S. V. Svechnikov

Growth of III–V semiconductor layers on Si patterned substrates

Abstract Patterned unheated Si{100} substrates in the form of the regular tetragonal pyramids and a structure like hemispherical plates have been found to be effective for a pulse vacuum thermal deposition (pulse-VTD) of GaAs and GaP thin layers (50–500 nm). The effect of the pulse-VTD technological parameters (pulse duration, pulse period, pulse number, pulse current) and the features of the substrate patterns (terraces, steps, kinks, sponges) on the morphology, the composition and the crystallinity of GaAs and GaP layers have been characterized by scanning electron microscopy, electron X-ray analysis and electron diffraction.

Luminescent ZnS:Cu films prepared by chemical methods

For the first time, ZnS:Cu films with an intense photoluminescence were prepared by a chemical nonvacuum method. They were produced by means of the combined pyrolytic deposition of zinc and copper dithiocarbamates onto glass and ceramic substrates heated up to 260–300°C. A close packing of practically identical grains is characteristic of these films, with grain sizes depending on the substrate type. The photoluminescence and electroluminescence spectra include the blue, green, and yellow bands typical of copper. The band-intensity ratio depends on the film-preparation conditions, as well as on their excitation, which makes it possible to change the emission color of radiators in a wide range (from blue to white).

Optical properties of Si nanocomposite films prepared by laser ablation

Abstract Optical properties of thin films obtained by reactive pulse laser ablation of monocrystalline Si in He, O 2 or N 2 atmosphere have been studied. Both transmissivity and reflectivity of these films were measured in the range of 200–1200 nm and used for a calculation of their optical constants. The analysis of optical spectra has led to conclusion that the films prepared in this manner are composite structures containing at least two phases: the SiO x N y matrix and Si nanocrystallites embedded in it. We have shown good correlation between dependences of visible PL intensity and Si nanocrystallite sizes on preparation conditions.

Anisotropically etched Si surface and the electrical properties of Si/HgCdTe heterostructures

Abstract We used (001)-oriented silicon wafers, chemically etched under special conditions, as substrates for laser epitaxy of HgCdTe. Three types of Si surface with different microrelief were obtained: flat, pyramid-like and plate-like. Thin films of HgCdTe were deposited using a YAG:Nd 3+ laser. The electrical properties of the structures under investigation were analysed on the basis of current–voltage characteristics. These characteristics are interpreted in relation to the structural properties of the Si substrate surface. The carrier transport mechanisms for different HgCdTe/Si interfaces are presented.

Kinetics of exciton photoluminescence in low-dimensional silicon structures

Time-resolved photoluminescence (PL) spectra have been measured at 90–300 K in the visible spectral range for porous nanocrystalline silicon films fabricated by laser deposition. The energy and time ranges in which the spectra were taken were 1.4–3.2 eV and 50 ns–10 µs, respectively. The correlation between PL characteristics (intensity, emission spectrum, relaxation times and their temperature dependence), structure, and dielectric properties (size and shape of Si nanocrystals, oxide phase of their coatings, porosity of films) has been studied. A model of photoluminescence is adopted, in which the absorption and emission of photons occur in quantum-size nanocrystals, and in which kinetically coupled subsystems of electron-hole pairs and excitons are involved in the radiative recombination. Possible mechanisms of the exciton Auger recombination in low-dimensional silicon structures are proposed.

PLD of HgCdTe on two kinds of Si substrate

Abstract Films of HgCdTe have been obtained by pulse laser deposition method in dynamic vacuum (pressure∼10 −6 Torr) at 293–543 K. Two different kinds of Si surface were used as substrate: (a) flat standard polished {100} surface and (b) anisotropically chemically etched patterned surface. The results of a scanning electron microscopy investigation, electron probe microanalysis and I – V characteristic measurements showed a strong influence of the substrate kind on the morphology, composition, growth mode, growth defects and transport of HgCdTe/Si heterostructure.

Spectra of photoluminescence from silicon nanocrystals

The evolution of time-resolved photoluminescence (PL) spectra in Au-doped nanocrystalline silicon films produced by laser ablation has been studied. The PL spectra with a relaxation time of nanoseconds are broad; they lie in the energy range 1.4–3.2 eV with a peak at 2.4–2.8 eV. At the longest times of tens of microseconds, the spectra become narrower, with a peak at 1.6 eV. At intermediate times, two bands are observed: low-energy (1.6 eV) and high-energy, with the peak shifting from 2.7 to 2.1 eV with time increasing. The data are discussed in terms of quantum confinement, dielectric amplification, and manifestation of kinetically coupled electron-hole and exciton subsystems. Ions and atoms of gold passivate dangling bonds on the Si surface and serve as catalysts for the oxidation of nanocrystals. The similarity between recombination processes responsible for the visible PL in oxidized por-Si layers and in the studied Au-doped films is discussed.

Edge photoluminescence of single-crystal silicon at room temperature

The edge photoluminescence of single-crystal silicon (c-Si) with a peak at ∼1.09 eV at room temperature is observed for structures that consist of nanocrystalline silicon (nc-Si) and c-Si. The structures are obtained by pulsed-laser deposition of an nc-Si film onto a c-Si substrate. The photoluminescence signal increases as both the density of surface states at the nc-Si/c-Si boundary and the scattering of the edge emission from c-Si in the nc-Si film decreases.

SEM observation, photoconductivity investigation and I–V study of Si structures with patterned morphology for solar irradiance detection

Abstract Different types of silicon modified patterned substrates with and without p–n-junction were applied as a way for improving solar cells performance in order to prevent the light losses: (i) pyramid like (textured) surfaces (PrS); (ii) hemispherical plate like surface forms (PIS); (iii) dendritic structures (DS); (iv) porous morphology (LEPSi); (v) combinations of a textured surface with a porous one, etc. To realize them the anisotropical chemical and electrochemical etching in various etched mixtures and regimes, epitaxy and ion implantation were performed. Using scanning electron microscopy, spectral photoresponse measurements and current–voltage data, the morphological design, the variations in the photosensitivity, the wavelength peak position and the recombination parameters induced by the patterned processing and their influence for achieving the successful Si solar irradiance detection have been studied and analysed.

Photoluminescent and electronic properties of nanocrystalline silicon doped with gold

Doping nanocrystalline silicon (nc-Si) films grown by laser ablation with gold leads to a considerable suppression of the nonradiative recombination of the charge carriers and excitons, an increase in the intensity and stability of the visible photoluminescence, and enhancement of the low-energy (1.5–1.6 eV) photoluminescence band. In Au-doped samples, the magnitude of the photovoltage and the rate of electron capture by traps in the film are reduced, and the density of boundary electron states and the concentration of deep electron traps at the single-crystal silicon (c-Si) substrate are decreased as well. The observed effect of doping on the photoluminescent and electronic properties of nc-Si films and nc-Si/c-Si structures is caused by the passivation of dangling Si bonds with Au and by the further oxidation of silicon at the surface of nanocrystals, which results in the formation of high-barrier SiO2 layers.