Ivan Pelant - Academia.edu (original) (raw)

Papers by Ivan Pelant

Most of simple binary crystalline semiconductors have either zincblende (\(T_d\) face-centered cu... more Most of simple binary crystalline semiconductors have either zincblende (\(T_d\) face-centered cubic point-group symmetry) or hexagonal closed packed wurtzite structure (\(C_{6v}\) point-group symmetry) . They are derived from a cubic (fcc) or a hexagonal (hcp) structure.

Complex study of the fast blue luminescence of oxidized silicon nanocrystals: The role of the cor... more Complex study of the fast blue luminescence of oxidized silicon nanocrystals: The role of the core Lukáš Ondič, 2, a) Katěrina Kůsová, Marc Ziegler, Ladislav Fekete, Viera Gärtnerová, Vladiḿır Cháb, Václav Holý, Onďrej Cibulka, Katěrina Herynková, Mathieu Gallart, Pierre Gilliot, Bernd Hönerlage, and Ivan Pelant Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Cukrovarnická 10, 162 53, Prague 6, Czech Republic IPCMS, CNRS and Université de Strasbourg, 23, rue du Loess, F-67034 Strasbourg, France Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Na Slovance 1999/2, 182 21, Prague 8, Czech Republic Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic

We have seen in the foregoing chapters that the development of an effective Hamiltonian, which is... more We have seen in the foregoing chapters that the development of an effective Hamiltonian, which is adapted to the crystal symmetry, is an efficient tool to describe electronic excitations in semiconductors. The development procedure becomes, however, quite tedious and inefficient if a large basis of electron states is considered when describing a system. On the contrary, this technique is interesting if only a couple of almost degenerate states, which are well separated in energy from other states, has to be analyzed. This is the case for example in the exciton problem that has been discussed in the previous chapter. Here, the split-off exciton states (resulting from electrons and holes that transform as \( \Gamma _6\) and \(\Gamma _7\), respectively) are separated by the spin-orbit coupling from the exciton block obtained from electrons and holes that transform as \( \Gamma _6\) and \(\Gamma _8\), respectively. As we have already discussed, the two exciton blocks are coupled by the ...

Physica Status Solidi (a), 1998

Luminescence Spectroscopy of Semiconductors, 2012

Physica E: Low-dimensional Systems and Nanostructures, 2003

ABSTRACT In this contribution we present a new type of optoelectronic silicon nanocrystal (Si-nc)... more ABSTRACT In this contribution we present a new type of optoelectronic silicon nanocrystal (Si-nc) based material, namely, Si-nc embedded into solidified pure or doped spin-on-glasses. The resulting self-supporting samples contain thin layers with high Si-nc concentrations. The visible photoluminescence (PL) maximum at room temperature is blue-shifted when the concentration of phosphorus in the spin-on-glass is increased.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999

Many results have been obtained on the photoluminescence (PL) properties of Si nanocrystals embed... more Many results have been obtained on the photoluminescence (PL) properties of Si nanocrystals embedded in SiO 2 but very few about electroluminescence (EL) of Si/SiO 2 implanted layers. Thermally grown SiO 2 layers on Si have been implanted with high doses of Si and annealed at high temperature. Complementary techniques were used to characterize this structure. The implanted Si atomic distribution was determined by Rutherford Backscattering (RBS) measurements whereas the crystallinity of the layer was investigated by Raman scattering and XTEM. In particular, it was observed that Si nanocrystals, with typical dimensions larger than 10 nm, have been formed after the annealing step. A blue room-temperature EL (narrow peak at around 470 nm) was observed at high electrical ®elds. This study points out the importance of the capability of the electroluminescent structure to produce hot electrons.

Journal of Non-crystalline Solids, 1998

We report on study of the picosecond and femtosecond carrier dynamics in wide gap hydrogenated am... more We report on study of the picosecond and femtosecond carrier dynamics in wide gap hydrogenated amorphous silicon (a-Si:H). Samples of a-Si:H with band gap >2.1 eV were prepared from silane diluted with He by the microwave electron-cyclotron-resonance PE CVD and by the glow discharge decomposition. Pump and probe techniques were used to measure transient absorption on a picosecond time scale.

We report on two important features of light-emitting diodes based on a porous silicon p-n juncti... more We report on two important features of light-emitting diodes based on a porous silicon p-n junction: Strong decrease of the electroluminescence intensity is observed for pulses longer than-1 ms and the influence of ambient gases on the LED operation is discussed.

ABSTRACT We present time-resolved reflectivity, photoluminescence, dark conductivity and morpholo... more ABSTRACT We present time-resolved reflectivity, photoluminescence, dark conductivity and morphology studies of light-emitting Si prepared by pulsed XeCl laser irradiation of amorphous hydrogenated silicon (a-Si:H) deposited on a silica substrate by glow discharge deposition. Laser-induced melting and recrystallization of the a-Si:H layers lead to visible room temperature photoluminescence, accompanied by an increase in dark conductivity by more than three orders of magnitude. We investigate the influence of the number of applied laser pulses on the properties of the processed layers.

Silicon thin films were grown near the microcrystalline/amorphous boundary at substrate temperatu... more Silicon thin films were grown near the microcrystalline/amorphous boundary at substrate temperatures TS = 35--200°C and dilutions [H2]/[SiH4] = 25-167. The conductivity percolation threshold occurred at crystallinity ˜ 60%, above the random composite threshold 33.3%, due to amorphous tissue coating crystalline grains and limiting the electronic transport. Higher content of hydrogen at lower TS facilitates formation of ordered silicon phase

Solar Energy Materials and Solar Cells, 2003

Charge transport in microcrystalline silicon is strongly influenced by its heterogeneous microstr... more Charge transport in microcrystalline silicon is strongly influenced by its heterogeneous microstructure composed of crystalline grains and amorphous tissue. An even bigger effect on transport is their arrangement in grain aggregates or possibly columns, separated by grain boundaries, causing transport anisotropy and/or depth profile of transport properties. We review special experimental methods developed to study the resulting transport features: local electronic studies by combined atomic force microscopy, anisotropy of conductivity and diffusion length and also their thickness dependence. A simple model based on the concept of changes of transport path for description of the observed phenomena is reviewed and its consequences for charge collection in microcrystalline based solar cells are discussed.

Journal of non-crystalline solids, Aug 15, 2006

We search for the presence of stimulated emission in samples of porous silicon embedded in the so... more We search for the presence of stimulated emission in samples of porous silicon embedded in the sol–gel derived SiO2 matrix. By modifying the etching conditions of the porous silicon using hydrogen peroxide, we decrease substantially the nanocrystal size and produce a significant blue shift of the PL emission. Femtosecond variable-stripe length experiments combined with the shifting-excited spot technique demonstrates positive optical gain (modal gain∼ 25cm− 1) in the range 550–730nm. Ultrafast photoluminescence dynamics ...

Optical Materials, Feb 28, 2005

Stimulated emission from nanocrystalline silicon in the visible has become a hot topic during the... more Stimulated emission from nanocrystalline silicon in the visible has become a hot topic during the past years. Various forms of silicon nanostructures are being exploited, among them planar optical waveguides made of silicon nanocrystals, silicon superlattices and tiny silicon nanoparticles. We report on optical gain measurements using the variable-stripe-length and the shifting-excitation-spot methods in two different types of nanocrystalline samples: a planar nanocrystalline waveguide prepared by silicon-ion implantation (400keV, 4× ...

Journal of applied physics, Jun 1, 2006

Photoluminescence dynamics in silicon nanocrystals measured by a femtosecond up-conversion techni... more Photoluminescence dynamics in silicon nanocrystals measured by a femtosecond up-conversion technique are reported. The samples were prepared by embedding porous silicon grains in a sol-gel derived SiO 2 matrix. Efficient initial relaxation of the excess energy of photoexcited carriers with the effective rate≥ 3.8 eV/ps was observed. A fast decay component (400 fs) of the photoluminescence signal was found and interpreted in terms of quenching the interior exciton radiative recombination by carrier trapping on the ...

Applied physics letters, Apr 20, 2004

Porous silicon grains embedded in the phosphorus doped matrix exhibit improved photoluminesce pro... more Porous silicon grains embedded in the phosphorus doped matrix exhibit improved photoluminesce properties and better stability in comparison with native porous silicon samples. We have tested this material for the presence of room temperature optical amplification under femtosecond (100 fs, 395 nm) excitation. Combined variable stripe length and shifted excitation spot experiments reveal positive optical gain, the net modal gain coefficient reaching 25 at a pump intensity of 1.1 (mean power). The gain spectrum is ...

Beilstein journal of nanotechnology, 2018

We have fabricated two-dimensional photonic crystals (PhCs) on the surface of Si nanocrystal-rich... more We have fabricated two-dimensional photonic crystals (PhCs) on the surface of Si nanocrystal-rich SiO layers with the goal to maximize the photoluminescence extraction efficiency in the normal direction. The fabricated periodic structures consist of columns ordered into square and hexagonal pattern with lattice constants computed such that the red photoluminescence of Si nanocrystals (SiNCs) could couple to leaky modes of the PhCs and could be efficiently extracted to surrounding air. Samples having different lattice constants and heights of columns were investigated in order to find the configuration with the best performance. Spectral overlap of the leaky modes with the luminescence spectrum of SiNCs was verified experimentally by measuring photonic band diagrams of the leaky modes employing angle-resolved spectroscopy and also theoretically by computing the reflectance spectra. The extraction enhancement within different spatial angles was evaluated by means of micro-photolumines...

Physical Review B

We have studied the stimulated emission from an optically pumped graded index separate confinemen... more We have studied the stimulated emission from an optically pumped graded index separate confinement heterostructure, realized in the form of a metal-organic vapor-phase-epitaxy-grown single quantum well based on a wide-gap ͑ZnCd͒Se semiconductor. The structure is composed of a central Zn 0.78 Cd 0.22 Se quantum well sandwiched between two thicker, zinc-rich ͑ZnCd͒Se layers with a graded cadmium composition varying continuously and monotonously between 0% and 5%. The stimulated emission occurred at ϳ2.49 eV (T ϭ8.5 K), being spectrally redshifted with increasing temperature and disappearing for Tу200 K. The optical gain has been measured using the variable stripe-length method, and values of the gain up to 620 cm Ϫ1 have been achieved. High-resolution spectral studies of the stimulated emission have revealed a fine structure in the emission spectra originating from different localization sites for excitons. We identify the lasing mechanism as due to an inhomogeneously broadened system of localized excitons. ͓S0163-1829͑98͒04320-3͔

Proceedings of Spie the International Society For Optical Engineering, Apr 1, 2007

Description of optical waveguides is commonly restricted to propagation at distances much larger ... more Description of optical waveguides is commonly restricted to propagation at distances much larger than the width of the waveguide core and therefore only guided modes are taken into account in theory. Effects connected with leaking of the waves into the substrate may be, however, very important for possible applications in microelectronics. In this paper, we overview our model of photoluminescence