E. Yu. Buchin

Different morphology aspects of n-type porous silicon

Abstract Four morphology types of pore structures, that were formed with optimal values of parameters of the system consisted of silicon wafer and electrolyte mixture while changing either temperature or wavelength of initializing irradiation were discovered. The results of optical and electrophysical measurements and physical-chemical analysis are discussed. The assumption concerning possible self-similarity of morphologies of both structures: macro- and micropores is put forward. The analysis of general regularities testifies to existence of the universal fractal mechanism of pores formation process.

Enhancement of the transversal magnetooptical Kerr effect in nanoperforated cobalt films

We present the technology of nanoperforated magnetic structures based on cobalt films deposited onto the surface of a porous aluminum substrate. The structures exhibit a significant (by an order of magnitude) enhancement of the transversal magnetooptical Kerr effect as compared to that in magnetic thin films formed on a usual nonporous substrate. The effect increases with the depth of pores.

Formation of porous nanostructured lead telluride films by an anodic electrochemical etching method

Comprehensive research of the structural, optical and electrical properties of a PbTe/CaF2/Si(1 1 1) epitaxial system after anodic electrochemical treatment in a Norr solution electrolyte with a low current density of 6 mA cm−2 was carried out. It is shown that the anodizing results in the increase of the band gap and resistivity and in the decrease of the refractive index of lead telluride. Using secondary ion mass spectrometry, a specific change of the C, K, H element distribution in depth of PbTe films after electrochemical treatment was detected. It is demonstrated that the set of presented experimental results can be explained from the standpoint of the formation of a mesoporous structure of lead telluride with a porosity value of about 50%. The effective radius of PbTe nanoparticles is equal to 13 nm. Triple-crystal x-ray diffractometry results analysis showed that the pores have spherical voids with an average dimension of 40 nm.

Forming through channels in silicon substrates

A new method of silicon processing, based on the selective electrochemical etching of p+-type regions formed in an n-type matrix by thermal migration of aluminum, is proposed. A special advantage offered by this technique is the possibility of obtaining through channels with a cross section of arbitrary shape and a characteristic transverse size ranging from 20 to 200 μm.

Fabrication of porous nanostructured lead chalcogenide semiconductors for modern thermoelectric and optoelectronic applications

Porous structures of lead chalcogenides with porosities of 20-68% and pore dimensions as small as 7-20 nm were fabricated using an anodic electrochemical etching technique applied to epitaxial PbTe and PbSe films on Si. Anodized lead selenide demonstrated two basic types of porous morphology: quasiporous noncontinuous layers and hierarchical porous layers. Lead telluride had a more typical mesoporous morphology, with pores propagating at an angle of 35° to surface, which corresponds to the <100< directions in the epitaxial films and is promising for the fabrication of photonic crystals with Yablonovite-like structure. The sizes of PbTe nanocrystallites in porous layers with high porosity were calculated to be 26 nm, which indicates that quantum confinement conditions are realized in this material. Such low-dimensional morphology of porous lead telluride is prospective for the fabrication of microscale thermoelectric devices with high ZT.

The structure of thermomigration channels in silicon

We have studied deep and through channels formed in n-Si wafers by means of thermal migration of thin discrete aluminum zones. The region of thermal migration channels was investigated using selective chemical etching of silicon in combination with secondary ion mass spectrometry for the analysis of impurity distributions. It is established that the channels are surrounded by two distinct peripheral shells.

Increasing adhesion of metallic films to silicon by ion bombardment during growth

Intense ion bombardment at the initial stage of film growth is used to increase the adhesion of nickel and vanadium films to silicon. The films are deposited by rf magnetron sputtering when a bias potential is applied to a substrate. The adhesion of metallic films to silicon is substantially increased due to active mixing of the contacting materials and the formation of a transition layer with a concentration gradient. A correlation between the adhesion of the films and their crystalline state is revealed.

Magnetomigration in granular cobalt-copper films deposited by the ion-plasma method

We have studied the effect of a constant magnetic field on the structure and composition of cobalt-copper (Co-Cu) granular alloy films deposited by the ion-plasma method. The phenomenon of magnetomigration of the main components and impurities has been observed. A necessary condition for this effect is a high mobility of adatoms, which has been achieved by ion-plasma deposition onto hot (200°C) substrates at high energies of incident metal ions. Under the action of an external magnetic field with strength above 300 Oe, both diamagnetic and paramagnetic adatoms migrate in opposite directions perpendicular to the field lines. Using this effect, it is possible to obtain thin magnetic films possessing high diamagnetic susceptibility and having a low content of undesired impurities (chlorine, hydrogen, carbon, argon, etc.).

Control of the morphology of n-type porous silicon

The morphology of layers obtained by anodic etching is related to the current-voltage characteristics of the electrolytic cell during the etching. By etching at various points of the current-voltage characteristic one can obtain porous silicon with various structures.

Different location of photo- and electroluminescence in n-type porous silicon

In the anodization process of n-type silicon a structure consisting of a nanoporous layer on top of a macroporous layer is formed. Many researchers believe that both photo(PL) and electroluminescence (EL) originate from the nanoporous layer [1 to 3]. We observed that the nanoporous layer was not homogenous and consisted of two sublayers (see Fig. 1a). It is stated that the top layer plays a key role in PL for n-type silicon while the bottom layer is responsible for EL.