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Four pairs of p-i-n structures based on polymorphous Si:H ( pm-Si:H) are fabricated by the method of plasma-enhanced chemical vapor deposition. The structures in each pair are grown on the same substrate so that one of them does not contain Ge in the i-type layer while the other structure contains Ge deposited by molecular-beam epitaxy as a layer with a thickness of 10 nm. The pair differ from one another in terms of the substrate temperature during Ge deposition; these temperatures are 300, 350, 400, and 450°C. The data of electron microscopy show that the structures formed at 300°C contain Ge nanocrystals ( nc-Ge) nucleated at nanocrystalline inclusions at the pm-Si:H surface. The nc-Ge concentration increases as the temperature is raised. The study of the current-voltage characteristics show that the presence of Ge in the i-type layer decreases the density of the short-circuit current in p-i-n structures when they are used as solar cells, whereas these layers give rise to an increase in current at a reverse bias under illumination. The obtained results are consistent with known data for structures with Ge clusters in Si; according to these data, Ge clusters increase the coefficient of light absorption but they also increase the rate of charge-carrier recombination. [ABSTRACT FROM AUTHOR]

The phase and elemental compositions of GeSi heterostructures deposited on non-refractory substrates are analyzed by using a non-destructive express technique, i.e., the Raman spectroscopy. It is shown that application of pulsed laser annealing allows one to vary the elemental composition and size of nanocrystals formed from solid alloys of germanium and silicon. [ABSTRACT FROM AUTHOR]

Mg2Si thin film was embedded in amorphous silicon matrix by solid phase epitaxy. The structure and optical properties were investigated by electron energy loss, X-ray photoelectron, Raman, and photo thermal deflection spectroscopy measurements. It was found that in the photon energy range of 0.8-1.7 eV, the light absorption of the structure with magnesium silicide (Mg2Si) film embedded in a-Si(i) matrix is 1.5 times higher than that for the same structure without Mg2Si. [ABSTRACT FROM AUTHOR]

Silicon nanocrystals are formed in the i layers of p-i-n structures based on a-Si:H using pulsed laser annealing. An excimer XeCl laser with a wavelength of 308 nm and a pulse duration of 15 ns is used. The laser fluence is varied from 100 (below the melting threshold) to 250 mJ/cm (above the threshold). The nanocrystal sizes are estimated by analyzing Raman spectra using the phonon confinement model. The average is from 2.5 to 3.5 nm, depending on the laser-annealing parameters. Current-voltage measurements show that the fabricated p-i-n structures possess diode characteristics. An electroluminescence signal in the infrared (IR) range is detected for the p-i-n structures with Si nanocrystals; the peak position (0.9-1 eV) varies with the laser-annealing parameters. Radiative transitions are presumably related to the nanocrystal-amorphous-matrix interface states. The proposed approach can be used to produce light-emitting diodes on non-refractory substrates. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon (a-Si:H) layers are prepared by plasma-enhanced chemical vapor deposition on metallized glass substrates. Ambient atomic force microscopy (AFM) is employed for both modification and characterization of a-Si:H films. Voltage pulses of up to 35 V are applied as a cantilever scans the amorphous silicon surface in contact mode AFM. Subsequent detection by Kelvin probe microscopy reveals a persistent negative charge stored in the a-Si:H layers. The stored charge is always negative independent of voltage polarity and results in an upward shift of the Fermi level by as much as 0.1 eV. Only at higher negative voltages (<-15 V) a positively charged oxide layer grows on the surface due to anodic oxidation. A model of the observed phenomena is proposed considering charge transport across a biased contact junction, metastable trapping in band-gap states of a-Si:H, as well as the influence of silicon oxide. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies two-dimensional maps of dark conductivity with submicron resolution obtained from in situ prepared hydrogenated microcrystalline silicon layers used for solar cells. Comparison of the morphology and current image; Identification of the silicon crystallites; Current decrease in grain boundaries.