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The results regarding formation of ITO/c-Si junctions interface through the oxidation of the silicon wafer are described. Thus the formation by this method of the thin layers SiO x with a thickness of about ~1nm is demonstrated, which allows obtaining photovoltaic conversion efficiency up to 15.3%. By depositing the luminescent layer on the front side of the ITO/c-Si junctions, which is active in the region of the solar cells sensitivity to the action of UV irradiation, their functionality in the range of 300 – 1100nm of the solar spectrum is demonstrated.

In this study, laser-treated polycrystalline Si (pc-Si) wafers, fabricated by wire sawing of hot-pressed ingots sintered from Si powder, have been investigated. As-cut wafers and those with high-quality thin Si layers deposited on top of them by e-beam have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser-treated Si powder-based substrates for fabrication of advanced Si structures has been analysed. It is established that (i) Si powder-based wafers with thicknesses ~180 μm can be fully (from the front to back side) or partly (subsurface region) remelted by a diode laser and grain sizes in laser-treated regions can be increased; (ii) a high-quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; and (iii) silicon nanowires can be formed by metal-assisted wet chemical etching (MAWCE) of polished Si powder-based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occur, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high-power laser treatments.

The fabrication of crystalline silicon thin films on foreign substrates is an attractive and alternative approach to the ingot casting aiming to the reduction of the total costs of photovoltaic cells and modules. The purpose of this work is to describe the CRYSTALSI process which aims at forming polycrystalline silicon films thanks to the thermal crystallization of amorphous silicon layer deposited on aluminium based substrates. The latest are used as a catalyzer for silicon crystallization but also as a back metal contact and reflector for photovoltaic solar cells. Two types of aluminium substrates were applied in these studies: a pure aluminium substrate (99.7% purity) and a silicon rich aluminium substrate containing about 12% of silicon. Silicon thicknesses between 1 and 10 μm were deposited and then annealed at temperatures of 490 °C, 520 °C and 550 °C and for duration times from 5 min to 12 h. The crystallized silicon films were then characterized by Raman spectroscopy, by scanning electron microscopy and by electron backscatter diffraction. The analyses show that the resulting annealed film is composed of two distinct layers: a thin polycrystalline silicon film located just above the substrate and a thicker layer made of a mixture of silicon and aluminium. Contrary to the case of the pure aluminium substrate, the silicon rich aluminium substrate allow to obtain thick and continuous polycrystalline silicon layers due to a controlled diffusion of the silicon within the substrate. As a result, the crystallization at 550 °C of 5 μm thick amorphous silicon on silicon rich aluminium substrate led to the formation of a thick polycrystalline silicon layer composed of grains of few micrometers in size. A low activation energy of about 2 eV is extracted suggesting that the silicon rich aluminium substrate is a catalyzer for the crystallization of amorphous silicon. As for the AIC process, it can be noticed that the limiting step of the CRYSTALSI process is the diffusion of the silicon in the aluminium. A chemical etching using a HNO 3 , HF, H 2 O (72.5 ml/1.5 ml/28 ml) solution is found to be appropriate to remove the residual top layer, in order to have access to the polycrystalline silicon layer. This work demonstrates that the CRYSTALSI process can lead to the formation of polysilicon films that can serve as a seed layer for the growth of a thicker absorbing silicon film for photovoltaic applications.

In this work, we studied the potential use of low-energy hydrogen implantation as a guide for the stress-induced cleavage. Low-energy, high fluence hydrogen implantation in silicon leads, in the right stiffening conditions, to the detachment of a thin layer, around a few hundreds nm thick, of monocrystalline silicon. We implanted monocrystalline silicon wafers with low-energy hydrogen, and then glued them on a cheap metal layer. Upon cooling down, the stress induced by the stressor layers (hardened glue and metal) leads to the detachment of a thin silicon layer, which thickness is determined by the implantation energy. We were then able to clearly demonstrate that, as expected, hydrogen oversaturation layer is very efficient to guide the stress. Using such process, thin silicon layers of around 710 nm-thick were successfully detached from low-energy implanted silicon wafers. Such layers can be used for the growth of very good quality monocrystalline silicon of around 50 µm-thick or less. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Homogenous aSi1−x Al x H y alloyed thin films, made by magnetron sputtering, has been found to exhibit tunable band gap and dielectric constant depending on their composition. The optical properties of alloys are largely defined by their electronic structure, which is is strongly influenced by interatomic charge transfer. In this work we have quantified interatomic charge transfer between Si, Al and H in aSi1−x Al x H y thin-films, with and . Charge transfer was found experimentally using x-ray photoelectron spectroscopy, by incorporating Auger parameter data into the Thomas and Weightman model. Both the perfect and imperfect screening models were tested, and the results were compared to models calculated using density functional theory based molecular dynamics. Using imperfect screening properties of Si and Al resulted in an excellent agreement between the experimental and computational results. Alloying aSi with Al is associated with donation of electrons from Al to Si for y = 0. For y > 0 electrons are transferred away from both Al and Si. The change in Si valence charge increases linearly with increasing band gap and decreasing dielectric constant. These relationships can be used as a quick guide for the evaluation of the Si valence charge and subsequently optoelectronic properties, at specific Al/Si ratios.

The realization of crystalline silicon thin films on foreign substrates is an attractive alternative to the ingot casting aiming at a reduction in total costs. The purpose of this work is to form polycrystalline silicon films using the crystallization of amorphous silicon deposited on aluminum (Al) substrates. The Al-substrate is used as a catalyzer for silicon crystallization but also as a conductive substrate and as a back reflector for the photovoltaic cell. The crystallization of 1-5 μm thick amorphous silicon films were carried out at a temperature of 550 °C and for duration times from 10 to 80 min. The crystallized silicon films were then characterized by Raman spectroscopy, scanning electron microscopy and by electron backscatter diffraction. The analysis show that the annealed layer is composed of two distinct layers: a thin polysilicon film located just above the Al substrate and on the top a thicker layer made of a mix of silicon and aluminum. The thickness of the polysilicon film is found to increase with the annealing time. The crystallization of 5 μm thick amorphous silicon during 80 min resulted in a 1 μm thick polysilicon layer composed of grains of few micrometers in size. The mechanisms of accelerated crystallization are discussed. Such polysilicon films can be used as a seed layer for the growth of a thicker absorbing silicon film for photovoltaic applications.

The purpose of this work is to verify the possibility to process highly doped Si supporting substrates using a 2-step process: (i) sintering of a low-cost Si powder based ingot using hot pressing and a ELKEM Silgrain material as a feedstock; and (ii) wafering of such ingots using multi-wire sawing technique similar to that, which is used for cast multi-Si or Cz-Si grown ingots. Moreover, the possibility to dope Si powder ingot at sintering temperatures below melting point of Si, using a mixture of Si and boron powders to fabricate highly conductive Si wafers is verified as well. The slurry technique has been chosen for multi-wire sawing of sintered Si powder based ingots. Surface properties of Si powder based substrates as well as their chemical composition have been studied by optical microscopy imaging and energy-dispersive X-ray spectroscopy (EDX). Although the overall concentrations of oxygen, carbon and possibly also metal impurities, which are initially present in a low-cost Si feedstock, are too high to achieve acceptable semiconducting properties, it is concluded, that sintered Si powder based wafers have high enough conductivity (resistivity ∼0.001 Ω cm) to serve as supporting substrates for low cost Si wafer equivalent structures.

The application of layers of doped colloidal silicon nanocrystals sandwiched between hydrogenated amorphous silicon layers as emitters in silicon heterojunction solar cells is explored. It is shown that such emitters provide excellent interface passivation and reasonable conductivity. Final solar cells with such nanoparticle emitters reach conversion efficiencies on the same level as solar cells with conventional hetero emitters. Quantum efficiency measurements indicate that the light absorbed in the nanocrystals contributes to the current extracted from the solar cell. The remaining challenges that need to be addressed before the application of such colloidal silicon nanocrystals for the processing of low-cost and potentially printable emitter layers becomes feasible are discussed.

One-step formation of silicon nanowires, sheets, and texture surface on a silicon substrate has been achieved using hydrogen-radical etching reactions. Metallic tungsten and for comparison purposes a tungsten hot wire, were used as catalysts for the hydrogen-molecular cracking. It was shown that a variety of surface structures on silicon such as inverted pyramid texture, V-groove texture, dense silicon nanowire growth over texture, and nanosheet structure can be obtained by controlling the process conditions. The obtained results suggested that the formation of nanotungsten silicide particle is an essential prerequisite to obtain these structures. The particles work as an etching mask against hydrogen-radical etching, as well as a catalyst for vapor–solid–solid (VSS) growth. SEM, TEM, micro-RAMAN, and XPS were used for the analysis of the hydrogen-radical-treated Si samples. The Si nanowires growth model, as well as the texturing mechanism initiated by hydrogen-radical treatment of Si surface in the presence of tungsten nanoparticle is discussed. It is concluded that the proposed acid-free method, which is based on a modification of Si surfaces only by hydrogen radicals, can be considered as a “green” technology approach, which can be used for the cost-effective fabrication of silicon nanostructures, which can be considered as a base for several types of advanced devices in the future.

A systematically prepared set of ITO layers for solar cell applications has been analyzed by spectroscopic variable angle ellipsometry in order to trace the dependence of free carriers' distribution along the film depth as a function of film thickness as well as its change upon annealing. Samples were deposited on silicon substrates with various thicknesses in steps of approximately 10-20 nm. This set was duplicated and these samples were annealed, so that for each thickness an as-deposited and an annealed sample is available. Conventionally measured electrical conductivity and morphological properties (AFM measurements) of the films have been compared with the optical constants' inhomogeneity, i.e. material properties along the film thickness modelled by variable-angle spectroscopic ellipsometry. The obtained results show that the optical as well as electrical properties of thin ITO films prepared by pulsed DC sputtering are depth dependent. For the deposition conditions used a well-determined reproducible non-uniform distribution of free carriers within the film thickness was determined. In particular it has been found that the majority of free carriers in as-deposited ultra-thin ITO films is concentrated at sample half-depth, while their distribution becomes asymmetric for the thicker films, with a maximum located at approximately 40 nm depth. The distribution of free carriers in annealed samples is qualitatively different from that of as-deposited layers. © 2012 Elsevier B.V. All rights reserved.

We investigated the formation of microcrystalline silicon (μc-Si:H) epitaxially grown on the polysilicon seed layer on the aluminium(Al) substrate using Electron cyclotron resonance plasma enhanced chemical vapor deposition method (ECR-PECVD). The μc-Si:H film serves as an active intrinsic absorber layer for a PIN configuration solar cell. A seed polysilicon (P+) layer was created by depositing amorphous silicon by ECR-PECVD method (using SiH 4 /Ar gases) directly on Al substrate followed by thermal annealing at 550°C resulting in a layer exchange. The μc-Si:H films was then deposited using a SiH 4 /H 2 gas mix employing the same reactor. The optimization of deposition parameters was carried out on mono crystalline-Si wafers. The parameters which allowed to reaching the highest crystalline fraction of ∼ 65% are obtained for SiH 4 =4 sccm, H 2 =40 sccm and a deposition temperature of 480°C. The Raman spectroscopy was carried out on the deposited films to determine the crystalline fraction while the spectroscopic ellipsometry measurements were applied to get an insight on the optical constants of the deposited layers as well as on their thickness. X-ray diffraction (XRD) measurements were taken to identify the crystalline phase of the deposited film and surface morphologies of films were observed by scanning electron microscopy (SEM).

In this work chemical liquid deposition from sol–gel solutions has been used to obtain thin (Al2O3)x(B2O3)1 − x dielectric films. Passivation of Si surfaces using these films has been studied. Morphological properties of thin films deposited on polished Si surfaces have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) technique. Their chemical composition, structural and optical features have been analysed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible (UV–VIS) spectroscopy. Results, obtained in this work, show that silicon surfaces can be effectively passivated by thin dielectric layers deposited from chemical solutions. The thin dielectric layers developed in his work, can be recommended as back side passivation coating for Si-based solar cells.

Hydrogen gettering and its out-diffusion from implantation-disturbed buried layers formed in oxygen-implanted silicon, annealed and subsequently treated in hydrogen plasma, have been investigated. Energy and doses of implanted oxygen ions were 200 keV and 1 × 1017 cm−2, respectively. After implantation Si:O samples were annealed at up to 1573 K, also under enhanced hydrostatic pressure, up to 12.3 kbar. Depending on processing conditions, disturbed buried layers, containing vacancy-like and other defects, SiO2−x clusters and/or precipitates, were formed. To produce hydrogen-enriched silicon structures, Si:O,H, with hydrogen accumulated within implantation-disturbed buried layers, Si:O samples were treated in hydrogen plasma. Out-diffusion of hydrogen from Si:O,H samples was investigated after annealing at 723 K and 973 K under atmospheric pressure. Depth profiles of oxygen and hydrogen were determined using secondary ion mass spectroscopy; X-ray reciprocal space mapping was applied for defect structure determination. Part of hydrogen remains to be present at surface and, especially, within implantation-disturbed areas even after annealing of Si:O,H at 973 K.

Properties of thin a-Si:H and indium-tin oxide (ITO) layers as well as properties of interfaces of Si based heterojunction (HJ) ITO/(p)a-Si:H/n-Si structures were analyzed by means of atomic force microscopy (AFM) and scanning spreading resistance microscopy. It is shown that the morphology of thin ITO layers grown on n-type polished crystalline Si or on (p)a-Si:H/n-Si substrates depends on the deposition temperature and has peculiarities on nano-scale. Formation of highly conductive nano-dots on the surface and in the bulk of ITO layers is found. The observed nano-spots and nano-dots are attributed to the influence of hydrogen initiated reduction process, which occurs upon deposition of ITO films on an a-Si:H layer during the fabrication process of a HJ solar cell. This fact is confirmed by investigation of morphological properties of ITO surfaces after treatment by hydrogen plasma. It is shown that formation of conductive nano-particles on the ITO surface initiated by hydrogen does not change essentially transparency of an ITO layer. It is concluded that conductive nano-dots at the ITO/a-Si:H interface can be considered as local conductive channels, which provide a current flow through the ITO/(p)a-Si:H interface without essential shadowing of the solar cell structure. This finding opens an interesting way for the optimization of properties of the ITO/Si-based HJ solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen gettering by implantation-disturbed buried layers in oxygen-implanted silicon (Si:O, prepared by O2+ implantation at energy 200 keV and doses 1014 cm-2 and 1017 cm-2) was investigated after annealing of Si:O at up to 1570 K, also under enhanced hydrostatic pressure, up to 1.2 GPa. Depending on processing conditions, buried layers containing SiO2-x clusters and/or precipitates were formed. To produce Si:O,H, Si:O samples were subsequently treated in RF hydrogen plasma. As determined by Secondary Ion Mass Spectrometry, hydrogen was accumulated at the sample surface and within implantation-disturbed areas. It was still present in Si:O,H (D=1017 cm–2) even after subsequent annealing at up to 873 K. Hydrogen accumulation within disturbed areas of Si:O as well as of SOI can be used for recognition of defects in such structures.

This paper describes the growth mechanism and structure of Si whiskers grown on a Si substrate in a tungsten hot filament chemical vapor deposition reactor with pure hydrogen as source gas using a two step process. In the first step, atomic hydrogen etched the silicon surface, forming silicon hydrides that react with tungsten from the filament. The resulting silicide particles deposited on the silicon surface forming a mesh-like pattern. The particles work as an etching mask against hydrogen radical etching of the silicon surface and inverted-pyramids or V-groove-shaped surface texture were obtained. In the second step the filament current was reduced and whiskers grew onto the substrate due to the interaction of the silicon hydrides with the particles and subsequent precipitation of saturated Si. The whiskers were found to have tungsten silicide particles on their tip, suggesting the whisker growth was through the Vapor–Solid–Solid (VSS) mechanism. A balance between the hydrogen radical etching effect and the supply of silicon hydride from the etching reaction on the silicon surface is crucial for the growth of dense silicon whiskers.

Hydrogen gettering by buried layers formed in oxygen-implanted silicon (Si:O prepared by O2 + implantation at the energy 200 keV and doses 10 14 and 10 17 cm -2 ) was investigated after annealing of Si:O at temperatures up to 1570 K, including also processing under enhanced hydrostatic pressure, up to 1.2 GPa. Depending on processing conditions, buried layers containing SiO2-x clusters and/or precipitates were formed. To produce hydrogen-rich Si:O,H structures, Si:O samples were subsequently treated in RF hydrogen plasma. As determined using secondary ion mass spectrometry, hydrogen was accumulated in sub-surface region as well as within implantation-disturbed areas. It has been found that hydrogen was still present in Si:O,H structures formed by oxygen implantation with the dose D = 10 7 cm -2 even after post-implantation annealing up to 873 K. It is concluded that hydrogen accumulation within the disturbed areas in Si:O as well as in SOI structures can be used for recognition of defects.

In this work, we report recent results of solar cells fabricated on silicon foils obtained by the Stress induced LIft-off Method (SLIM)-cut technique using an epoxy stress-inducing layer. Indeed, the use of silicon foils for the production of solar cells offers the ability to reduce material costs while allowing potentially a higher conversion efficiency. We show experimentally that silicon foil thicknesses between 40 and 140 μm can be tuned by changing the thickness of the epoxy. Standalone silicon foil based solar cells have been realized, and conversion efficiencies of 12.5% and 13.8% have been measured using 55 μm and 120 μm thick foils, respectively. In view of potential industrialization, mechanical support must be used during solar cells and module fabrication to avoid silicon foil breakage. Two different supporting substrates were therefore tested: an aluminum sheet and a sintered silicon substrate. Conversion efficiencies of 10.9% and 12.1% were obtained using 40 μm and 90 μm thick silicon foils on a polished Al substrate. Finally, a promising result of 13.1% was obtained after mini-module fabrication from 6 SLIM-cut solar cells (100 μm thick silicon foils) on the sintered silicon substrate using the i-cell concept.

Accumulation of hydrogen in Czochralski silicon implanted with N2+ (Si:N; N dose, DN=1–1.8x1018 cm-2; energy E=140 keV) or O2+ (Si:O; DO=1x1017 cm-2; E=200 keV), processed at up to 1400 K (HT) under enhanced Ar pressure, up to 1.2 GPa (HP), and followed by treatment in hydrogen (deuterium) plasma, was investigated by Secondary Ion Mass Spectroscopy. Implantation produces buried amorphous layer. As determined by transmission electron microscopy, subsequent HT-HP processing results in a formation of a specific sample microstructure. In plasma treated as-implanted Si:N, hydrogen accumulates at a depth of about 50 nm, up to concentration 2x1021 cm-3. This concentration is twice lower at a depth ≈ 80–250 nm. Deuterium content remains almost unchanged after plasma treatment of Si:N prepared by processing at 1270 K while it is strongly dependent on DN and on HP. In plasma treated Si:O, prepared by processing at 920-1230 K, hydrogen profile corresponds to that of implanted oxygen and decreases with HP. Comparative analysis of hydrogen accumulation and its subsequent release at 720-920 K in the Si:N and Si:O structures indicates that the capacity of buried layers in Si:O to getter and to preserve hydrogen is higher than that in Si:N.

In this work, an attempt to clarify the origin of a very pronounced effect of the minority carrier lifetime evolution in SiN x :H/a-Si:H/Si/a-Si:H/SiN x :H and a-Si:H/Si/a-Si:H solar cell structures prepared at temperatures around 200 °C upon heat treatments in the temperature interval of 445–550 °C is performed. For a comparison, heavily hydrogenated Si substrates were investigated as well. Analysis of all structures studied was performed by means of precise FTIR measurements and quasi-steady-state photoconductance (QssPC) techniques. Annealing-induced transformations of hydrogen-related states in Si-based structures upon heat treatments were monitored by a FTIR system with an enhanced sensitivity. Strong monotonic decrease of the intensity of various Si–H and N–H stretching bands was observed in all types of H-containing layers upon heat treatments applied. It is concluded that the transformations of H-related complexes in all structures studied are responsible for the observed changes in passivation efficiency of a-Si:H and SiN x :H/a-Si:H layers.

The goal of this work is to investigate the morphology, electrical and optical properties of undoped ZnO (i-ZnO) thin layers deposited on Si substrates with (100) and (111) orientations. Plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) was used for the deposition of i-ZnO layers at different temperatures. Atomic force microscopy (AFM), ellipsometry and four-probe method were used for the analysis. It is found that substrate orientation and growth temperature determine the morphological (grains size, surface roughness) as well as electrical properties of ZnO films. It is shown that the refractive index value depends on the surface morphology. It is concluded that properties of i-ZnO layers deposited on different Si substrates at different conditions exhibit some trends and peculiarities, which have to be taken into account for the processing of heterojunction solar cells by the PEMOCVD method.

Hydrogenated n and p doped Czochralski Si substrates have been studied by means of atomic force microscopy, scanning and transmission electron microscopy, Raman spectroscopy and microwave photoconductivity decay techniques. The measurements show that the surface is roughest in ndoped samples which are plasma treated at high frequency. The cone density was found to be highest on p-doped samples, which correlates well to the higher density of defects observed in pdoped samples. The surface cones were found to consist of nanograins, twins and stacking faults with random orientations, several hydrogen induced defects and bubbles. The size, density and formation depth of the subsurface defects were seen to depend on doping type, doping level, plasma frequency and hydrogenation time. Raman spectroscopy shows formation of nearly free hydrogen molecules, which are presumed to be located in nano-voids or platelets. These molecules dissolved at temperatures around 600°C. By means of the &-PCD measurements, it is demonstrated that hydrogen-initiated structural defects act as active recombination centres, which are responsible for the degradation of the minority carrier lifetime.

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to compare hydrogen defects formed in p doped [001] oriented Cz silicon samples which are H+ plasma treated , H+ implanted or Si+ implanted + H+ plasma treated. Samples were studied as processed and after annealing at 250°C, 450°C and 600°C. It is found that 1 hour H+ plasma treatment at 250°C produces a low density of large defects (~100 nm) in prefered {111} plans close to the surface. H+ implantation at a dose of 3x1016 cm-2 produces high density of small (~ 20 nm) mostly {100} platelets that after 1 hour annealing at 450°C result in microcrack formation. Lower H+ implantation doses form very few microcracks at this temperature. Silicon implantation with a dose of 1015 cm2 followed by 1 hour H+ plasma treatment at 250°C and 1 hour annealing at 450°C produces similar microstructure and microcracks as the 3x1016 cm2 H+ implantation dose.

Silicon hydrogenation is nowadays studied with the aim of developing and improving a technological method known as 'smart cut' used in the fabrication of 'silicon-on-insulator' devices. The goal of our study is to characterize the defects induced in silicon wafers after exposure to hydrogen RF plasma. Si001 wafers have been treated at 250 °C under hydrogen RF plasma at 110 MHz, for various durations. The main features observed by transmission electron microscopy (TEM) are surface roughening and the presence of three kinds of defects: {1 1 1} planar defects, {1 0 0} planar defects and H bubbles. In this work a study using conventional TEM and high resolution transmission electron microscopy (HRTEM) techniques is presented on H bubbles and {1 0 0} planar defects induced in Si wafers by H-plasma treatment. The strain field around the defects is qualitatively characterized by diffraction contrast analysis and quantitatively by the geometrical phase method, by processing the HRTEM images.

Transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used to study the temperature evolution of hydrogen plasma induced defects in silicon. Hydrogen plasma treated n- and p-doped Czochralski silicon samples were annealed at temperatures between 200 and 1000 °C for up to 10 h in air. Platelets are formed on {1 1 1} and {1 0 0} crystallographic planes. The structural defects are similar in n-type and p-type material. Small defects at the surface anneal out at temperatures above 400 °C and {1 1 1} platelets start to dissolve above 500 °C, except in highly p-doped samples where the platelets are stable up to 600 °C. The hydrogen penetrates deeper into a low doped than a high doped sample, resulting in platelet formation deeper into the sample. At annealing temperatures above 800 °C, an amorphous oxide layer forms at the surface of the sample. New platelets form after 1 h annealing at 1000 °C. The roughest surface is found in highly n-doped samples, hydrogenated at high plasma frequency for long exposure times. For high annealing temperatures the roughness decreases.

The mechanism of a low-temperature doping of silicon initiated by atomic hydrogen is studied. The formation of thermal donors (TDs) in direct-plasma hydrogenated n-type Czochralski silicon upon annealing at 450 °C is investigated by a combination of capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS). The expected hydrogen acceleration of TD formation is retrieved and the same goes for the introduction rate of the oxygen thermal donors (OTDs). It is shown that for short annealing times (30 min), the OTD concentration ( N OTD ) derived from DLTS is about one decade smaller than the increase in free carrier concentration (Δ n ), while for a 30 h anneal Δ n ≈ N OTD . From this, it is concluded that under the direct-plasma conditions used, other TD formation mechanisms occur simultaneously, involving H as an active participant, in combination with the radiation damage created during the plasma treatment.

Atomic force microscopy (AFM), scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) were used for the analysis of the morphology and electrical properties of heterojunction (HJ) solar cell structures made of Indium Tin Oxides (ITO) layers deposited on p-type polished Si substrates with a buffer layer of n-type hydrogenated amorphous Si (a-Si:H). By means of AFM measurements it is shown that the a-Si:H layer can be deposited on a Si substrate quite homogeneously with a roughness of only a few nanometers. In contrast, the morphology of the ITO layers depends on the deposition temperature and can be varied during the HJ solar cell processing. Cross section analysis of the HJ structures by SCM shows penetration of n-type carriers into the (p)Si bulk substrate and the formation of the resulting n-p electrical junction depends strongly on the ITO deposition temperature and the presence of the (n)a-Si:H layer. Complementary cross section SSRM measurements show only a highly n-type doped region confined to the ITO layer. Finally it is concluded that the properties of the HJ solar cell structures depend dramatically on the properties of the ITO layers and can be modified by variation of the ITO deposition temperature. (c) 2005 Elsevier B.V. All rights reserved.

Secondary ion mass spectrometry (SIMS) analysis of In, O, Si, and H concentrations versus depth distributions in ITO(In-Sn-O)/(n,p)a-Si:H/(p,n)-Si and ITO/(p)-Si heterojunction (HJ) solar cell structures was performed. SIMS measurements show some peculiarities of the element profiles in the interface of ITO/a-Si:H and a-Si:H/Si regions. These peculiarities can be attributed to the non-homogeneities (In-rich nanostructures, small dents or mounds) of the ITO layer. It is shown that the formation of In-rich nanostructures is more pronounced in case of ITO growth on a (p)a-Si:H/(n) Si substrate at 230 °C. SIMS profiles obtained from such non-homogeneous areas can show a penetration of In into the Si bulk, which is not a real distribution. A hydrogen redistribution from the a-Si:H layer into the neighboring ITO and Si layers in case of ITO/(n,p)a-Si:H/(p,n)-Si structures as well as hydrogen gettering to the ITO/(p)-Si interface was detected. It is concluded that the final heterojunction structure of ITO/(n,p)a-Si:H/(p,n)c-Si is rather complex and includes in addition to the individual ITO, a-Si:H and Si layers also intermediate ones with different composition.

Deep level transient spectroscopy (DLTS) has been performed on deuterated and non-deuterated p + -n - -n + Si-diode detectors made from oxygenated, low-doped, high-purity FZ-Si wafers. The deuterated samples were exposed todeuterium plasma at 150 °C for 2 and 4 h, respectively. All the samples were then irradiated with 6-MeV electrons to a dose of 2 x 10 1 2 cm - 2 . In the as-irradiated state the concentration of electrically active defects is the same in all groups of samples. The samples were subsequently annealed isochronally for 15 minutes at temperatures from 100 to 400 °C. No difference in the DLTS spectra is seen for the samples after annealing up to 200 °C. After annealing at 200 °C and above, however, pronounced differences in the annealing behaviour of the defects are observed. In the non-deuterated samples, the peaks of the two known divacancy levels (V 2 ) shift slightly during the annealing steps up to 300 °C. This shift is, from previous reports, ascribed to the interaction of V 2 with interstitial oxygen which results in the divacancy-oxygen centres (V 2 O). In the deuterated samples the two V 2 centres are fully annealed at 250 °C, without the transition to V 2 O. In the sample deuterated for 4 h the disappearance of the VO peak, starting during the annealing at 200 °C, coincides with the appearance of two peaks with positions at 0.17 and 0.58 eV below the conduction band, respectively.

In plasma-hydrogenated p-type Czochralski silicon, rapid thermal donor (TD) formation is achieved, resulting from the catalytic support of hydrogen. The n-type counter doping by TD leads to a p-n junction formation. A simple method for the indirect determination of the diffusivity of hydrogen via applying the spreading resistance probe measurements is presented. Hydrogen diffusion in silicon during both plasma hydrogenation and post-hydrogenation annealing is investigated. The impact of the hydrogenation duration, annealing temperature, and resistivity of the silicon wafers on the hydrogen diffusion is discussed. Diffusivities of hydrogen are determined in the temperature range 270–450°C. The activation energy for the hydrogen diffusion is deduced to be 1.23eV. The diffusion of hydrogen is interpreted within the framework of a trap-limited diffusion mechanism. Oxygen and hydrogen are found to be the main traps.

The effect of electron irradiation on n-type Cz- and oxygen-doped FZ-Si containing oxygen-related thermal donors (OTDs) due to a plasma hydrogenation and a subsequent thermal donor formation step at 450°C is investigated by capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. In order to explain the electron irradiation induced reduction of the carrier concentration, DLTS measurements were performed. They revealed the presence of thermal donors (TDs) and radiation-induced complexes. It is shown that the peak at E C -0.09 eV related to OTDs in CZ-Si diode is not changed by the electron irradiation.

Annealing at up to 1400 K of hydrogen plasma etched Czochralski silicon (Cz-Si:H) under enhanced hydrostatic pressure (HP) up to 1.1 GPa (HT–HP treatment) results in specific effects related both to the presence of hydrogen and to enhanced HP. The latter strongly affects the sample microstructure, precipitation of oxygen interstitials and creation of thermal donors (TDs). The HT–HP induced effects in Cz-Si:H are related to the HP stimulated creation of nucleation sites for the creation of TDs and oxygen precipitation as well as to decreased hydrogen out-diffusion under HP.

In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i ] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i ]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C – V ) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).

Depth resolved μ-Raman measurements were carried out on plasma hydrogenated and annealed silicon samples. The plasma exposure was done at 260 270 °C, and subsequent annealing at 450 °C or 550 °C. A thin structured plasma damage layer up to 100 150 nm depth and a subsurface layer up to a depth of ∼ 1 μm were observed by cross-sectional transmission electron and atomic force microscopy. In the subsurface region (111)and (100)-oriented platelets are located. Si-H Raman modes attributed to the plasma damage at the wafer surface exhibit a significant higher intensity than those attributed to platelets in the subsurface region. H2 molecules are located in the platelets, as was clearly seen by the fact that the H2 Raman signal exhibits a maximum in the intermediate subsurface region, where the platelets are located. After annealing hydrogen is released from the surface damage layer, while at the platelets it is still trapped.

Standard [001]-oriented p - (12–20 Ω cm) and n -type (1.8–2.6 Ω cm) Czochralski (Cz) silicon wafers were treated by a RF (13.56 MHz) hydrogen plasma at a substrate temperature of 250 °C. After the plasma hydrogenation subsequent annealing was applied up to 600 °C in air. The formation of H 2 molecules in voids/platelets was investigated by Raman spectroscopy. The Raman intensities of the H 2 vibration modes at ~4150 cm −1 exhibited significant intensity modulations in dependence on the annealing temperature. The intensities of the H 2 Raman lines indirectly monitor the evolution of the voids/platelets upon annealing. This assumption was verified by cross-sectional transmission electron microscopy (XTEM), which was applied for comparison. The intensity modulations of the H 2 Raman signal can be explained by the evolution of and platelets. At lower annealing temperatures ( 500 °C) platelets laying in planes are dominant, while at elevated temperatures ( ≥ 500 °C) [001]-oriented platelets become more and more important. platelets were also observed using XTEM measurements in p -type material. In case of p -type substrates the Raman intensities were significant higher than for n -type material. The higher H 2 Raman intensities in p -type Cz Si can be explained by the amphoteric character of hydrogen in silicon.

The modifications of the surface and subsurface properties of p-type multicrystalline silicon (mc-Si) after wet chemical etching and hydrogen plasma treatment were investigated. A simple heterojunction (HJ) solar cell structure consisting of front grids/ITO/(n)a-Si:H/(p)mc-Si/Al was used for investigating the conversion efficiency. It is found that the optimized wet chemical etching and cleaning processes as a last technological step before the deposition of the a-Si:H emitter are more favorable to HJ solar cells fabrication than the hydrogenation. Solar cells on p-type mc-Si were prepared without high-efficiency features (point contacts, back surface field). They exhibited efficiencies up to 13% for a cell area of 1 cm 2 and 12% for a cell area of 39 cm 2 .

The low-temperature photoluminescence (PL) measurements (down to 4.2 K) were employed for the investigations of the defects and impurities in multicrystalline silicon (mc-Si) samples grown by block-casting method. The optical properties of as-grown, irradiated by gamma-rays, heat and hydrogen plasma treated samples were studied. It was found that carbon and oxygen as the residual impurity atoms are responsible for the formation of the zero-phonon PL lines with 0.9355 eV (T line) and 0.9652 eV (I line) after heat treatments at about 350–550°C. The appearance of PL lines with the energies of 0.9697 eV (A line) and 0.7894 eV (C line) after a gamma-rays irradiation can be attributed to the formation of carbon- and oxygen-related centers, respectively. The comparison of the PL properties of the mc-Si samples with the mono-crystalline one is performed. It is shown that the main peculiarities of the low-temperature PL spectra of mc-Si can be explained both by the influence of residual impurities and the residual strains in this material.

Electrical activity of grain boundaries (GBs) and its transformation under the influence of low-energy hydrogen plasma treatment in p-type silicon bicrystalline samples cut from EFG silicon polycrystals were investigated. Comprehensive studies have enabled one to investigate the electrical activity of GBs relative to the minority (MIC) and majority (MAC) carriers and to demonstrate the possibility of controlling this activity by different processing methods. These studies allowed for establishing the correlation between the type, structure and individual electrical activity of GBs and also thermal pre-history of samples. Among the tested modes, hydrogenation was found to be the most radical method of electrical activity modification for all types of GBs. In the process, results on hydrogenation of GBs in EFG silicon crystals depend essentially on three factors: type of GBs, state of ribbons (as-grown or annealed) and concurrence of grain boundary dangling bonds and boron passivation effects.

Some crucial limiting process steps of ITO/(n)a-Si:H/(p)c-Si solar cell manufacturing were investigated. The influence of amorphous silicon deposition temperature on the efficiency of heterojunction (HJ) solar cells as well as ITO deposition on the properties of ITO/a-Si:H/c-Si interfaces were studied. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and SIMS measurements were employed for the investigations. It was observed that the decrease in a-Si:H deposition temperature from 230 down to 100°C leads to a reduction in solar cell efficiencies to only 1%. It was found that the ITO deposition process itself can significantly modify the ITO/a-Si:H/c-Si interfaces due to the interaction of oxygen, and In and Sn atoms with silicon at the initial stage. It was concluded that this modification has a more significant impact on the quality of the HJ solar cells than on that of the a-Si:H layer.

Hydrogensupportedthermaldonor(TD)formationwasobservedinoxygenenrichedhighresistivefloatzone(FZ)siliconbeingusedassubstratesfordetectorsintheLargeHadronCollider(CERN).TDformationwasprovidedbya‘‘2-step-process’’,consistingofaplasmahydrogenationat250 C(60min)andsubsequentannealingat450 Cinair(typicallyfor20–30min).Thesampleswereanalyzedbyspreadingresistanceprobe(SRP),CðVÞ andDLTSmea-surements.DopingbyTDsintheoxygenenrichedlayersofFZSisamplesmightbeapromisingmethodforthecreationofverydeep( 100lmÞ electricalfieldgradientsforanimprovedperformanceofSiradiationdetectors. 2002ElsevierScienceB.V.Allrightsreserved. Keywords: Float-zonesilicon;Oxygen;Hydrogen;Thermaldonors;Radiationdetectors 1. IntroductionSinceseveralyearsoxidizedhighlyresistivefloat-zone(FZ)siliconfacesstrongscientificre-searchinterest,sinceitwillbethebasicsubstratematerialfornuclearradiationdetectorsinfuturehighenergyphysicsexperimentsatthe‘LargeHadronCollider’atCERNinGeneva[1–3].Suchradiationhardsilicondetectorshavetosurvivehighenergyphysicsexperimentsrunningforperi-odsupto10years.Duringsuchlongoperationtimesthedetectorsareexposedtohighfluxesofparticles,andthereforetheysustainahighradia-tiondamage.Sinceapartoftheradiationinduceddefectsexhibitselectricalactivity,thedetectorscanbesignificantlyalteredduringlongtimeoperation.AcandidateforanelectricalactivedefectcenterinFZSidetectorsubstrates,whichmightbere-sponsibleforanegativespacechargeformationunder applied bias, is the di-vacancy-oxygen(V

The incorporation of hydrogen into the p-type Czhochralski (Cz) silicon by a plasma results in an enhanced thermal donor (TD) formation at temperatures around 400°C. Counter doping by the TDs and a rapid p–n junction formation occur in the p-type Cz Si. It is shown that the controlled TDs formation can be used for the low-temperature production of device structures: p–n junctions, p–n–p structures and structures with gradient doping. The characterization of the samples was done by the depth resolved spreading resistance probe (SRP) analysis. A kinetic model for the analysis of the hydrogen-enhanced TDs formation in the as-grown as well as in the Cz Si samples with denuded zone is developed. It can be concluded, that the controlled hydrogen enhanced TDs formation can be used as an alternative low-cost, low-temperature doping method, which might be favorable for active defect-engineering in the Cz Si.

The formation of H2 molecules in voids/platelets and their evolution upon annealing were studied. Standard p- and n-type Czochralski (Cz) silicon wafers have been treated by a hydrogen plasma at 2508C. After the plasma hydrogenation the samples were annealed at temperatures up to 6008C in air. Investigations were done byRaman spectroscopy. H2 did appear as nearlyfree molecules in the platelets/voids (Raman shift 4150 cm 1 ), but not on the tetrahedral interstitial position in the Si lattice. The normalized Raman intensities of the H2 vibration modes exhibited significant sensitivityto the annealing temperature for both p- and n-type Cz Si. These peculiarities can be explained by the evolution of the platelets during annealing. # 2001 Elsevier Science Ltd. All rights reserved.

Czochralski-grown silicon crystals with different carbon concentrations have been heat-treated in ?-wave hydrogen plasma in the temperature range 500-700??C. For comparison, control samples have been treated in a furnace in a nitrogen ambient. Infrared (IR) absorption measurements show that the loss of oxygen atoms from solution due to the formation of SiO2 precipitates is strongly enhanced by the H-plasma treatment in both carbon-lean and carbon-rich Si crystals. The loss of oxygen is accompanied by the loss of substitutional carbon atoms from solution in the C-rich samples. The frequencies and shapes of the IR absorption bands associated with the precipitates are different in C-rich and C-lean crystals, indicating the formation of different types of precipitate particle. The former bands (C rich) are similar following heat treatments in a H-plasma or in N2 gas. It is inferred that a fast diffusing species penetrates into Si crystals during the H-plasma treatment, leading to a catalytic enhancement of oxygen diffusion that in turn leads to enhanced precipitation. Possible mechanisms for the enhanced oxygen diffusion and precipitation are discussed briefly.

The effect of the gettering of hydrogen at buried defect layers at post-implantation hydrogen plasma treatments and the loss of hydrogen at these layers at high-temperature annealing of helium-implanted (at 300 keV, 1 × 10 16 cm -2 ; at 1 MeV, 1 × 10 15 , 1 × 10 16 and 1 × 10 17 cm -2 ) and, for comparison, of hydrogen-implanted (at 70 keV, 1 × 10 15 , 1 × 10 16 and 3 × 10 16 cm -2 ) Czochralski silicon was studied. The samples were annealed at 450 and 1000°C in flowing nitrogen or hydrogen ambient. As-implanted and annealed samples were treated by a d.c. hydrogen plasma at 150°C. Secondary ion mass spectroscopy (SIMS) was applied to measure the hydrogen concentration profiles of the samples. The buried defect layers, which were created by hydrogen or helium implantation, act as good getter centers for hydrogen at appropriate hydrogen plasma or heat treatments. It is shown that the loss of hydrogen from the buried layers depends on the temperature, the time of annealing and the annealing ambient. The loss of hydrogen at 450°C and the decrease of the hydrogen SIMS signal do not only result from a formation of H 2 molecules captured by cavities and platelets, but also from the penetration of atomic hydrogen into the wafer bulk. This penetration leads to a thermal donor formation, as can be proved by spreading resistance probe analysis.

The hydrogen-enhanced thermal donor (TD) formation in Czochralski (Cz) silicon is used for the characterization of the interstitial oxygen distribution by spreading resistance probe (SRP) analysis or by the carrier concentration from capacitance–voltage (C–V) measurements. For as-grown wafers or wafers with a denuded zone, the enhanced TD formation in Cz silicon has been studied by applying a hydrogenation from a plasma. A kinetic model for the hydrogen-enhanced TD formation is presented, and a method for the conversion of the carrier concentration due to TDs into a concentration of interstitial oxygen is proposed. For comparison, infrared spectrometry was applied for the characterization of the oxygen concentration in the samples. On the basis of the proposed model, the analysis by the SRP or C–V measurements of Cz Si samples containing TDs, which were generated with the support of hydrogen, can be used for the quantitative estimation of the distribution of interstitial oxygen in the as-grown wafers as well as, at least qualitatively, of the interstitial oxygen distribution in wafers with denuded zones.