V. A. Karavanskii

Ion implantation of porous gallium phosphide

The effect of irradiation by Ar ions and thermal annealing on the properties of porous gallium phosphide (por-GaP) obtained by electrolytic methods is investigated. It is shown on the basis of Raman scattering and photoluminescence data that, in contrast with porous silicon, por-GaP does not have high radiation hardness, and that thermal annealing of defects in layers amorphized by ion implantation is impeded by the absence of a good crystal base for solid-state epitaxial recrystallization processes. Data on radiation-induced defect formation and from probing of the material with a rare-earth “luminescence probe” are consistent with a mesoporous structure of the material.

Radiation hardness of porous silicon

The effect of irradiation by 300-keV Ar+ ions on the properties of electrochemically produced porous silicon is studied at doses of 5×1014–1×1016 cm−2. Raman scattering and photoluminescence data are used to show that the radiation hardness of porous silicon layers is substantially greater than that of single crystal silicon.

The structure of porous gallium phosphide

Free films of porous GaP have been obtained for the first time and their microstructure has been investigated by transmission electron microscopy (TEM) and Raman scattering (RS). The TEM results showed that the microstructure of the porous-GaP films has a complicated spatial structure, but the local crystallographic orientation is preserved and corresponds to the initial substrate. Narrowing of the half-width and a simultaneous low-frequency shift of the LO-phonon peak were observed in the RS spectrum. This behavior can be satisfactorily explained in terms of the change in the plasmon-phonon interaction as a result of a decrease in the carrier density. A shift in the frequency of surface phonons of porous GaP as a function of the local void formation conditions was also observed. It is shown that in principle porous layers can be obtained without the void surfaces being covered appreciably with oxides or other products of an electrochemical reaction.

Diamond-like and graphite-like carbon states in short-period superlattices

The Raman and luminescence spectra are studied in superlattices consisting of carbon layers separated by thin SiC barrier layers. It is shown experimentally that, upon the avalanche annealing of an initially amorphous superlattice, the carbon layers can crystallize into either a diamond-like or graphite-like structure, depending on the geometrical parameters of the superlattice. A method is proposed for obtaining carbon films with a specified crystal modification within a unified technology.

X-ray scattering by porous silicon modulated structures

A multilayered porous structure formed as a result of the anodization of a Si(111)(Sb) substrate in an HF:C2H5OH (1: 2) solution with a periodically alternating current has been investigated by high-resolution X-ray diffraction. It is established that, despite 50% porosity, a thickness of 30 μm, and significant strain (4 × 10−3), the porous silicon structure consists mainly of coherent crystallites. A model of coherent scattering from a multilayered periodic porous structure is proposed within the dynamic theory of diffraction. It is shown that the presence of gradient strains of 5 × 10−4 or higher leads to phase loss upon scattering from porous superlattices and the suppression of characteristic satellites in rocking curves.

Anomalous polarization of Raman scattering by transverse and longitudinal phonons in porous doped GaAs

The Raman spectra of a porous doped GaAs(100) crystal were studied. It is established that emission in the plasma-phonon spectra of both the starting and porous crystals is highly polarized and is independent of the incident-radiation polarization. It is inferred that the contribution of the Froelich mechanism to the intensity of the plasma-phonon spectrum is predominant and that the effects of defects and multiple scattering on the scattered-light polarization in porous GaAs may be ignored. The cause for the violation of the selection rules in the spectrum of porous crystal is discussed.

Influence of defects on the formation of thin porous GaP(001) films

The results are presented of the optical and X-ray studies of the structure of n-type subsurface GaP(001) layers implanted with 300 keV-He+-(D = 1016 at./cm2) and 600 keV-Xe2+-ions (D = 1012 at./cm2) and then subjected to electrochemical anodizing in aqueous 0.25 M H+ solution. It is shown that defects formed in the crystal lattice as a result of this treatment considerably influence the character of electrochemical etching and the structural parameters of the formed layers. It is shown that anodic etching proceeds over the defects, which allows one to obtain oriented systems of pores by choosing the appropriate conditions of preliminary implantation.

Light absorption and photoluminescence of porous silicon

The results of an experimental study of Raman scattering, photoluminescence, and light absorption and reflection in porous silicon layers obtained by electrochemical etching of single-crystal wafers are presented. It is concluded on the basis of an analysis of the experimental data that the centers responsible for radiative and nonradiative recombination in this material are of a multiple character. The experimental data show that the centers whose maximum of optical excitation lies in the blue-green region of the spectrum have a uniform distribution, in contrast with the centers whose region of efficient excitation lies in the red region of the spectrum. The radiative recombination efficiency of the latter increases in a thin, near-surface layer of a porous-silicon film.