Yu. K. Undalov

Effect of electric field in the course of obtaining a-SiOx:H(Er, O) films by dc magnetron sputtering on their composition and photoluminescence intensity of erbium ions

The effect of electric field on the elemental composition and photoluminescence of films of amorphous hydrogenated silicon doped with erbium and oxygen (a-SiOx:H(Er, O)) in the course of obtaining these films by dc magnetron sputtering is studied. Two series of films were studied in relation to the electric-field strength in the magnetron, the area of the metallic erbium target, and oxygen content in the working chamber. The first series of films was obtained using an electrically insulated substrate holder, and the second series was obtained with a positive potential at the substrate holder with respect to the cathode. It is shown that, although the character of variation in the elemental composition and photoluminescence intensity for erbium Er3+ ions differ appreciably in the films of the two series, both of these factors are determined, as a result, by the processes of sputtering oxidation of the Si and Er targets that represent the cathode.

Silicon nanoclusters ncl-Si in a hydrogenated amorphous silicon suboxide matrix a-SiO x :H (0 < x < 2)

Published data concerning plasma methods of the fabrication and study of silicon nanoclusters ncl-Si in crystalline (c-SiO2) and amorphous (a-SiOx:H) matrices are reviewed. The effect of radio-fre- quency (RF) and direct-current (dc) discharge modulation on the growth kinetics of ncl-Si is considered. The results of infrared spectroscopy, mass spectrometry, and laser-beam scanning of the plasma composition are analyzed. The behavior of nanoparticles is described depending on their charge and size in plasma under the effect of electric, magnetic, and gravity forces and under the influence of the dynamics of gases contained within the plasma. Infrared spectroscopy data on the a-SiOx:H film matrix are analyzed. The photoluminescence properties of ncl-Si fabricated using different techniques are described.

Luminescence of amorphous silicon nanoclusters

Films of amorphous silicon suboxide α-SiOx containing amorphous silicon nanoclusters have been grown by direct current magnetron sputtering. It has been found that two radiation bands are observed in the photoluminescence spectra of relatively large amorphous nanoclusters (a size of ∼2 nm) unlike one photoluminescence band of silicon nanocrystals of the same size. The form of the spectra upon the change in the nanocluster sizes agrees with that predicted in theoretical works, in which the energy spectrum of amorphous nanoclusters has been calculated taking into account quantum confinement of delocalized, weakly localized, and strongly localized states.

Improvement of 1.54 μm luminescence in erbium-doped a-SiOx:H alloys

Abstract Erbium-doped amorphous silicon films have been deposited using magnetron-assisted silane decomposition (MASD) technique. The increase of partial concentration of O 2 in the gas phase above 6.5 mol% during the deposition enhances the intensity of the 1.54 μm Er photoluminescence (PL) at room temperature. The films exhibit an inhomogeneous structure containing oxygen and Er enriched nanoclusters, where the Er ions reside in optically active but electrically passive configuration.

On the formation of silicon nanoclusters ncl-Si in a hydrogenated amorphous silicon suboxide matrix a -SiO x :H (0 x < 2) with time-modulated dc magnetron plasma

Activation of the process of amorphous-silicon-nanocluster formation in a hydrogenated amorphous- silicon suboxide matrix with time-modulated dc discharge plasma is investigated. The plasma is modulated by repeatedly switching on and off a dc magnetron magnetic coil. It is demonstrated that the resulting self-induction effect leads eventually to an increase in the probability of collisions between discharge electrons and gaseous components. The infrared (IR) spectra of the films showed that plasma modulation enhances predominantly the content of bridging oxygen in the a-SiOx:H matrix by strengthening the oxygenionization process. It is assumed that this also increases the concentration of silicon nanoclusters ncl-Si with an oxidized outer surface in the plasma and, thus, enhances the ncl-Si flux toward the electrodes of the dc magnetron. The photoluminescence spectra include two broad overlapping bands characteristic of amorphous ncl-Si with maxima in the range of 600–1000 nm.

Peculiarities of the electronic structure and phase composition of amorphous (SiO2)x(a-Si: H)x–1 composite films according to X-ray spectroscopy data

Amorphous (SiO2)x(a-Si: H)x–1 composite films have been deposited from plasma of dc magnetron discharge switched on and off for variable periods of time. The electronic structure and phase composition of obtained films were studied by methods of ultrasoft X-ray emission spectroscopy (USXES) and X-ray absorption near edge structure (XANES) spectroscopy using synchrotron radiation. The results of a qualitative and semiquantitative analysis of the phase composition of films with the use of a special method of computer simulation showed that the content of amorphous a-Si: H clusters in SiO2 matrix can be varied within wide limits by changing the period of dc magnetron discharge switching. It is established that the formation of a large number of silicon nanoclusters in the (SiO2)x(a-Si: H)x–1 composite film leads to the appearance of anomalies in the XANES spectra, which are related to the scattering of synchrotron radiation on nanoclusters with dimensions comparable to the radiation wavelength near the X-ray absorption edge of silicon.

Comprehensive study of the conditions for obtaining hydrogenated amorphous erbium- and oxygen-doped silicon suboxide films, a-SiO x :H 〈Er,O〉, by dc-magnetron deposition

The results of a comprehensive study of the conditions for growing a-SiOx:H 〈Er,O〉 films are presented. The effect of the composition of various erbium-containing targets (a-SiOx:H , ErOx, Er2SiO5, Er2O3, and Er), substrate temperature, and annealing temperatures in argon, air, and under conditions of SiH4 + Ar + O2 plasma glow is studied. In order to obtain a-SiOx:H 〈Er,O〉 films with the highest photoluminescence intensity of erbium ions, it is recommended for the following technological conditions to be used: the substrate holder should be insulated from dc-magnetron electrodes and the working gas mixture should include silane, argon, and oxygen. Single-crystal silicon and metal erbium should be used as targets. The erbium target should be placed only in the Si-target erosion zone.

Excitation of erbium in the heterogeneous nanocrystalline matrix of amorphous silicon

The erbium photoluminescence decay kinetics at a wavelength of 1.54 μm in amorphous hydrogenated silicon films obtained at high oxygen concentrations in a magnetron gas discharge is investigated. Optically active erbium is found to exist both in the semiconducting matrix of amorphous silicon and in dielectric nanocrystals of erbium silicate, which are formed in this case. The concentration ratio of excited erbium in amorphous silicon and in the nanocrystals is determined, as well as the time of excitation transfer from erbium in amorphous silicon to erbium in the nanocrystals. The mechanism of erbium excitation in this heterogeneous system is considered. The external quantum yield of erbium photoluminescence measured at a wavelength of 1.54 μm and room temperature is found to be 0.3–0.4%.

A study of the effect of oxygen on the intensity of erbium photoluminescence in amorphous SiOx:(H, Er) films formed by DC magnetron sputtering

The effect of oxygen on the intensity of erbium photoluminescence at λ=1.54 µm in amorphous a-SiOx:H(Er) films formed by dc magnetron sputtering was studied. The oxygen content in the gaseous phase ranged from 0.1 to 12 mol %, with other parameters of deposition remaining constant. Analysis of an a-Si:(H, Er, O) system showed that the range of homogeneity of amorphous a-SiOx:H(Er) is retrograde (T=const). The range of homogeneity can be conventionally divided into two portions, each of which should contain either of two differently charged [Er-O]n− and [Er-O-Si-O]m− clusters (m>n). This inference is confirmed experimentally: in the range of oxygen concentrations amounting to 5.5–8 mol % in the plasma, unusual associative processes take place probably directly above the growing film surface; these processes are caused by the appearance of [Er-O-Si-O]m− clusters in the plasma and at the surface. It is these processes that account for the intensification of erbium photoluminescence as the oxygen content increases above 5.5 mol %.

Composition and Optical Properties of Amorphous a-SiO x :H Films with Silicon Nanoclusters

The phase composition and optical properties of hydrogenated amorphous films of silicon suboxide (a-SiOx:H) with silicon nanoclusters are studied. Ultrasoft X-ray emission spectroscopy show that silicon- suboxide films with various oxidation states and various amorphous silicon-cluster contents can be grown using dc discharge modulation. In films with an ncl-Si content of ∼50%, the optical-absorption edge is observed, whose extrapolation yields an optical band gap estimate of ∼3.2–3.3 eV. In the visible region, rather intense photoluminescence bands are observed, whose peak positions indicate the formation of silicon nanoclusters 2.5–4.7 nm in size in these films, depending on the film composition.