Papers by francesco priolo
Journal of Physics-condensed Matter, 2003
CMOS circuitry dominates the current semiconductor market due to the astonishing power of silicon... more CMOS circuitry dominates the current semiconductor market due to the astonishing power of silicon electronic integration technology. In contrast to the dominance of silicon in electronics, photonics utilises a diversity of materials for emitting, guiding, modulating and detecting light. In the last ten years a big research effort was aimed to render Si an optical active material so that it can be turned from an electronic material to a photonic material. For some the future of Si-based photonic lays in "hybrid" solutions, for others the utilisation of more photonic functions by silicon itself. During the last two years many breakthroughs in the field have appeared. In this paper we will review what we believe the most important: optical gain in silicon nanostructures.
Physical Review B, 2004
Sensitization of Er emission by Si nanoclusters (Si-nc) is investigated with pulsed and continuou... more Sensitization of Er emission by Si nanoclusters (Si-nc) is investigated with pulsed and continuous optical pumping, in and off resonance with excited states of Er 3+ ion. We show that under high-power pulsed pumping, the excitation process is limited by the finite energy transfer time from Si-nc to Er 3+ ions. By comparison between pulsed and steady-state excitation, the concentration of sensitizers and average number of Er 3+ ions coupled to a single nanocluster are independently determined in an experiment. The results clarify conditions needed for efficient sensitization of SiO 2 : Er by Si-nc.
Silicon-Based Light-Emitting Devices: Properties and Applications of Crystalline, Amorphous and Er-Doped Nanoclusters
IEEE Journal of Selected Topics in Quantum Electronics, 2006
In this paper, we summarize the results of an extensive investigation on the properties of MOS-ty... more In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light-emitting devices based on silicon nanostructures. The performances of crystalline, amorphous, and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 $mu$ m. Amorphous nanoclusters are more conductive than the crystalline counterpart. In contrast, nonradiative processes seem to be more efficient for amorphous clusters resulting in a lower quantum efficiency. Erbium doping results in the presence of an intense EL at 1.54 $mu$ m with a concomitant disappearance of the 900-nm emission. This suggests that under electrical pumping Er is excited through an efficient energy transfer from the silicon clusters which hence become dark. We have identified an Auger de-excitation of Er with trapped carriers as the main process competing with radiative emission and limiting EL efficiency. This process is particularly severe in presence of unbalanced carrier injection (electrons versus holes) and can be controlled in properly designed structures. These data are presented and their implications are discussed.
Journal of Applied Physics, 1995
We have studied the effect of erbium-impurity interactions on the 1.54 pm luminescence of EJ?' in... more We have studied the effect of erbium-impurity interactions on the 1.54 pm luminescence of EJ?' in crystalline Si. Float-zone and Czochralski-grown (100) oriented Si wafers were implanted with Er at a total dose of -1 X 10'5/cm2. Some samples were also coimplanted with 0, C, and F to realize uniform concentrations (up to 102'/cm3) of these impurities in the Er-doped region. Samples were analyzed by photoluminescence spectroscopy (PL) and electron paramagnetic resonance (EPR). Deep-level transient spectroscopy (DLTS) was also performed on p-n diodes implanted with Er at a dose of 6XlO"/cmz and codoped with impurities at a constant concentration of 1X101s/cm3. It was found that impurity codoping reduces the temperature quenching of the PL yield and that this reduction is more marked when the impurity concentration is increased. An EPR spectrum of sharp, anisotropic, lines is obtained for the sample codoped with 102' O/cm3 but no clear EPR signal is observed without this codoping. The spectrum for the magnetic field B parallel to the [ 1001 direction is similar to that expected for Ersf in an approximately octahedral crystal field. DLTS analyses confirmed the formation of new Ers' sites in the presence of the codoping impurities. In particular, a reduction in the density of the deepest levels has been observed and an impurity+Er-related level at -0.15 eV below the conduction band has been identified. This level is present in Er+O-, ErfF-, and ErfC-doped Si samples while it is not observed in samples solely doped with Er or with the codoping impurity onIy. We suggest that this new level causes efficient excitation of Er through the recombination of e-h pairs bound to this level. Temperature quenching is ascribed to the thermalization of bound electrons to the conduction band. We show that the attainment of well-defined impurity-related luminescent Er centers is responsible for both the luminescence enhancement at low temperatures and for the reduction of the temperature quenching of the * huninescence. A quantitative model for the excitation and deexcitation processes of Er in Si is also proposed and shows good agreement with the experimental results. 0 1995 American Institute of Physics.
Atomic transport properties and electrical activation of ultra-low energy implanted boron in crystalline silicon
Materials Science in Semiconductor Processing, 1999
The growing importance of ultra-low energy implantation in Si processing imposes extensive charac... more The growing importance of ultra-low energy implantation in Si processing imposes extensive characterization and understanding of such a novel energy regime. In this paper we investigate the evolution of ultra-low energy B implants (0.25–1 keV) after post-implantation annealing, both in terms of atomic diffusion and electrical activation of the doping atoms. Transient enhanced diffusion (TED) of boron after annealing at
Defect production and annealing in ion-irradiated Si nanocrystals
Physical Review B, 2002
In this paper the formation and annihilation of defects produced in Si nanocrystals (nc) by ion-b... more In this paper the formation and annihilation of defects produced in Si nanocrystals (nc) by ion-beam irradiation are investigated in detail. The luminescence properties of Si nanocrystals embedded in a SiO2 matrix were used as a probe of the damaging effects generated by high-energy ion-beam irradiation. Samples have been irradiated with 2 MeV He+, Si+, Ge+, and Au+ ions at
Nature, 2000
We report measurements of stimulated emission and single pass light ampli®cation in Si nanocrysta... more We report measurements of stimulated emission and single pass light ampli®cation in Si nanocrystals obtained by ion implantation. We argue that population inversion involves Si@O interface states. Ó
Erbium-doped Si nanocrystals: optical properties and electroluminescent devices
Physica E-low-dimensional Systems & Nanostructures, 2003
... This will produce an additional saturation in the 1.54 μm curve of Fig. 5. ... Moreover, the ... more ... This will produce an additional saturation in the 1.54 μm curve of Fig. 5. ... Moreover, the 1540 nm PL intensity is enhanced by over an order of magnitude. Since the room temperature luminescence intensity of Er-doped Si nc is already two orders of magnitude higher than for Er ...
Journal of Modern Optics, 2002
We provide a systematic study on the linear and nonlinear optical properties of silicon nanocryst... more We provide a systematic study on the linear and nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma-enhanced chemical vapour deposition (PECVD). Linear optical properties, namely absorption, emission and refractive indices are reported. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility À …3 † of Si-nc are measured by the Z-scan method. Closed aperture Z-scan reveals a positive nonlinearity for all the samples. From the open aperture measurements, nonlinear absorption coe cients are evaluated and attributed to two-photon absorption. Absolute values of À …3 † are in the order of 10 ¡9 esu and show systematic correlation with the Si-nc size, due to quantum con®nement related e ects. A correlation has been made between À …3 † , nanocrystalline size, linear refractive index and optical band gap.
Journal of Applied Physics, 2002
Comprehensive studies on nonlinear refractive indices ͑n 2 ͒ of SiO 2 films containing Si nanocry... more Comprehensive studies on nonlinear refractive indices ͑n 2 ͒ of SiO 2 films containing Si nanocrystals and/or nanoclusters ͑SiO 2 : Si-ncs͒ are performed. The comparison of the nonlinear refractive indices with the electron spin resonance signals reveals that defect states play a major role in the large n 2 when the annealing temperature is low, i.e., when Si nanoclusters exist in films. On the other hand, when Si nanocrystals are grown by high-temperature annealing, the contribution of defect states becomes small and that of the quantized electronic states of Si nanocrystals becomes large. The present results demonstrate that both the defect states and the quantized electronic states should be taken into account to explain the origin of large n 2 of SiO 2 : Si-ncs and to optimize the structure to maximize n 2 .
Excitation and nonradiative deexcitation processes of Er3+ in crystalline Si
Physical Review B, 1998
... per la Fisica della Materia and Dipartimento di Fisica, Universita di Catania, Corso Italia 5... more ... per la Fisica della Materia and Dipartimento di Fisica, Universita di Catania, Corso Italia 57, I 95129 Catania, Italy ` Giorgia Franzo and Salvatore Coffa Istituto ... Chemical profiles were measured by secondary ion mass spectrometry SIMS using a CAMECA IMS 4 f instrument. ...
Physical Review B, 2003
Light-emitting silicon nanocrystals embedded in SiO 2 have been investigated by x-ray absorption ... more Light-emitting silicon nanocrystals embedded in SiO 2 have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding SiO 2 is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric SiO 2 . This region plays an active role in the light-emission process.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2002
Higher integration in semiconductor technology with the continuing downscaling of device dimensio... more Higher integration in semiconductor technology with the continuing downscaling of device dimensions into the sub-hundred nanometer range causes the need for ultra-shallow junctions [1]. Novel techniques are necessary to achieve abrupt and sharp profiles of dopants at high activation levels without significant diffusion of dopants. Two processes, low energy ion implantation and rapid thermal annealing (RTA), are currently the key processing steps for the formation of such ultra-shallow junctions .
Advanced Materials, 2007
Currently, electrical interconnections based on metal lines represent the most important limitati... more Currently, electrical interconnections based on metal lines represent the most important limitation on the performances of silicon-based microelectronic devices. The parasitic capacities generated at the metal/insulator/metal capacitors present in the complex multilevel metallization schemes actually used, the intrinsic resistivity of the metal lines, and the contact resistance at the metal/metal interfaces constitute the main contributions to the delay in the signal propagation. Recently, a reduction of the delay times was achieved by replacing the traditional metallization schemes based on Al and SiO 2 with new materials, such as copper-based alloys and low-dielectricconstant insulating layers, but as soon as the minimum feature size of the devices will be further reduced, the delay resulting from metal interconnections will again represent an unacceptable bottleneck for device performances. A definitive solution to this problem could be the use of optical interconnections for the transfer of information inside a chip or for chip-to-chip communications. To develop this strategy, siliconcompatible materials and devices able to generate, guide, amplify, switch, modulate, and detect light are needed. Recent major breakthroughs in this field have been the observation of optical gain in Si nanocrystals, the development of a Si Raman laser, the realization of a high-speed Si electro-optic modulator, and the observation of electroluminescence from ultrapure Si diodes and Si nanocrystal field-effect transistors. A primary requirement for the materials proposed for the above applications is compatibility with current Si technology. However, because Si is intrinsically unable to efficiently emit light, owing to its indirect bandgap, it is evident that the main limitation to the approach described above is the lack of an efficient silicon-based light source. Among the efforts of the scientific community to efficiently produce photons from silicon, the introduction of light-emitting impurities, such as erbium ions, has a leading role. A relevant advantage of this approach is that standard silicon technology can be used to introduce erbium as a dopant and to process the material. Furthermore, Er ions emit at 1.54 lm, which is a strategic wavelength for telecommunication because it corresponds to a minimum in the loss spectrum of the silica optical fibers. Incorporation of Er in crystalline silicon (c-Si) emerged as the first promising method to turn silicon into a luminescent material, but doping concentration was limited (ca. 1 × 10 18 cm -3 ) by the low solid solubility of Er. A co-implantation of Er and O allowed to limit Er segregation and precipitation, owing to the formation of Er-O complexes. However, at room temperature a relatively low luminescence efficiency was obtained as a result of the strong nonradiative processes competing with the radiative Er de-excitation in c-Si. More recently, it was shown that by using a SiO 2 matrix containing Er-doped Si nanoclusters, an intense room-temperature Er luminescence can be obtained. Indeed, it has been demonstrated that Si nanoclusters in presence of Er act as efficient sensitizers for the rare earth owing to the effective Er excitation cross section, which is more than two orders of magnitude higher compared with the Er resonant absorption of a photon. Optical gain from waveguides based on Er-doped Si nanoclusters has been also reported, and lightemitting devices have been fabricated. However, the optical gain that can be obtained from this system is critically dependent on its Si content, and it is limited by the confined carrier absorption resulting from the presence of Si nanoclusters. Even if gain can prevail over absorption through a careful balance of Er and Si concentrations, absorption could represent a limit for obtaining high gain values from Er-doped Si nanoclusters.
The excitation mechanism of rare-earth ions in silicon nanocrystals
Applied Physics A-materials Science & Processing, 1999
A detailed investigation on the excitation mechanisms of rare-earth (RE) ions introduced in Si na... more A detailed investigation on the excitation mechanisms of rare-earth (RE) ions introduced in Si nanocrystals (nc) is reported. Silicon nanocrystals were produced by high-dose 80-keV Si implantation in thermally grown SiO2 followed by 1100 °C annealing for 1 h. Subsequently some of the samples were implanted by 300-keV Er, Yb, Nd, or Tm at doses in the range 2×1012–3×1015 /cm2. The energy was chosen in such a way to locate the RE ions at the same depth where nanocrystals are. Finally an annealing at 900 °C for 5 min was performed in order to eliminate the implantation damage. These samples show intense room-temperature luminescence due to internal 4f shell transitions within the RE ions. For instance, luminescence at 1.54 μm and 0.98 μm is observed in Er-doped nc, at 0.98 μm in Yb-doped nc, at 0.92 μm in nc and two lines at 0.78 μm and 1.65 μm in Tm-doped nc. Furthermore, these signals are much more intense than those observed when RE ions are introduced in pure SiO2 in the absence of nanocrystals, demonstrating the important role of nanocrystals in efficiently exciting the REs. It is shown that the intense nc-related luminescence at around 0.85 μm decreases with increasing RE concentration and the energy is preferentially transferred from excitons in the nc to the RE ions which, subsequently, emit radiatively. The exact mechanism of energy transfer has been studied in detail by excitation spectroscopy measurements and time-resolved photoluminescence. On the basis of the obtained results a plausible phenomenological model for the energy transfer mechanism emerges. The pumping laser generates excitons within the Si nanocrystals. Excitons confined in the nc can either give their energy to an intrinsic luminescent center emitting at around 0.85 μm nor pass this energy to the RE 4f shell, thus exciting the ion. The shape of the luminescence spectra suggests that excited rare-earth ions are not incorporated within the nanocrystals and the energy is transferred at a distance while they are embedded within SiO2. Rare-earth excitation can quantitatively be described by an effective cross section σeff taking into account all the intermediate steps leading to excitation. We have directly measured σeff for Er in Si nc obtaining a value of ≈2×10−17 cm2. This value is much higher than the cross section for excitation through direct photon absorption (8×10−21 cm2) demonstrating that this process is extremely efficient. Furthermore, the non-radiative decay processes typically limiting rare-earth luminescence in Si (namely back-transfer and Auger) are demonstrated to be absent in Si nc further improving the overall efficiency of the process. These data are reported and their implications.
Electroluminescence of silicon nanocrystals in MOS structures
Applied Physics A-materials Science & Processing, 2002
We have studied the structural, electrical and optical properties of MOS devices, where the diele... more We have studied the structural, electrical and optical properties of MOS devices, where the dielectric layer consists of a substoichiometric SiOx (x<2) thin film deposited by plasma-enhanced chemical vapor deposition. After deposition the samples were annealed at high temperature (>1000 °C) to induce the separation of the Si and the SiO2 phases with the formation of Si nanocrystals embedded in the insulating matrix. We observed at room temperature a quite intense electroluminescence (EL) signal with a peak at ∼850 nm. The EL peak position is very similar to that observed in photoluminescence in the very same device, demonstrating that the observed EL is due to electron–hole recombination in the Si nanocrystals and not to defects. The effects of the Si concentration in the SiOx layer and of the annealing temperature on the electrical and optical properties of these devices are also reported and discussed. In particular, it is shown that by increasing the Si content in the SiOx layer the operating voltage of the device decreases and the total efficiency of emission increases. These data are reported and their implications discussed.
Nanotechnology, 2006
We report the results of a detailed study on the structural, electrical and optical properties of... more We report the results of a detailed study on the structural, electrical and optical properties of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature electroluminescence (EL), with the advantage of being formed at a temperature of 900 • C, while at least 1100 • C is needed for the formation of Si nanocrystals. Optical and electrical properties of amorphous Si nanocluster devices have been studied in the temperature range between 30 and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a maximum at around 60 K. The efficiency of these devices is comparable to that found in devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar working conditions (very high current densities and low applied voltages). Time resolved EL measurements demonstrate the presence of a short lifetime, only partially due to the occurrence of non-radiative phenomena, since the very small amorphous clusters formed at 900 • C are characterized by a short radiative lifetime. By forcing a current through the device a phenomenon of charge trapping in the Si nanostructures has been observed. Trapped charges affect luminescence through an Auger-type non-radiative recombination of excitons. Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is one of the main processes limiting luminescence efficiency. These data will be reported and the advantages and limitations of this approach will be discussed.
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Papers by francesco priolo