1,721,060 research outputs found
Photoreflectance line shape in quantum-confined semiconductor systems: the case of dilute nitrides
No full textPhotoreflectance technique has been extensively applied for studying the optical properties of quantum-confined semiconductor systems and for a long time the excitonic character of the intersubband transitions has been commonly accepted. The case of dilute nitrides deserves particular interest because of the unusual asymmetric aspect of their line shape, sometimes reported in the literature for quantum well related
transitions. The origin of the asymmetric line shape is clarified,
meanwhile showing how it can be used to acquire fine informations on the exciton binding energy and to investigate the N-induced variation of the electron eective mass in this class of semiconductor compounds
Infrared angular spectroscopy characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates
No full textIn this paper the technique of infrared angular spectroscopy applied to the characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates is illustrated. Some results are reported and discussed concerning films having a free-carrier concentration ranging from 1014 cm−3 to 1017 cm−3 and thickness of the order of 10 μm. A significant comparison with results obtained by other techniques (four-point probe, spreading resistance, C−V plots, etc.) is performed and a few simple conclusions are drawn
Effect of disorder on structures due to interband transitions in silicon
No full textThe optical response of silicon near the E1 structure, due to interband transitions, has been studied as a function of disorder by means of electroreflectance (ER). It is found that crystal grains smaller than the Rutherford backscattering (RBS) spatial resolution can still give rise to a measurable signal. The ER lineshape is briefly discussed and some important features are stressed
Oxygen impurities in epitaxial silicon grown on Czochralski substrates: recent advances by micro FTIR spectroscopy
No full textInvestigation of doping in Si crystals by means of electroreflectance
No full textIn this work the importance of electroreflectance is evidenced in two specific applications concerning studies of semiconductor surfaces: i) determination of junction depths and carrier profiles, ii) mapping of inhomogeneity curves of the carrier distribution on Si surfaces. New information in both cases is obtained and briefly discussed
Photoelectron–grain boundary scattering in al films of MOS structures
No full textInternal photoemission is studied in MOS structures by measuring the photocurrents obtained when the metal electrode – a thin Al film – is negatively polarized with respect to the Si slice and photons hv higher than the SiO2–Al interface barrier are impinging upon the structure from the metallic side. The data obtained by varying the thickness of the metal film are analyzed and a mean free path due to electron-grain boundary scattering of the order of the grain size is obtained
Step pseudomorphic asymmetric wells: an optical study in the framework of III-V strain induced sub-2D quantum systems
No full textAn optical study of the basic epitaxial structure for the fabrication of strain-induced sub-two-dimensional quantum systems was performed by comparing photoreflectance measurements with calculations of the energy positions and the relative intensities of the interband transitions originating in the different regions of
the sample. It is shown that by taking advantage of the explicit calculation of the overlap integrals associated with the asymmetric well transitions, the complicated optical response of the whole heterostructure can easily be interpreted. This, in
turn, enables the development of the optical investigation of the inner GaAs well (the active region of the device) by means of photoreflectance even at room temperature, as an alternative to the most commonly used low-temperature luminescence techniques
Optical study of the strain effect in pseudomorphic In1-xGaxAs-InP heterostructures
No full texthotoreflectance (PR) and optical absorption (OA) have been used to study the energy-gap dependence on temperature in In1-xGaxAs thin layers, metalorganic vapor-phase epitaxy grown on InP substrates under nearly lattice-matched conditions (‖Δa/a0‖≤10-3). Both PR and OA spectra show a split structure in the band-gap energy region. Moreover, the energy-gap values at all temperatures, obtained by Franz-Keldysh-oscillations analysis of PR line shapes, are blueshifted with respect to the values of the perfectly lattice-matched alloy (x=0.472). The results are related to the valence-band splitting at k=0 generated by the biaxial strain in In1-xGaxAs, due to the small lattice mismatch. We calculated the splitting and shift values using the orbital-strain Hamiltonian and accounting for compositional effects. The values are in agreement with the experimental results giving optical evidence of coherent growth of the alloy film
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