Volume 17, Issue 5
October 1994, pages 1-561
pp 1- October 1994
pp 453-453 October 1994
pp 455-463 October 1994
A modified chemical deposition process is employed for the preparation of thin-film (CdS)x-(PbS)1 −x composites with 0·2 ≤x ≤ 0·8. Cadmium sulphate, lead acetate and thiourea are used as the basic source materials. The electrical conductivity is found to decrease with increasing composition parameterx up to 0·5 and increase for further increase inx. The composites are polycrystalline as is revealed from XRD and microscopic observations and show phases of both cubic and hexagonal CdS, cubic CdO and PbS, and tetragonal PbO and PbO2. Additional peaks of free elemental Cd and S have also been observed. For all the phases no significant variation in lattice parameters withx has been observed. The optical absorption studies show the presence of four well-defined absorption edges at approximately 0·45 eV, 1·05eV, 1·80 eV and 2·35 eV, at the same energies for allx values. The absorption coefficient is of the order of 104 cm−1 and mode of band-to-band transition is of the direct type.
pp 465-468 October 1994
n-CuInSe2 photoanode has been prepared by spray pyrolysis onto SnO2-deposited glass substrate. The effect of etching (HCl:HNO3=5 : 1 by volume) on photoanode properties has been studied. The best cell had the following parameters:Voc=0·446 V,Jsc=18·32 mA/cm2, ff=0·53 andη=6·22%.
pp 469-478 October 1994
Following physicochemical analysis, a kinetic model is described with a scheme of reactions in order to predict the growth rate and the compositional aspects of the ternary epitaxial layers GaxIn1 −xAs grown from Ga-In-As-Cl-H vapour phase. Theoretical expressions for the deposition rate have been derived in terms of experimental growth parameters and the relationship between growth kinetics and compositional aspects is investigated. Good agreement is obtained between the layer composition calculated based on the proposed model and the experimental values reported in the literature.
pp 479-486 October 1994
A process of fabricating n-type thermoelements by using abundantly available galena concentrate, including optimization of the sintering temperature and time, is reported in this paper. The results of variation of room temperature resistivity and thermoelectric power have been explained on the basis of inhomogeneities in the sample.
pp 487-492 October 1994
Two new ternary oxidic compositions of CuNiSnO4 have been prepared. The ternary composition Cu2+Ni2+SnO4 in orthorhombic symmetry with lattice dimensionsa0=5·773 ± 0·01 Å;b0=8·377 ± 0·01 Å;c0=10·094 ± 0·01 Å, while Cu+Ni3+SnO4 is also orthorhombic but with lattice dimensionsa0=5·737 ± 0·01 Å;b0=7·125 ± 0·01 Å andc0=10·071 ± 0·01 Å. The variation of electrical conductance with temperature indicates the semiconducting nature of these compositions. Hot-probe method indicatesp-type semiconduction in both the compositions
pp 493-498 October 1994
Dielectric properties of solution-gas interface-formed Fe(OH)3 thin-film capacitors (Al/Fe(OH)3/Al) of various thicknesses have been studied in the frequency range 10–106 Hz at various temperatures (300–443 K). Dielectric constant, ε, increases with increasing film thickness (d) and temperature (T) and decreases with increase of frequency (f). The loss factor (tan δ), showing pronounced minimum with frequency, increases with rise of temperature, and tan δmin shifts to a higher frequency. The large increase in dielectric constant towards low frequency region indicates the possibility of an interfacial polarization mechanism in this region.
pp 499-504 October 1994
A set of analytical expressions which can be used for estimating the effective speed of sound in porous materials is presented along with a brief description of the micromechanical origins of the analytical equations. These equations are validated and the accuracies are compared using published experimental data corresponding to four different ceramic materials.
pp 505-511 October 1994
We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ⩾ 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.
pp 513-522 October 1994
In this paper we discuss the different models proposed to explain the visible luminescence in porous silicon (PS). We review our recent photoluminescence and Raman studies on PS as a function of different preparation conditions and isochronal thermal annealing. Our results can be explained by a hybrid model which incorporates both nanostructures for quantum confinement and silicon complexes (such as SiHx and siloxene) and defects at Si/SiO2 interfaces as luminescent centres.
pp 523-531 October 1994
Porous silicon prepared with anodic currents of 5 to 30 mA/cm2 are characterized for structural and electronic properties of surface using photoluminescence, grazing angle X-ray diffraction, photoconductivity, thermally stimulated exo electron emission and work function measurements. The observed results indicate that with increasing porosity the crystallite size decreases and the amount of silicon hydride and oxide-type species increases, exhibiting a tendency similar to that of hydrogenated amorphous silicon and hydrogenated microcrystalline silicon. Free-standing powder of porous silicon, characterized by bright photoluminescence at 730 nm, showed crystallites of nanometre dimensions under the transmission electron microscope.
pp 533-550 October 1994
Room-temperature visible luminescence observed in porous silicon is one of the most significant discoveries of this decade as it opens up the possibility of silicon-based optoelectronics afresh. The exact mechanism of this different luminescence behaviour of porous silicon, compared to crystalline silicon, is not well established. In this paper results of a combination of infrared absorption, and photoluminescence emission and excitation spectroscopies will be described to show that the nanocrystallite nature of porous silicon and chemical environment at the surface are the important aspects of this novel luminescence behaviour.
pp 551-561 October 1994
Efforts have been made to see the effect of some standard microelectronic processing steps on porous silicon. Our diffusion experiments for making p-n junctions confirm that this material can withstand high temperatures of the order of 800°C to 1000°C. A new technique for photolithography has been suggested to obtain porous silicon in selected areas. Etch stop method to control the thickness of the porous layer and an organic protective layer for porous silicon have also been suggested. Models proposed by other workers to explain luminescence in porous silicon are not sufficient to explain many experimental observations. A hybrid model is suggested.
Volume 42 | Issue 6
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