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In this study, we investigate the properties of n-doped amorphous silicon layer a-Si:H(n) combined with intrinsic thin silicon film deposited on high quality p-type CZ crystalline silicon, aiming at developing high performance heterojunction solar cells. The interface characteristics are analysed using Transmission Electron Microscopy TEM and capacitance measurements versus temperature and frequency. The insertion of a thin silicon film at the interface deposited under conditions of polymorphous material drives to a different structure of the interface. Our best front side heterojunction solar cells achieve 15% efficiency on 25 cm 2 , with an open-circuit voltage of 634 mV. A maximum open-circuit voltage of 676 mV has also been obtained on polymorphous/crystalline heterojunctions with a high quality rear local BSF, indicating the excellent interface passivation achieved with the intrinsic layer deposited in conditions of polymorphous silicon. This experimental study reveals the clear potential of p-type substrates for the development of amorphous/crystalline heterojunctions solar cells.

In this article we present an alternative approach for the fabrication of silicon nanocrystals (Si–nc) prepared ex situ of the silicon dioxide (SiO2) host matrix. The Si–nc are scratched from porous silicon layers and incorporated into a host spin-on-glass SiO2 based matrix. High-resolution transmission electron microscopy and Raman spectroscopy revealed Si–nc of 2–5 nm size. These nanocrystallites exhibit visible room temperature photoluminescence (PL) with a maximum at about 700 nm. The presence of the dopant in the host matrix is shown to induce a blueshift of the PL maxima due to modified surface states of the Si–nc. This approach allows the fabrication of self-supporting samples with very high Si–nc concentrations. A bright photoluminescence at room temperature is obtained on such materials. Finally, strong indication of optical gain at room temperature is shown for samples with high Si–nc concentrations in a phosphorus doped sol gel host matrix.

In this work, we investigate the potential use of silicon nanocrystals (Si-nc) into photovoltaics technology as one possible way to increase the silicon solar efficiency at low cost. The Si-nc were prepared ex situ (pulverizing of electrochemical etched porous silicon), embedded into spin-on-glass antireflecting SiO 2 based solution and then spun onto standard silicon solar cells. The Si-nc/SiO 2 layer serves as a luminescence down-converter. Indeed, the high energetic photons are absorbed within the converter ‘Si-nc’ and transformed via its photoluminescence (PL) to red ones (∼700 nm) which are then converted much more efficiently in silicon solar cell. We first quantify the size of the Si-nc. Then we present investigations of Si-nc based converter with different PL intensities and its influence on solar cell performances (internal quantum efficiency (IQE), current–voltage characteristic). We observe increase in IQE in the region where the PL of Si-nc appears. We also report the correlation between the converter PL intensity and IQE. To get insight into the potential of such converter, we introduced a simplified one-dimensional model. The results of the modelling are shown and compared with experimental data.

We present a new way to realise a selective emitter structure using a single screen-printed phosphorous paste deposition as dopant source to obtain a doping differential, with rapid thermal diffusion. The heavily doped part of the emitter is situated underneath the deposited phosphorous lines, and the lightly doped emitter in between is obtained via the gas phase, because phosphorous out-diffuses from the paste during the high-temperature step. SIMS profiles show a difference of a factor 4 in magnitude for the surface concentration between the regions underneath and beside the deposited paste. Photovoltaic results show an improvement in efficiency of 0.7% in comparison with the reference cell (homogeneous emitter), due to a 2mA/cm 2 short-circuit current increase.

The influence of a rapid thermal treatment on multicrystalline silicon produced by ElectroMagnetic Casting process (Emix® and Sitix®) and by directional solidification (Polix®), are investigated and compared in this paper. We have studied bifacial diffusion of phosphorus in this multicrystalline silicon and its gettering effect on the minority carrier lifetime measured by the photoconductivity decay technique. The diffusion is carried out by using a tungsten lamps furnace (rapid thermal processing (RTP)). This study shows an important lifetime improvement of multicrystalline silicon material produced by cold crucible casting compared to directional solidification.

In this paper, we study the effect of hydrogen-electron cyclotron resonance plasma (ECR plasma) on the phosphorous-doped emitter of a solar cell based on multicrystalline silicon (POLIX s ). The purpose of this experiment is to realise a selective emitter structure, using the front metal contacts as a mask. We show that hydrogen plasma etches the surface of the emitter away, and simultaneously diffuses into the silicon and increase the bulklifetime. Both minority carrier lifetime and etch rate depend on the grain orientation. Hydrogen diffusion is hindered by the high phosphorous concentration of the emitter, as shown on the SIMS profiles. Besides, SIMS profiles are revealing an anomalous behaviour of phosphorous, which diffuses into the silicon at temperatures as low as 3501C on (1 0 0) oriented grains. r 2002 Elsevier Science B.V. All rights reserved.

The formation of pn junctions and surface passivation by rapid thermal processing is being proved as a new and competitive method for silicon solar cell production. As the main process mechanisms are enhanced, the total process time at high temperature can be kept in the minute range, for the realization of emitter, back surface field (BSF) and surface passivation. In this work, we demonstrate for the first time that this knowledge, avoiding any in-situ annealing step acquired on the sc-Si, can also be applied on industrial mc-Si (Polix©) without bulk degradation, leading to a record conversion efficiency of 16·7%. Copyright © 2001 John Wiley & Sons, Ltd.

Rapid thermal processing is opening new possibilities for a low-cost and environmentally safe silicon solar cell production, keeping the process time at high temperature in the order of 1 min, due to enhanced diffusion and oxidation mechanisms. Controlling the surface concentration of the junction is one of the major parameters, in order to obtain suitable front surface recombination velocities. Simultaneous diffusion of phosphorus and aluminum is used to realize emitter and back surface field in a single high-temperature step, with optimized gettering effect. Controlling the mentioned parameters on industrial 1 Ω cm Cz material lead in 17.5% efficient solar cells on a surface of 25 cm2. All results are discussed in terms of process temperature, dopant source concentration and effective process time, below 1 min including high heating and cooling rates.

The electrical properties of boron-doped multicrystalline silicon for photovoltaic applications, elaborated by the cold crucible pulling process, are studied by the photoconductivity decay method and the electron beam-induced current measurement technique. The bulk lifetime mapping of the minority carriers in the as-grown silicon wafers is drawn up using both the techniques. Moreover, the consequence of phosphorus doping on the recombination properties of extended defects are studied using the EBIC measurements. Two different treatments are investigated in order to improve the electrical properties of the as-grown silicon wafers: (a) thermal phosphorus diffusion, for which the gettering efficiency is determined by the different treatment parameters; (b) remote plasma hydrogen passivation which leads to increase of the minority carrier lifetime.

Thin films of Si deposited by R.T.C.V.D. on (001) Si wafer were investigated on cross sectional sample using a JEOL 3010 high resolution microscope, in order to study the epitaxy and extended lattice defects formed during the deposition process in the film. H.R.T.E.M. images of extended defects were investigated by optical Fourier analysis in different areas of the picture; the results are interpreted in terms of twins and periodicity of twin lamellae. Further analysis from digital processing of the H.R.T.E.M. pictures was done by Gabor filtering and is interpreted in terms of strain field in the matrix.

The growth of epitaxial Si on (100)‐oriented Si wafers in a horizontal rapid thermal chemical vapor deposition (RTCVD) reactor has been investigated. Trichlorosilane was employed as a precursor diluted in carrier gas at 1 atm reactor pressure. The growth rates in dependence of the deposition uniformity, the input partial pressure of the precursor, and the fluid dynamics were analyzed by a three‐dimensional numerical simulation. Good agreement between predicted and measured growth rates were found. Moreover, the experimental growth rates under mass transport limitation were discussed in terms of gas‐phase supersaturation and its impact on the surface morphology. Finally, it is demonstrated that hydrodynamic effects in the RTCVD reactor influence strongly the Si growth in the delivery rate limited regime.

The various polycrystalline silicon materials (cast ingots, ribbons) which are commercially available for the solar cells manufacturing differ very much among themselves due to the different growth processes. The resulting microstructure and impurity content will influence differently the material characteristics during thermal treatments inherent to the device manufacturing. As the gettering efficiency depends on the kind of polycrystalline material, the variations observed in the optimal gettering conditions or passivation will be discussed. In this paper, we compare the performances of various types of polycrystalline silicon upon classical and rapid thermal-process-induced co-diffusion of phosphorus and aluminium. We show that a large bulk minority carrier diffusion length enhancement occurs in the case of co-diffusion when compared to the separate diffusion of phosphorus and aluminium.

The crystal structure of Nd2Fe14B has been analysed at 20 and 290 K by using the four-circle X-ray diffraction technique. The room temperature tetragonal structure (space groupP42tmum) has been accurately determined. At low temperature, the monoclinic distortion (space groupCm) proposed from a recent neutron diffraction experiment has been fully confirmed.

In this work, we present results on simultaneous formation of emitter/back-surface field or emitter/surface passivation in a single rapid thermal cycle. We have investigated the diffusion kinetics of dopant elements like phosphorus, boron (from a doped spin-on glass (SOD) film), aluminium (from evaporated films) or aluminium-boron (from an A1-B SOD film). In particular, we have shown that rapid thermal co-diffusion of P and A1 (or A1-B) leads to low sheet resistances, optical emitter profiles and a hig h gettering effect. Furthermore, the possibility of using the remaining SOD films as a surface passivation layer was investigated. Dark saturation current measurements as deduced from the photoconductivity decay technique demonstrate the passivation effec t of the remaining SOD film. The highest efficiency of 12.8% obtained was achieved on SOD oxide-coated solar cells.

Epitaxial growth of silicon films over the temperature range from 900 to 1300 °C was investigated in a rapid thermal chemical vapour deposition reactor working at atmospheric pressure. The growth of boron doped Si was performed from trichlorosilane and trichloroborine diluted in hydrogen. The epilayers were analysed by Rutherford backscattering spectroscopy, specular reflectance, scanning electron microscopy and Nomarski microscopy. Mechanisms for the observed growth rate are examined, and are tied closely to the degree of surface coverage by Cl. The electrical properties of the deposited films were also checked using the spreading resistance and the four point probe techniques.

The impact of carbon and oxygen on the performance of high efficiency photovoltaic devices is still poorly understood. As oxygen is one of the dominant impurities present in silicon, various applications require different levels of oxygen to improve the device performance. In this work, we have studied the effects of the oxygen concentration in silicon on the co-diffusion of phosphorus and aluminium by rapid and conventional processes. We will compare the effectiveness of the co-diffusion of P-Al in a variety of silicon materials, as a function of temperature and duration of the thermal process in a classical and a rapid thermal furnace and examine the influence of carbon and oxygen on the gettering efficiency. In particular, we will show that the large enhancement of the minority carrier diffusion length (LD) due to this process can be related to the presence of oxygen and carbon, the influence of which during the thermal cycle is of importance.

The external gettering effect by phosphorus diffusion is used to improve the minority carrier diffusion length of polycrystalline silicon. Large grain silicon wafers are exposed to a POCl3 source at different temperatures and durations and are afterwards post-annealed in a conventional diffusion furnace in a pure argon atmosphere. The influence of the starting and quenching temperatures of the post-annealing step on the gettering efficiency is investigated. The optimisation of the thermal annealing cycle parameters, i.e. the determination of the best combination of starting temperature of post-annealing, heating and cooling rates, post-annealing temperature and duration, pull-out temperature of the wafers, and POCl3 diffusion conditions, results in a large improvement of the minority carrier diffusion length in camparison to the starting material. A further advantage of this post-annealing is the improvement of the homogeneity of the active phosphorus distribution and of the electrical properties. Um die Minoritatsladungstragerdiffusionslange von polykristallinem Silizium zu verbessern, wird der externe Gettereffekt benutzt. Groskorniges Siliziummaterial wird mit Hilfe einer POCl3-Quelle verschieden lange und bei verschiedenen Temperaturen dotiert. Die Proben erhalten anschliesend unter reiner Argonatmosphare in einem konventionellen Diffusionsofen einen sogenannten „post-anneal”. Dabei wird der Einflus der Anfangs- und Endtemperaturen (Temperatur beim Herausziehen der Proben) des „post-annealing” -Schritts auf die Getterwirkung untersucht. Die Optimierung der einelnen Parameter des thermischen „annealing” -Ablaufs, d. h. die Bestimmung der besten Kombination der Anfangstemperatur des „post-annealing”, Aufheiz- und Abkuhlraten, „post-annealing” -Temperatur und Zeitdauer, Endtemperatur der Silizium-Scheiben sowie POCl3-Diffusionsbedingungen, ergibt eine gravierende Verbesserung der Minoritatsladungstragerdiffusionslange im Vergleich zum Ausgangsmaterial. Ein zusatzlicher, positiver Effekt dieses „post-annealing” ist die uber die Probenflache verteilte Homogenitatssteigerung der aktiven Phosphor-Verteilung und der elektrischen Eigenschaften.

Nous avons etudie les effets du recuit thermique rapide sur la precipitation de l'oxygene dans differents materiaux de silicium. L'augmentation de la concentration en oxygene interstitiel apres un recuit thermique rapide est due a la dissociation et a la dissolution de certains microprecipites existant dans le materiau, qui dependent essentiellement de la quantite initiale d'oxygene, de l'histoire thermique du materiau, des defauts et impuretes residuelles.

Rapid thermal annealing (RTA) was investigated for curing doped and undoped spin-on glass films deposited onto silicon substrates. The annealed undoped spin-on glass (SOG) films present an important densification of the layers as a function of temperature and a reduction in the interfacial state density. The possibility of using rapid thermally annealed spin-on doped glass (SOD) films as a doping source as well as a surface passivation layer was investigated. The results show that the combination of spin-on film (after dilution of the solution with methanol) deposition and RTA can produce shallow lightly doped emitters. Sheet resistances lower than 150 Ω/□ are easily reached. Moreover, the minority-carrier diffusion length is improved owing to the gettering effect induced by phosphorus diffusion. The use as a passivation layer of the SOG or the remaining SOD oxide film makes this technique favourable for applications such as the fabrication of solar cells.

Rapid thermal processing can offer many advantages, such as small overall thermal budget and low power and time consumption, in a strategy focused on cost-effective techniques for the preparation of solar cells in a continuous way. We show here that this very short duration (a few tens of seconds) of isothermal heating performed in a lamp furnace can be used for many thermal steps of silicon solar cell processing. Rapid thermal processing was applied to form the p-n junction from a phosphorus-doped spin-on silica film deposted on (100) silicon substrates at typical processing temperatures between 800 and 1100°C. the solar cells showed conversion efficiencies as good as those processed in a conventional way.

Large CeRu2Si2 and Ce1−xLaxRu2Si2 single crystals have been grown using a “tri-arc” Czochralski technique. The structures of the ternary silicides are characterized by the exchange of transition metal and silicon positions. The existence of a small amount of random “mixed crystallographic sites” between ruthenium and silicon has been carefully studied. Single crystals of CeRu2Si2 were grown from different starting compositions. Microprobe analysis and low temperature X-ray single crystal structural investigations were used. Neither a shift from the ideal composition, nor disorder between ruthenium and silicon were found. The pure sample and its solid solution with LaRu2Si2 are compared.

A combination of procedural algorithms and predicate logic formalisms is proposed to generalize complex coastlines. The advantage of this combined strategy is to cover both the geometric and conceptual aspects of the generalization process. The geometric part is dedicated to simplification and displacement operations for graphical presentation. The conceptual part handles the problem of river selection based on geometrical and semantic criteria. The derivation of a hierarchical model reflecting the hierarchical structure of the bay/river network of the coastline is a requirement for river selection. A case study was carried out, and results show an improvement over more conventional procedural approaches. The idea of building a hierarchical model to prepare the ground for feature selection can be applied to other hierarchically structured objects such as road networks or nested buildings in urban areas.

Diffusion of phosphorus into silicon from a doped spin‐on glass source using rapid thermal processing is described. The structural and electrical characteristics of the resulting shallow junctions including atomic and carrier concentration profiles, sheet resistance, as well as the effects on bulk carrier transport properties were studied and compared to those resulting from the use of conventional furnace heating. The results show that sheet resistance as low as 15 Ω/⧠ and surface carrier concentration higher than 1 × 1020 cm−3 are obtained in the annealed samples. Furthermore, a gettering effect is observed as the minority‐carrier diffusion length measured by the surface photovoltage technique is improved after processing.

Nous montrons dans ce travail que l’hydrogene, qui est un element leger diffusant rapidement dans le silicium, passive non seulement les liaisons pendantes et les defauts cristallographiques inter-ou intra-grains dans les materiaux polycristallins, mais egalement les impuretes chimiques qui sont responsables en tant que centres de recombinaison de la degradation des proprietes de transport du materiau.

Automated line reduction of digitally encoded geographic lines may produce a topologically distorted view of the line morphology. Such distortions appear in the form of self-crossings, closing peninsulas, and spikes. Geometric procedures for the removal of point-to-point and point-to-line collisions are described. The procedures intervene after reduction, hence they are independent from the methods being used. The robustness of the solutions is tested both in the removal of collisions between spatially conflicting elements and in the broader context of neighborhoods, where displacements are propagated throughout the region surrounding the colliding elements. This is an important step between simple line reduction and automated generalization.

This paper presents a synergy of ant colony optimization (ACO) and particle swarm optimization (PSO) into a novel hybrid coordination algorithm for distributed multi-agent systems. The intended multi-agent systems are composed of relatively simple, expendable agents with highly decentralized, self-organized behaviors; which as a whole achieve global optimization over a set task. Basically, two coordination processes among the agents will be established. One is a stigmergy-based algorithm using the distributed virtual pheromones to guide the agents' movement, the other one is interaction-based algorithm, where a global maximum of the attribute values can be obtained through the interaction between the agents. The simulation results demonstrate that the proposed hybrid swarm intelligence based architecture is feasible, efficient, and robust to coordinate a simulated distributed multi-agent system

In this paper, we present a hybrid ant colony optimization/particle swarm optimization (ACO/PSO) control algorithm for distributed swarm robots, where each robot can only communicate with its neighbors within its communication range. A virtual pheromone mechanism is proposed as the message passing coordination scheme among the robots. This hybrid ACO/PSO architecture adopts the feedback mechanism from environment of ACO and the adaptive interplay among agents of PSO to create a dynamic optimization system, and it is well-suited for a large scale distributed multi-agent system under dynamic environments. Furthermore, a pheromone-edge pair propagation funneling method is developed to reduce the communication overhead among robots. The simulation results concretely demonstrate the robustness, scalability, and individual simplicity of the proposed control architecture in a swarm robot system with real-world constraints

Rapid thermal processing for junction formation is emerging as a low cost technique for solar cell as well as for other semiconductor device production. Compared to conventional furnace processing, process differences are not only in very high heating and cooling rates, but also in the incoherent emitted radiation spectrum, which can act on dopant diffusion. The photons emitted from tungsten halogen lamps go from far ultraviolet, over visible to infrared light. In this work additional mercury ultraviolet lamps are used during rapid thermal annealing to analyze the influence of high energetic photons on diffusion mechanisms. The diffusion results are discussed in terms of radiation spectrum, involving analysis of diffusion profiles and sheet resistances.

In this work we present a procedure to extract very fine silicon nanocrystals (Si-nc) from porous silicon powder and to correlate their structural properties to their optical characteristics. The silicon nanocrystals (Si-nc) were fabricated ex situ by electrochemical etching of silicon (porous silicon) and then embedded into a silicon dioxide host matrix made of spin-on glass (SOG). This approach allows the study of Si-nc behaviour directly in the colloidal solutions (ethanol, spin-on glass silicon dioxide) by light scattering. Light scattering experiments revealed aggregation of Si-nc in such solutions. We show that these clusters can be disaggregated by adding ammonia and/or phosphorous oxide to the solution. Total disaggregation is recorded and the Si-nc size obtained corresponds to the values measured by various techniques such as HR-TEM, micro-Raman and small angle x-ray scattering. Furthermore, we show that the presence of phosphorus in the spin-on glass host matrices leads to a blue shift of the photoluminescence maxima as well as declustering the Si-nc in the spin-on glass within minutes.

We have investigated the formation of silicon nanocrystals (Si-nc) ex situ of the silicon dioxide host matrix as well as their structural and optical properties. Two different methods were used: Si-nc prepared by electrochemical etching as reference and Si-nc fabricated by ball milling. We show that both methods are able to prepare Si-nc with quantum confinement size (

The authors have designed a new back surface field (BSF) solar cell with a substructure of the multi-interface L-H type. Some normally separate phenomena are taken into account simultaneously to model a complex interface inserted in the cell emitter. The theoretical modelization and one-dimensional numerical simulation (using the PC-1D software package) show its yield to be 35-40%. In practice, this would necessitate uniting recent technological advances in the same thin sub-structure to ensure: (i) the absorption of low energy photons; (ii) the optical confinement of the infrared light; and (iii) the formation of an inserted highly doped thin film (/spl delta/-doping properties). >

In this paper, the authors investigate the simultaneous processing of the emitter junction and the emitter surface passivation by rapid thermal annealing (RTA) from a doped spin-on glass (SOG). Test structures and solar cells of different emitter profiles and surface concentrations were made by diluting two different doped spin-on glass liquids with methanol. By this procedure, oxide thickness and doping can be controlled. RTA was performed in an argon atmosphere in the temperature range of 850/spl deg/C-1000/spl deg/C for 5-60 sec. The results show that emitter surface doping concentration between 1*10/sup 19/ cm/sup -3/ and 3*10/sup 20/ cm/sup -3/ and junction depth from 0.1 /spl mu/m could be obtained. Sheet resistances lower than 150 /spl Omega///spl square/ could be easily reached. External quantum efficiency measurements from solar cells, made from CZ and FZ p-type silicon wafers, demonstrate the passivation effect of the remaining SOG-film. The highest efficiency obtained with this ohmic back contacted cells, which had an oxide thickness of about 70 nm, are 12.8%.

Rapid thermal processing (RTP) using radiation from tungsten halogen lamps as a heat source is a very promising candidate to replace conventional furnace annealing as it offers many advantages such as a reduced overall thermal budget and a lower gas consumption. In this paper, the authors show that with moderate temperature, RTP can be used to obtain screen printed contacts with low contacts resistivity and without degrading the transport properties of the solar cell base region. They investigate on Polix multicrystalline solar cells the possibility to replace the conventional sintering by a RTP annealing of the Ag front grid and of the back Al/Ag contact in a single step performed after the antireflection coating deposition.

Rapid thermal processing (RTP) is now emerging as a promising simplified process for manufacturing of terrestrial solar cells in a continuous way. In earlier works, we have shown that RTP can advantageously replace the classical furnace for performing emitter, BSF and surface passivation in addition to an efficient gettering of metallic impurities during these steps. In this work, we present results about co-diffusion of two dopant elements in a single rapid thermal cycle at low temperature in order to form emitter and BSF simultaneously. We have, in particular, found that the diffusion kinetics of dopant elements are enhanced during rapid thermal co-diffusion of P, Al or B and lead to the optimal dopant activity and profile for high efficiency silicon solar cells at low temperature. Additionally, the gettering effect induced by the co-diffusion of P and Al is more efficient than can be achieved by a single diffusion of these two elements. Finally, test solar cells were performed on these structures and gave, for a low processing temperature (800/spl deg/C/60 s), an efficiency of 11% on polished FZ monocrystalline substrates without antireflecting coating.

Experiments carried out by RF glow discharge on phosphorus-diffused N/sup +/P junctions have shown that hydrogen neutralization only takes place in the 300-400 degrees C temperature range. The observed increase of the bulk diffusion length L/sub D/ is completely lost if post annealing is performed at temperatures higher than the stability of hydrogen bonds with defects or impurities (i.e., 450-500 degrees C). However, some L/sub D/ improvement reappears for temperatures higher than 650 degrees C which is probably correlated with an enhancement of the phosphorus gettering. >

Rapid thermal annealing (RTA) was carried out on phosphosilicate glass (PSG) or phosphorus doped-spin-on glass (SOG) films deposited on silicon substrate in the typical processing temperature range of 800-1000 degrees C, to form n+p junctions. The sheet resistance, the total and active phosphorous profiles, and the minority carrier diffusion length using the surface photovoltage technique (SPV) have been measured on the processed samples. The results were compared to those obtained by conventional thermal annealing. It is shown that RTA is effective to achieve convenables sheet resistances and dopant profiles for solar cells in addition to an improvement in the silicon bulk properties. >

In this paper, the authors describe their work on a new solar cells fabrication process, based on the use of rapid thermal diffusion (RTD) from spin-on techniques, laser assisted treatments to get selective emitter structures and screen-printing. The homogeneous lightly doped emitter is first made by rapid thermal diffusion from a P-doped spin-on glass (SOG) film. Laser overdoping of contact regions follows, to form the selective emitter structure, by writing the grid pattern using a laser beam. Finally, screen-printing is used to obtain the contacts; proper solutions have been developed for optical realignment to the laser pattern, with a resolution of about 10 microns. The authors have prepared several batches of small area solar cells, made by using these processes separately, with the aim of studying the influence of the main laser and dopant parameters on solar cell performances. A further step has been to use all the processes together. Large area device preparation is in progress.

Simultaneous diffusion of phosphorus and aluminum by rapid thermal processing (RTP) in the order of one minute is used to realize emitter and back surface field in a single high temperature step, with controlled surface concentration of the dopant in order to obtain suitable front surface recombination velocities. Carefully controlling the mentioned parameter on industrial multicrystalline silicon (Polix(R) from Photowatt) lead to 16.7% efficient solar cells on a surface of 25 cm/sup 2/. All results are discussed in terms of photoconductivity decay and quantum efficiency analysis.

The authors present a new way of realising a selective emitter, using the simultaneous etching and hydrogenation properties of the ECR-H/sub 2/ plasma (electron cyclotron resonance hydrogen plasma). The impact of the H/sub 2/-plasma on multicrystalline silicon (POLIX/sup TM/) is studied in terms of bulk lifetime. It is shown that during the hydrogenation step, the ECR-plasma etches back the emitter surface at a rate of about 100 nm/hour. Besides, on sheet resistance mappings, they have observed that the etch rate depends on grain orientation. The etch-back is used to form the selective emitter during the hydrogenation process. Solar cells were realised using the screen-printed contacts as a mask against the plasma effect. The short circuit current can gain more than 1 mA/cm/sub 2/, the gain coming from the whole spectral range, this due to the less recombinating surface and the hydrogenated bulk material.

We have investigated the effects of simultaneous diffusion of phosphorus and aluminum in crystalline silicon on the minority carrier diffusion length as measured by the surface photovoltage technique. The diffusion is carried out by using a tungsten halogen lamp furnace (rapid thermal processing). We have shown that more than 100% bulk diffusion length improvement can be achieved in both float zone and Czochralski silicon material. The different contributions to this enhancement are discussed.

The minority carrier diffusion length in polycrystalline silicon has been strongly improved by using several gettering processes. These processes include different surface treatments followed by conventional thermal annealing (CTA) performed at temperatures between 800 and 950 °C. The n+p structures with a back lapped surface exhibit a maximum increase of the diffusion length from 35 to 140 μm for 45 min annealing duration at temperatures of 900 and 950 °C. The realization of a back surface field (BSF) on the lapped surface by aluminum deposition followed by a CTA cycle at 950 °C, with slow cooling rate (2 °C/min) induces a strong additional gettering, resulting in the increase of the minority carrier diffusion length up to 350%.