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Experimental evidences and microscopic modelling of the mechanism of B diffusion in Si and Ge are given. In both the lattices B migrates by the mediation of self-interstitials (Is). In Si, B diffusion occurs mainly through the formation of a BI0 complex, after interactions of BS- with I0 or with I++ in intrinsic condition or high hole densities, respectively, followed by a proper charge exchange. A small contribution of the BI- complex is visible only under n-type doping, when BS- and I0 bind nonetheless the pairing of B with the n-dopants. Also in Ge, the B diffusion mechanism has been fixed, even if to a lower extent, revealing the need of self-interstitials to start the B motion. We evidenced the occurrence of the proton radiation enhanced diffusion (RED) and of the transient enhanced diffusion (TED) of B, modeling both the cases with the central role of Is.

Positron annihilation spectroscopy (PAS) in Doppler broadening mode was used to study the vacancy profile of crystalline Si after He and B implantation and subsequent annealing. In the He-implanted samples two different void layers were observed, one consisting of large voids at the projected range of He and another containing “nanovoids” slightly larger than divacancies at roughly halfway between Rp of He and the surface. The nanovoid layer was shown to be absent from samples co-implanted with B, implying that interstitials created during B implantation get trapped in the nanovoids and fill them, thus hindering interstitial-mediated B diffusion.

Introduction to photovoltaics and potential applications of group IV nanostructures J. Valenta, S. Mirabella Dielectric function and spectrophotometry: from bulk to nanostructures C. Summonte Ab initio calculations of the electronic and optical properties of group IV semiconductor nanostructures embedded in different matrices R. Guerra, S. Ossicini Silicon nanoclusters embedded in dielectric matrices: nucleation, growth, crystallization, defects D. Hiller Excited-state relaxation in group IV nanocrystals investigated using optical methods F. Trojanek, P. Maly, I. Pelant Carrier multiplication in isolated and interacting silicon nanocrystals I. Marri, M. Govoni, S. Ossicini The introduction of majority carriers into group IV nanocrystals D. Konig Electrical transport in Si-based nanostructured superlattices B. Garrido, S. Hernandes, Y. Berencen, J. Lopez-Vidrier, J. M. Ramirez, O. Blazquez, B. Mundet Ge nanostructures for harvesting and detection of light A. Terrasi, S. Cosentino, I. Crupi, S. Mirabella Application of surface-engineered silicon nanocrystals with quantum confinement and carbon nanomaterials in solar cells V. Svrcek, D. Mariotti Prototype PV cells with Si nanoclusters S. Janz, P. Loper, M. Schnabel

The structural, electrical and optical properties of crystalline Si co-doped with Er and O by molecular beam epitaxy (MBE) and annealed at 900°C for 1 h have been investigated in detail. We observed clear constraints to the Er content that can be incorporated in a good quality single crystal. Moreover, we show that the O:Er ratio represents the main parameter in determining the properties of this system: Er electrical and optical activation increases with O:Er ratio until a saturation regime is achieved for a ratio higher than 6–8. We attribute this saturation regime to the full O coordinated first shell surrounding Er atoms in the Si host after the annealing at 900°C. In contrast, the most intense room temperature photoluminescence (PL) peak is obtained in samples having an O:Er ratio ∼2, for which PL temperature quenching is strongly reduced. Moreover, we investigated by X-ray photoelectron spectroscopy (XPS) the Er mobility for different temperatures and observed its penetration into the Si bulk from an Er/Si surface only after the annealing at 900°C. These phenomena are investigated in detail and discussed.

This paper investigates the morphological evolution of hydrogenated amorphous silicon layers obtained by plasma enhanced chemical vapor deposition at different H dilutions in the regime close to the formation of the nanocrystalline phase. The role of hydrogen in the transition from the amorphous to the crystalline phase is investigated by accurate structural and chemical characterization, from the early stages of nucleation, where the nuclei present size slightly larger than the critical nucleus, i.e., about 0.8 nm in radius, up to the formation of crystalline grains larger than 30 nm in radius. A correlation between the structural characteristics of such crystalline phase and the bonding mechanism of Si with H through multiple hydrides, such as Si-H2 and Si-H3 is found, particularly the tri-hydrides are found to be directly correlated to the shape and the size of the nanocrystallites present in the films. The multiple hydrides are found to play a role also in the electrical characteristics of p-i-n a-Si:H solar cells whose intrinsic layer is realized in the above H dilution conditions. An explanation of the experimental data in terms of the different bonding mechanism of H in the Si matrix is provided.

We report on high responsivity, broadband metal/insulator/semiconductor photodetectors with amorphous Ge quantum dots (a-Ge QDs) as the active absorbers embedded in a silicon dioxide matrix. Spectral responsivities between 1-4 A/W are achieved in the 500-900 nm wavelength range with internal quantum efficiencies (IQEs) as high as ∼700%. We investigate the role of a-Ge QDs in the photocurrent generation and explain the high IQE as a result of transport mechanisms via photoexcited QDs. These results suggest that a-Ge QDs are promising for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget. © 2011 American Institute of Physics.

Producción Científica, We present an extended model for B clustering in crystalline or in preamorphized Si and with validity under conditions below and above the equilibrium solid solubility limit of B in Si. This model includes boron-interstitial clusters (BICs) with BnIm configurations—complexes with n B atoms and m Si interstitials—larger (n > 4), and eventually more stable, than those included in previous models. In crystalline Si, the formation and dissolution pathways into large BICs configurations require high B concentration and depend on the flux of Si interstitials. In the presence of high Si interstitial flux, large BICs with a relatively large number of interstitials (m ≥ n) are formed, dissolving under relatively low thermal budgets. On the contrary, for low Si interstitial flux large BICs with few interstitials (m ≪ n) can form, which are more stable than small BICs, and whose complete dissolution requires very intense thermal budgets. We have also investigated the kinetics of large BICs in preamorphized Si, both experimentally and theoretically. B was implanted at a high-dose into preamorphized Si, and the B precipitation was studied by transmission electron microscopy and by sheet resistance and Hall measurement techniques. A simplified model for B clustering and redistribution in amorphous Si is proposed, including the experimental value for the B diffusivity in amorphous Si and the energetics of BICs. Our model suggests that B2, B3I, B4I and B4I2 clusters are the most energetically favored configurations, with relative abundance depending on B concentration. After recrystallization, thermal anneals up to 1100 °C evidence that BICs evolve under very low flux of Si interstitials under the particular experimental conditions considered. Simulations indicate that for very high B concentrations and low Si interstitial flux a significant fraction of the initial small BICs evolves into larger and very stable BIC configurations that survive even after intense thermal budgets, as confirmed by energy filtered transmission electron microscopy analyses. The correlation between simulations and Hall measurements on these samples suggest that hole mobility is significantly degraded by the presence of a high concentration of BICs., Ministerio de Economía, Industria y Competitividad (Project TEC2008-06069), Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA011A09)

The double sign anomaly of the Hall coefficient has been studied in p -doped and n -doped hydrogenated amorphous silicon grown by plasma enhanced chemical vapor deposition and annealed up to 500 °C. Dark conductivity as a function of temperature has been measured, pointing out a conduction mechanism mostly through the extended states. Anomalous Hall effect has been observed only in the as-deposited n -doped film, disappearing after annealing at 500 °C, while p -doped samples exhibit normal Hall effect. When Hall anomaly is present, a larger optical band gap and a greater Raman peak associated with Si-H bond are measured in comparison with the cases of normal Hall effect. The Hall anomaly will be related to the hydrogen content and implication on photovoltaic applications will be discussed. © 2010 American Institute of Physics.

Evolution of electrically active dose, sheet resistance and hole mobility has been investigated for high B concentration profiles in pre-amorphized Si. For this purpose, Hall measurements combined with atomistic simulations have been performed. An apparent anomalous behavior has been observed for the evolution of the active dose and the sheet resistance, in contrast to opposite trend evolutions reported previously. Our results indicate that this anomalous behavior is due to large variations in hole mobility with active dopant concentration, much larger than that associated to the classical dependence of hole mobility with carrier concentration. Simulations suggest that hole mobility is significantly degraded by the presence of a large concentration of boron-interstitial clusters, indicating the existence of an additional scattering mechanism.

Positron annihilation spectroscopy (PAS) in the Doppler broadening mode is used to study the effects of He and B implantation, and subsequent annealing on the vacancy profile of crystalline Si. The existence of two void layers, one consisting of large voids at the projected range (Rp) of He and another containing 'nanovoids' slightly larger than divacancies at roughly halfway between Rp of He and the surface is shown for samples implanted with He. Furthermore, the same nanovoid layer is shown to be absent from samples co-implanted with B, implying that interstitials created during B implantation get trapped in the nanovoids and fill them, thus indicating that the nanovoid layer is behind the hindrance of B diffusion.

Boron, as the main p-type dopant in Si, has been extensively investigated both experimentally and theoretically in order to understand its diffusion mechanisms for modelling and optimization of advanced devices. Crystalline Si matrix was mostly studied, but quite recently increased interest emerged on the behaviour of B in amorphous Si. In this work we present our recent progress in understanding these fundamental processes. Extensive investigation about the room temperature diffusion of B induced by the analyzing beam during secondary ion mass spectrometry, allowed to give information about diffusion mechanism of B both in crystalline and in amorphous phase. Moreover this put the basis for accurate measurements that allowed to investigate the key parameters describing the B diffusion in different equilibrium conditions, i.e. in wide ranges of temperature and doping level. On this basis, a comprehensive, experimentally based, atomistic model for B diffusion has been assessed, advancing and clarifying in a coherent picture the wide existing literature, including the interactions among B and self-interstitial in different charge states. Also the amorphous phase shows a complex B diffusion mechanism, far from being Fick-like. By means of simulation modelling of extensive diffusion data, produced in a wide range of temperatures, times and B concentrations, we have demonstrated that B promotes the formation of dangling bonds and it interacts with them in order to diffuse. Peculiar physical features, such as diffusion shape and transient diffusion, are correctly described by the model. (C) 2008 Elsevier B.V. All rights reserved.

We demonstrate that He can be a powerful tool to control B diffusion both in crystalline (c-Si) and preamorphized Si (PA-Si). By means of positron annihilation spectroscopy (PAS), we showed in He-implanted c-Si the formation after annealing of large open-volume defects at the implant projected range R-p of He (voids) and of smaller vacancy-type defects toward the surface (nanovoids). In particular, these nanovoids locally suppress the amount of self-interstitials (Is) generated by B implantation, as verified by PAS, eventually reducing B diffusion and leading to a boxlike shape of the B-implanted profile. On the other hand, for B implantation in PA-Si, the authors demonstrated that if He-induced voids are formed between the end-of-range (EOR) defects and the surface, they act as a diffusion barrier for Is coming from the EOR defects. Indeed, this barrier strongly reduces diffusion of B placed in proximity of the surface. (C) 2008 American Vacuum Society.

The authors have investigated ultrashallow p(+)/n-junction formation by solid-phase epitaxy, by using x-ray absorption near-edge spectroscopy (XANES) measurements at the B K edge. The authors demonstrate that B clustering occurs during the very early stages of annealing-induced Si recrystallization, i.e., when B is still in the amorphous matrix. After complete regrowth, the local structure around B remains the same as in the amorphous phase, implying that B clusters are transferred to the crystalline structure. The XANES structure are assigned to B-B sp(2) bonds that are present in B clusters with two or more B atoms. Boron clustering and diffusion are further investigated by means of concentration profile analysis of ad hoc amorphous on insulator structures that evidences a clear concentration threshold for clustering and a concentration dependent B diffusion. (C) 2008 American Vacuum Society.

"The formation and evolution of F-induced nanobubbles in Si was investigated. Si samples were preamorphized, implanted with F, and partially regrown by solid phase epitaxy (SPE). It is shown that nanobubbles are formed already in the amorphous side of partially regrown samples and are then incorporated in crystalline Si during SPE. The bubbles are interpreted as the result of the diffusion and coalescence of F atoms and dangling bonds already in the amorphous matrix. During high temperature annealing after SPE, F outdiffuses; correspondingly, the bubbles partially dissolve and transform from spherical- to cylinder-shaped bubbles. (C) 2008 American Institute of Physics."

The formation and growth of nanovoids in a C-doped Si layer after He+ implantation and thermal annealing are reported. A structure consisting of 240 nm of Si, 20 nm of Si doped with C at 0.8 at. %, and 240 nm of Si cap was realized by molecular beam epitaxy onto a (100) Si Czochralsky substrate. Three sets of samples were implanted with He+ at 30 keV and different doses of 8x10(15), 3x10(16), and 5x10(16) cm(-2) and subsequently annealed at 800 degrees C in N-2 atmosphere. Cross-section transmission electron microscopy was used to determine the void size and location. The tensile strain of the C-doped layer was measured by high-resolution x-ray diffraction. Our studies report the double role of C in the formation and evolution of nanovoids. After the low dose implantation, the C-doped layer still shows tensile strain due to substitutional C, and voids are localized only within this layer. At higher implantation doses, all the C atoms have been displaced from substitutional sites. No more strain is present in the C-doped layer and the presence of large cavities in its neighborhood is strongly inhibited. This work shows how localized strain in epitaxial films can be effectively used to drive nanovoid formation and evolution. (C) 2008 American Institute of Physics.

Kinetic Monte Carlo simulations have been used to investigate mechanisms for boron clustering in crystalline and preamorphized Si. We have extended previous boron-interstitial cluster models to include larger and more stable complexes in order to reproduce boron cluster evolution at very high boron concentrations. We have investigated the stoichiometry of boron-interstitial clusters resulting from low temperature recrystallization of preamorphized layers. We have performed a dedicated experiment based on boron implanted into preamorphized Si with end-of-range defects placed far enough from the boron profile to avoid the interaction between end-of-range defects and resulting boron-interstitial clusters after recrystallization. Hall measurements on active B dose combined with a systematic analysis performed by Kinetic Monte Carlo simulations indicate that initial boron-interstitial clusters after recrystallization should not contain a high amount of Si interstitials. Otherwise, boron deactivation and subsequent reactivation will occur faster than experimentally observed. The present results suggest B-3 and B-3 I clusters as the most probable configurations after recrystallization. (C) 2008 Elsevier B.V. All rights reserved.

In this work we investigate the promising properties of F in helping the B confinement in pre-amorphized Si, looking into the physical mechanisms acting. We studied also the effect of F on the electrical activity of B-doped junctions in pre-amorphized Si. The carrier dose, measured by four-point probe and Hall effect techniques, lowers because of F, with respect to the sample implanted only with B. To explain the measured B deactivation we employed scanning probe microscopy that allowed to verify a significant F-donor behaviour. Our results clarifies that the physical reason for the lost of holes dose in junctions co-implanted with B and F is not due to a chemical interaction between dopants and F, but simply to a dopant compensation effect.

In this paper we present a systematic study on the formation of He ion implantation induced nanovoids in Si and how they influence the self-interstitial (Is) supersaturation, thus affecting the diffusion and electrical activation of implanted boron in crystalline silicon. We implanted He ions into (100)-oriented Si wafers, with doses ranging from 5x10(15) to 8x10(16) He ions/cm(2) and energies ranging from 25 to 110 keV. Then, we implanted B ions (12 keV, 5x10(14) ions/cm(2)). All samples were annealed at 800 degrees C in N-2 atmosphere. We demonstrated the role of nanovoids in reducing B diffusion already at the first stages of postimplantation annealing. The effect has been attributed to the Is trapping by the nanovoids that forces B to assume a boxlike profile. Moreover, we studied the nanovoid distribution as a function of He-implanted dose and energy, demonstrating, by means of Cu gettering experiments, the beneficial effect of increasing dose or decreasing energy of He implantation on the B diffusion and electrical activation. In fact, if the nanovoid density is high in the proximity of implanted B, implantation-related damage can annihilate at the internal dangling bonds of nanovoids, thus consuming the nanovoid layer. The potential of He coimplantation as a method for controlling point-defect distributions in crystalline Si is presented and critically discussed.

We investigated the effect of F on the electrical activity of B-doped junctions in preamorphized Si. It is shown that while the carrier dose introduced by B is reduced in the presence of F, no indication of B-F complexes formation can be found and B maintains its full substitutionality. Investigations on F-enriched crystalline Si demonstrated and quantified the n-type doping of F. These results clarify that the loss of holes in junctions coimplanted with B and F is not due to a chemical interaction between B and F, but simply to a dopant compensation effect. (c) 2007 American Institute of Physics.

In this work we demonstrate that He co-implantation can be a powerful tool to control B diffusion in crystalline silicon (c-Si). In particular, the He induced damage leads to the formation of a distribution of nanovoids near the surface that locally suppress the amount of self-interstitials (Is) generated by further B implantation. Thus, B diffusion is reduced and the B implanted profile assumes a box-like shape. In particular, we analyze the microscopic mechanisms leading to the implanted B -nanovoids interaction, demonstrating that the Is injected from the B implanted region annihilate at nanovoids while eroding the nanovoid front layer. By means of a simulation of B diffusion, we will demonstrate that the consequent non-uniform interstitial supersaturation within the sample determines the peculiar B box-like shape, which is particularly appealing for device fabrication.

A definitive method to prevent undesired phenomena related to B implantation in crystalline Si is still lacking. In fact, B undergoes enhanced diffusion, clustering and electrical deactivation as a consequence of interaction with implantation related damage. In this work we investigated the effect of He and B co-implantation in Si on point-defect population. We implanted Si wafers with B 12 keV, 5 × 10 14 ions/cm 2 and/or He 25–80 keV, 0.5–3 × 10 16 ions/cm 2 . By means of B diffusion and Cu gettering experiments, we studied the effectiveness of He induced nanovoids on controlling self-interstitials generated by implantation. We demonstrated that nanovoids strongly affect B diffusion, producing a B box-like shape, and that their efficiency increases with increasing He fluence. Moreover, this beneficial effect is still present increasing the annealing temperature from 700 to 1000 °C, leading to a reduction of B clustering, while maintaining a strong confinement of the implanted B profile.

Light scattering from ZnO nanorods (NR) is investigated, modeled, and applied to a solar cell. ZnO NR (120-1300 nm long, 280-60 nm large), grown by low-cost chemical bath deposition at 90 degrees C, exhibit diffused-to-total transmitted light as high as 70% and 30% in the 400 and 1000 nm wavelength range, respectively. Data and scattering simulation show that ZnO NR length plays a crucial role in light diffusion effect. A transparent ZnO NR film grown on glass and placed on top of a 1 mu m thick c-Si solar cell is shown to enhance the light-current conversion efficiency for wavelengths longer than 600 nm. (C) 2015 AIP Publishing LLC.

Fluorine is known to have a beneficial role for the B diffusion reduction in preamorphized Si, and is promising for the realization of ultra-shallow junctions. Thus, we studied the F incorporation in Si during the solid phase epitaxy (SPE) process, pointing out the effects of the implanted F energy and fluence and the, role played by the possible presence of dopants. The incorporation of fluorine proceeds by F segregation at the amorphous-crystalline interface, with a kinetics driven by the SPE rate. In fact, the quicker the SPE rate, the higher is the F fluence retained. Moreover, we demonstrated that F incorporated in Si layers does not appreciably affect the Is emission from spatially separated end-of-range (EOR) defects. The modification, induced by the presence of F, of the point defect density (Is and Vs) was also studied by means of B and Sb spike layers, used as local markers for Is and Vs, respectively. We showed that F is not only able to completely suppress the boron transient enhanced diffusion (TED), but can enhance the antimony diffusion. These experimental data demonstrate the ability of F in inducing an Is undersaturation or a Vs supersaturation, ruling out the hypothesis of a chemical bonding between F and the dopants. These results improve the engineering of F-enriched Si, for the realization of ultra-shallow junctions. (c) 2006 Elsevier B.V. All rights reserved.

While it is known that F modifies dopant diffusion in crystalline Si, the physical mechanisms behind this process are still unclear. In this work we report experimental studies about the F control of the point defect density in preamorphized Si layers. These studies put the basis for the understanding of the F behavior and for the realization of ultra-shallow junctions. We first investigated the F incorporation process during the solid phase epitaxy (SPE) of amorphous Si layers. We elucidated the role of the SPE temperature on the F incorporation and suggested a new route towards a F profile engineering. Moreover, we explained the role of F in modifying the point defect population (self-interstitials, Is, and vacancies, Vs), employing B and Sb spike layers as markers for Is and Vs, respectively. We clearly showed that F decreases the B diffusion while enhances the Sb one, pointing out the capacity to induce an Is undersaturation or a Vs supersaturation. These data rule out the hypothesis of a chemical bonding between F and the dopants. Such F ability in modifying the Is/Vs density resulted to be a transient effect, because strictly correlated with the presence of F in the Si samples, which decreases with the annealing time. In addition, we evidenced that even if F is spatially separated from B, i.e., localized between shallow-implanted B and the end-of-range (EOR) region, it still suppresses the enhancement of B diffusivity, due to the EOR defects dissolution. These studies, besides improving the current understanding of the physical mechanisms by which F influences the dopant diffusion in Si, could be helpful for the realization of ultra-shallow junctions for the future metal-oxide-semiconductor devices. (c) 2006 American Institute of Physics.

We studied the strain induced in a silicon lattice by the presence of boron clusters formed by the interaction of high concentration (2 x 10(20) at cm(-3)) substitutional B with Si interstitials produced by ion implantation. We found that the clustered immobile B induces a significant amount of strain in the host lattice. By analysing the dissolution behaviour of boron clusters after prolonged annealing, we found that the strain linearly decreases as the amount of clustered B decreases, evidencing a constant lattice expansion Delta V per clustered B atom of (3.7 +/- 0.6) angstrom(3), independently of the annealing temperature and time. By performing model potential calculations of Delta V on selected boron clusters, we concluded that these clusters can be structurally more complex than those commonly assumed or hypothesized so far.

We studied the effect of implanted fluorine on B-doped silicon formed by Si preamorphization, solid phase epitaxy (SPE) regrowth and post-SPE thermal treatments. We showed that the fluorine is an efficient diffusion inhibitor for boron, revealing the crucial importance of F implementation in the future generation devices. In samples doped with B we observed an anomalous F accumulation at the dopant implantation peak. Since the physical mechanisms driving these phenomena are not yet well understood, we investigated the effect of the presence of B and/or As on the F incorporation during the SPE process at 580 degrees C. By using As coimplantation (thus modifying the SPE rate) we demonstrated that the above mentioned increased F incorporation is due to a kinetic effect, related to the SPE rate modification by doping, while a F-B chemical bonding is refused. These data shade new light upon the mechanism responsible for B diffusion reduction by F. (c) 2006 American Vacuum Society

The beneficial effects of F implantation on the modification of extended defects in Si have been studied. Preamorphized Si samples were implanted with F (75 keV, 6x10(15) F/cm(2)) and regrown by solid phase epitaxy (SPE) at 700 degrees C. The formation, just after SPE, of a band of bubbles overlapping the F enriched region has been evidenced, clearly demonstrating the formation of F-vacancy (V) complexes with determined stoichiometry. Moreover, the authors demonstrate that these F-V complexes inhibit the formation of extended defects, acting as efficient traps for Si interstitials. These results represent a promising route toward point defects engineering in microelectronic application. (c) 2006 American Institute of Physics.

Recently we have demonstrated that substitutional boron in crystalline silicon can migrate for long distances even at room temperature (RT) and below during secondary ion mass spectrometry (SIMS) profiling. The phenomenon is suppressed after amorphization or by cooling the sample. The above data force to reconsider the observations obtained in the last decades by SIMS in light of possible long-range migration artifacts. Here we show that the use of oxygen flooding (OF) during the analysis enhances the injection of self-interstitials (I) responsible for the migration of B, producing profiles that are more broadened and less accurate than in ultrahigh vacuum. On the other hand, by properly controlling OF, we have obtained new insights on the mechanisms of B diffusion and interaction with intrinsic traps at RT. Moreover, by cooling the sample the migration of B is suppressed even while using OF, allowing measurements of boron deltas in c-Si of unprecedented level of accuracy and sensitivity. Finally, we have clarified the role of the migration phenomena on the profiling of ultra low energy B implants for ultra shallow junctions. (c) 2006 American Vacuum Society.

In order to meet the technological requirements for the next generations of p-n junctions, highly promising methods consist of B and C ultra-low energy co-implantation in Ge pre-amorphized Si. We investigated the B diffusion and the activation phenomena occurring during post-annealing of ultra-shallow junctions (USJ) obtained by spike annealing Si samples pre-amorphized by 20 keV Ge and co-implanted with C at 4 keV and B at 500 eV. Isochronal (60 s) post-annealing processes were performed in inert atmosphere (N-2) by rapid thermal annealing (RTA) in the 500-1050 degrees C temperature range. We show that, contrary to what reported in the literature about C-free USJ, no B diffusion occurs up to 900 degrees C, and further B clustering is completely suppressed over the whole investigated temperature range. Moreover we observed an increase of the sheet resistance by increasing the temperature up to 900 degrees C followed by a subsequent decrease, that can be easily interpreted on the basis of B diffusion and segregation in native SiO2 and B cluster dissolution. Finally, we show that C significantly reduces up to two orders of magnitude the diffusion coefficient of B, that in our experiments is present in highly extrinsic conditions. (c) 2006 Elsevier B.V. All rights reserved.

This work reports on the lattice strain induced by small B clusters in Si produced by He irradiation of an epitaxial layer uniformly doped with substitutional B. By means of high resolution X-ray diffraction measurements and nuclear reaction analysis, lattice strain profiles and B lattice location of the sample before and after He irradiation were extracted, respectively. We found that, as a consequence of He irradiation, all B atoms form B-B pairs, and the tensile strain status of the as-grown B-doped layer lowers by a factor of about 2. Moreover, the volume lattice expansion Delta V per clustered B atom was found to be (-(10.0 +/- 0.6) angstrom(3)). This negative value of AV is very different from the positive one (+(3.7 +/- 0.6) angstrom(3)) found for B clusters created as a consequence of the B interaction with self-interstitials produced by Si implantation and subsequent annealing [G. Bisognin, D. De Salvador, E. Napolitani, A. Carnera, E. Bruno, S. Mirabella, F. Priolo, A. Mattoni, Semicond. Sci. Technol. 21 (2006) L41]. The opposite sign of this volume lattice expansion suggests that a strong correlation exists between the atomistic structures associated with these two types of complexes and the lattice strain that they induce in the Si lattice. (c) 2006 Elsevier B.V. All rights reserved.

Scanning capacitance microscopy (SCM) was carried out in the angle beveling configuration on B doped, very narrow quantum wells (QWs) of Si0.75Ge0.25 layers strained between Si films. The majority carrier concentration profiles were calculated from the SCM raw data measured on QWs with a minimum width of 5 nm, doped with different B concentrations ranging from 2x10(16) to 6x10(18) cm(-3). The equilibrium carrier distribution in the heterostructures has been calculated by different simulation approaches, which will be discussed. Moreover, the effect of the biased tip-sample interaction was studied by accurate simulations of the dC/dV vs V characteristics for different positions of the tip moving on the beveled sample surface. The agreement between the experimental and simulated SCM profiles is very good. Thus, a spatial SCM resolution of at least 5 nm was demonstrated on angle beveled samples, not only in terms of signal sensitivity, but also in terms of quantitative majority carrier profiling.

The injection of Si self-interstitial atoms during dry oxidation at 815 degreesC of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe/Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2/SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.

We show that B clusters, produced by self-interstitial interaction with substitutional B in crystalline Si, dissolve under annealing according to two distinct paths with very different characteristic times. The two regimes generally coexist, but while the faster dissolution path is predominant for clusters formed at low B concentration (1x10(19) B/cm(3)), the slower one is characteristic of clusters formed above the solubility limit and dominates the dissolution process at high B concentration (2x10(20) B/cm(3)). The activation energies of both processes are characterized and discussed. It is showed that the faster path can be connected to mobile B direct emission from small clusters, while the slower path is demonstrated not to be self-interstitial limited and it is probably related to a more complex cluster dissolution process.

We demonstrate that substitutional B in silicon can migrate even at room temperature and below, stimulated by a high interstitial flux. Once mobile B is formed, it migrates for long distances with a diffusivity >5 x 10(-13) cm(2)/s, until it assumes an immobile configuration with a migration length independent of the temperature. This phenomenon is present during secondary ion mass spectrometry (SIMS) analyses of B profiles, altering the profile during the analysis itself. These results shed new light on all the data based on SIMS analyses and reported in literature in the last decades.

In this work the silicon self-interstitial (I) diffusion in trap-containing molecular beam epitaxy Si layers is investigated. The I’s are produced by Si ion implantation, and the I supersaturation is reported as a function of the depth and the annealing time. These data are discussed on the basis of two alternative models proposed in literature (“effective diffusivity” model and “filling trap” model). This analysis demonstrates that the second model is more appropriate to describe the proposed phenomenology, since it explains both the increase of the I penetration depth as a function of the implant dose and the very rapid change of the supersaturation versus time. Moreover, the proposed model takes account for the I recombination at the surface.

In this work, we have investigated the strain induced in a Si crystal by Boron-interstitial clusters (BICs). BICs were formed by Si implantation and subsequent annealing of two Si samples, grown by molecular beam epitaxy (MBE), containing thin buried layers doped with different B concentrations (10 19 and 10 20 at./cm 3 ). By B chemical profile diffusion analysis the doses of Si self-interstitials (Is) and Boron atoms trapped in the BICs were extracted. The B/I stoichiometric ratio is about 1 for the low B concentration and about 3.5 for the high B concentration sample. High-resolution X-ray diffraction (HRXRD) analyses provided a measure of the strain profile. While in the low B concentration sample, no appreciable strain was detected after BICs formation, at the higher B concentration, we found that the tensile strain present in the as-grown B doped layer changes to a strong compressive strain as a consequence of BIC formation. For this kind of clusters, the mean volume expansion with respect to the Si matrix is 29 ± 6 A 3 for each B atom trapped in the BICs.

The two dimensional (2D) diffusion of self- interstitials (I) in crystalline Si, both at room temperature and at 800 degreesC, has been studied by quantitative SCM measurements. The 2D I emission from a I source laterally confined down to sub-micron dimensions, obtained by low-energy implantation through a patterned oxide mask, has been observed. At room temperature, I diffusion was monitored by measuring the electrical deactivation of B corresponding to the diffusing interstitial tail and it was demonstrated that this deactivation is due to compensating levels introduced by defects in the Si bandgap. At 800 degreesC I diffusion was monitored by measuring the transient enhanced diffusion of B spikes due to interstitial supersaturation produced during the annealing. In both cases, a dependence of the I depth- penetration on the original source size has been shown for mesoscopic window opening; (from 0.5 to 3 mum).

In this work the diffusion of ion-beam-injected self-interstitials (Is) and their interaction with impurities in crystalline Si are presented. In particular, the I penetration into a molecular beam epitaxy grown Si structure was studied by means of diffusion effects induced on B spikes, analyzed by a developed simulation code. Trapping effects at sample-surface and bulk are evidenced and modeled. The B marker approach was extended to the two-dimensional (2D) I-diffusion occurring as a consequence of ion implantation through a sub-micron dimension patterned oxide mask. I-source size effects on the I penetration have been found and modeled, quantitatively describing the 2D I-diffusion. The I-substitutional carbon interactions have been also studied, showing the C ability to effectively retain Is. The I-trapping mechanism was quantitatively studied by the simulation code, showing that one I is able to deactivate about two C traps by means of I-trapping and C-clustering reactions. This C property was used to control the ion-implantation induced damage and, consequently, to completely suppress B transient enhanced diffusion. Finally, the interaction between I and B leading to the B agglomeration into small B–I clusters (BICs) has been experimentally investigated. BICs dissolution kinetics was studied at different temperatures, directly using experimental concentration profiles and an opportunely developed B-diffusion simulation code. The activation energy for BICs dissolution and the BICs stoichiometry are extracted and given.

Scanning capacitance microscopy (SCM) has been performed both in cross-sectional and in angle-beveling configurations on ultranarrow B spikes with a full width at half-maximum smaller than the SCM probe diameter. The dependence of the SCM response on the magnification factor has been studied, demonstrating an improvement both in terms of spatial resolution and sensitivity by angle-beveling sample preparation. The range of applicability of the direct inversion approach for the quantification of SCM profiles on ultranarrow B spikes has been assessed for high doping spikes thicker than 3 nm and measured on bevel. Two-dimensional simulations allowed the reproduction of all the main features of the experimental SCM profiles.

Scanning capacitance microscopy (SCM) has been applied to monitor the two-dimensional (2D) diffusion of Si self- interstitials ( I ). A sub-micron laterally confined source has been generated by Si self-implantation through a sub-micron oxide mask. The structure was grown by molecular beam epitaxy on (0 0 1) Si, with three spikes of B at different depths used as markers for the interstitial concentration. The measured 2D SCM maps have been accurately quantified to 2D carrier concentration profiles, yielding quantitative information on the B diffusion induced by the I flux. The I supersaturation inside the wafer was monitored by the broadening and the consequent peak concentration lowering of the boron spikes. We show that the I depth- penetration strongly depends on the original source lateral size. Moreover, lateral diffusion of I has been observed, being independent of the source size.

The recent activity performed on scanning capacitance microscopy is reviewed. The influence of surface states on measurements is described and reproducibility and sensitivity issues are addressed. Some examples of applications on devices and process characterisation and interpretation are shown. The application of the method to SiC is also discussed.

In this work a rate equations model describing the interstitials (I) diffusion in a trap containing medium is presented. The model takes into account the interstitial injection by implantation and annealing and the surface evaporation. We found an analytical approximated solution of the model which allows clarifying the interplay between the parameters involved and a simple comparison with experimental data obtained by the analysis of boron delta doping arrays broadening. The calculations allow to demonstrate that the I injected into the bulk and toward the surface at the end of the I clusters dissolution does not depend on the detailed time evolution of the I clusters, but only on the total amount of I produced by the implantation. The fitting of the experimental data allows to easily quantifying important physical parameters such as the I evaporation rate at the surface and the density of intrinsic interstitial traps. Applications of the model are shown in the case of MBE materials intentionally doped with substitutional C. The model successfully predicts the TED reduction by MBE intrinsic I-traps and allows to estimate the average composition of Interstitial-Carbon clusters.

The two-dimensional (2D) diffusion of Si self-interstitials (I) from a submicron laterally confined source has been investigated in detail. High-resolution scanning capacitance microscopy was used for quantitative measurements of the B transient enhanced diffusion induced by the I flux generated by a low-energy Si implantation through a submicron dimension oxide mask. We show that the I depth penetration strongly depends on the original lateral size of the source. The 2D I diffusion has been well described by a 2D rate equations model, using the same physical parameters valid for one-dimensional diffusion.

A method for completely suppressing the transient enhanced diffusion (TED) of boron implanted in preamorphized silicon is demonstrated. Boron is implanted in a molecular beam epitaxy (MBE) grown silicon sample that has been previously amorphized by silicon implantation. The sample is then annealed in order to epitaxially regrow the amorphous layer and electrically activate the dopant. The back-flow of silicon interstitials released by the preamorphization end-of-range (EOR) damage is completely trapped by a carbon-rich silicon layer interposed by MBE between the damage and the implanted boron. No appreciable TED is observed in the samples up to complete dissolution of the EOR damage, and complete electrical activation is obtained. The method might be considered for the realization of ultra shallow junctions for the far future complementary metal-oxide semiconductor technology nodes.

The structural, electrical, and optical properties of crystalline Si codoped with Er and O by molecular beam epitaxy (MBE) have been investigated in detail. Si:Er:O layers (∼250 nm thick) have been grown by MBE, realizing uniform dopant concentrations in the range 8×1018–1.5×1020 cm−3 for Er and up to 5×1020 cm−3 for O. The O:Er ratio was varied between 0 and ∼20. Samples have been subsequently annealed at 900 °C for 1 h. We observed that clear constraints to the Er and O contents exist in order to incorporate them in a good quality single crystal. We also found that the O:Er ratio represents the main parameter in determining the properties of this system. For instance, Er is observed to behave as a donor in MBE grown samples and the donor concentration increases with the O:Er ratio until a saturation regime is achieved for a ratio higher than 6–8. All the samples emit light at 1.54 μm and similar behavior is also found for the optical activation of the Er ions. The thermal process usually increases the n...

Thin film Si:O alloys have been grown by plasma enhanced chemical vapor deposition, as intrinsic or highly doped (1 to 5 at. % of B or P dopant) layers. UV-visible/near-infrared spectroscopy revealed a great dependence of the absorption coefficient and of the optical gap (Eg) on the dopant type and concentration, as Eg decreases from 2.1 to 1.9 eV, for the intrinsic or highly p-doped sample, respectively. Thermal annealing up to 400 °C induces a huge H out-diffusion which causes a dramatic absorption increase and a reduction of Eg, down to less than 1.8 eV. A prototypal solar cell has been fabricated using a 400 nm thick, p-i-n structure made of Si:O alloy embedded within flat transparent conductive oxides. Preliminary electrical analyses show a photovoltaic (PV) effect with an open circuit voltage of 0.75 V and a spectral conversion efficiency blue-shifted in comparison to a-Si:H based cell, as expected since the higher Eg in Si:O alloy. These data are presented and discussed, suggesting Si:O alloy as promising material for PV device fabrication. © 2013 AIP Publishing LLC.

The authors have investigated ultrashallow p(+)/n-junction formation by solid-phase epitaxy, by using x-ray absorption near-edge spectroscopy measurements on the B K edge. A clear fingerprint of B-B clusters is detected in the spectra. The authors demonstrate that B clustering occurs during the very early stages of annealing-induced Si recrystallization, i.e., when B is still in an amorphous matrix. After complete regrowth the local structure around B remains the same as in the amorphous phase, implying that B clusters are transferred to the crystalline structure. (c) 2006 American Institute of Physics.

The effect of interstitial trapping by surface nanovoids, induced by He ion implantation in crystalline Si, is described. The difference with respect to the effects induced by the deep void layer is evidenced and discussed. Interstitial trapping is investigated by studying the diffusion and the electrical activation of shallow boron implanted in Si. B and He ion implantations were performed on Czochralski bulk and silicon-on-insulator samples in order to isolate the void surface region from the deep void layer. A remarkable reduction of B diffusion is recorded near half the projected range (R-p) of He implantation, which leads to a boxlike shape in the distribution of mobile and electrically active B. Surface nanovoids (2-3 nm in size) cause the observed B diffusivity reduction through an enhanced recombination of self-interstitials. Moreover, these surface nanovoids do not hinder the B electrical activation, being the electrically active B dose comparable for the He implanted and the He-free samples. This peculiar effect of He coimplantation at about half the R-p could be used as an efficient interstitial trapping in defect engineering during Si based device processing.

The lattice location of B in Si has been investigated by channelling analyses using nuclear reactions (650 keV proton beam, B-11(p,alpha)Be-8). The formation at room temperature of a specific, small B complex in presence of an excess of point defects has been inferred. In particular, B implanted in Si or B substitutional dissolved in Si and irradiated with proton beam form a unique B complex with B atoms not randomly located. The angular scans along the < 100 > and < 110 > axes are compatible with B-B pairs aligned along the < 100 > axis. The thermal annealing in the 200-950 degrees C range of the B complexes, analyzed by lattice location and carrier concentration measurements, depends on the residual defect density in the lattice. The B complexes dissolve at low temperature if no excess of Si self-interstitials (Is) exists or they evolve into large B clusters and then dissolve at high temperature if Is supersaturation holds.