatch. Insertion of thin tensile-strained Si layers between Ge and SiGe strain-relaxed buffers increased the critical thickness.