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In this work, we study the optical response of structures involving porous silicon and porous alumina in a multi-layered hybrid structure. We performed a rational design of the optimal sequence necessary to produce a high transmission and selective filter, with potential applications in chemical and biosensors. The combination of these porous materials can be used to exploit its distinguishing features, i.e., high transparency of alumina and high refractive index of porous silicon. We assembled hybrid microcavities with a central porous alumina layer between two porous silicon Bragg reflectors. In this way, we constructed a Fabry-Perot resonator with high reflectivity and low absorption that improves the quality of the filter compared to a microcavity built only with porous silicon or porous alumina. We explored a simpler design in which one of the Bragg reflectors is replaced by the aluminium that remains bound to the alumina after its fabrication. We theoretically explored the potential of the proposal and its limitations when considering the roughness of the layers. We found that the quality of a microcavity made entirely with porous silicon shows a limit in the visible range due to light absorption. This limitation is overcome in the hybrid scheme, with the roughness of the layers determining the ultimate quality. Q-factors of 220 are experimentally obtained for microcavities supported on aluminium, while Q-factors around 600 are reached for microcavities with double Bragg reflectors, centred at 560 nm. This represents a four-fold increase with respect to the optimal porous silicon microcavity at this wavelength. [ABSTRACT FROM AUTHOR]

Modulated photoconductivity has proved to be an excellent tool to probe the density of states of semiconductors. However, though a great deal of attention has been devoted to the high frequency regime for its simplicity of application, the modulated photoconductivity in the low frequency (LF-MPC) regime has been the object of researches only recently. In the case of a dominant species of states present in the forbidden gap, it was shown that LF-MPC is a good complementary technique to the high frequency method to extract different transport parameters. In this paper, we present a complete theoretical analysis of the LF-MPC experiment for the case when different species of traps are present. We solve the complete system of equations that describe the experiment, and we apply simplifying assumptions to deduce a simple formula relating the photocurrent phase shift to the density of states (DOS) at the majority carriers’ quasi-Fermi level. By means of numerical calculations, we discuss the accuracy of our development, and of previous approximate formulas, to reconstruct a given DOS. Finally, we present experimental and theoretical evidence that, under sensitization conditions, the sign of the phase shift of the modulated photocurrent reverses and the steady-state photoconductivity depends superlinearly on the generation rate. [ABSTRACT FROM AUTHOR]

An experimental technique to study the energy profile of localized states in the gap of amorphous semiconductors is proposed. The method is based on the relationship between the recombination lifetime and the density of states (DOS) at the quasi-Fermi level for trapped carriers. We use the modulated photocurrent experiment in the recombination-limited regime as a convenient method to measure the recombination lifetime. Measurements performed as a function of temperature allow the DOS above the Fermi energy to be determined. The accuracy and limitations of the method are studied by means of computer simulations. The experimental technique is applied to obtain the density of defect states of a hydrogenated amorphous silicon sample. [ABSTRACT FROM AUTHOR]

Examines the kinetics of oxidation in high-pressure direct current-sputtered amorphous silicon (Si). Information on the two mechanisms of oxidation; Comparison between the density of α-Si and &alpha-Ge; Consequences of the existence of porous structure; Approximation of the total absorbance spectrum of the mixture.

Details a study which performed isothermal annealing on a hydrogenated amorphous silicon sample deposited at low temperature in a glow discharge reactor. Dependence of dark conductivity and photoconductivity on annealing time; Experimental procedures; Equation for computing the variation in photoconductivity.

Studies the amorphous silicon carbide samples by infrared and visible spectroscopy. Evolution of the 2000-2100 cm[sup-1] absorption band; Phases related to the Si-H bonds environments that exist; Factors that have the most important effect on the behavior of the band.

Presents a study which investigated the role of surface in sputtered amorphous silicon. Method of the study; Results and discussion; Conclusion.

Presents a study which reported the room-temperature cathodoluminescence (CL) of diamond like films produced by glow discharge. Details on the growth of films of crystalline diamond on substrates; Characteristics of CL spectra of diamonds; Details on the infrared spectra of the samples; Description of the normalized room-temperature CL of the samples.

Studies the oxidation of hydrogenated amorphous silicon carbide films prepared by glow-discharge decomposition of gaseous mixtures of silane and methane by using infrared absorption spectroscopy. Infrared differential absorbance spectrum of a carbon-rich sample obtained after six month room-temperature exposure to air; Overview of differential absorption spectra resulting from the oxidation of a sample; Presence of a large fraction of CH[sub3] precursor radical.