Silicon-rich Oxide Research Articles

UV enhancement of silicon solar cells using thin SRO films

A study of comparison of the electrical and optical characteristics of silicon solar cells (SC) with a layer of silicon oxide (SiO2) deposited by SILOX, and silicon solar cells covered with a silicon rich oxide (SRO) film obtained by LPCVD containing silicon nanoparticles (Si-nps) was made. To increase the density of nanoparticles and thus improve the red photoluminescence, the SRO films were annealed at 1100°C. Photoluminescence spectra and atomic force microscopy measurements of the silicon rich oxide films are presented and discussed, as well as current–voltage curves and spectral response of the fabricated solar cells. Measurement of the open circuit voltage and short circuit current of the SC under UV light illumination was realized. The results demonstrate that the red luminescence of these films with silicon nanoparticles, produces large enhancement of current and voltage, with improved performance in the UV range.

Silicon nanocrystals in an oxide matrix for thin film solar cells with 492 mV open circuit voltage

We have fabricated solar cells with layers of co-sputtered silicon and silicon dioxide. The diode structures were fabricated by sputtering alternating layers of SiO2 and silicon rich oxide onto quartz substrates with in-situ boron, for p-type, and phosphorus, for n-type, doping. After crystallization at 1100°C, isolated Si-nanocrystals are formed. The thin film layers containing these crystals act as n-type or p-type semiconductors as determined from CV measurements on MOS structures. The dark and illuminated I–Vs of the fabricated diodes show a rectifying behavior with an open circuit voltage of 492mV under a simulated 1.5AMD illumination. A circuit model is proposed to explain the observed I–V characteristics.

Thermal annealing effects on photoluminescence properties of carbon-doped silicon-rich oxide thin films implanted with erbium

Results are presented from the photoluminescence properties of C-doped Si-rich thin film oxides implanted with Er, as investigated for various postdeposition implantation and subsequent annealing and passivation conditions. In particular, it was found that the near-infrared Er luminescence intensity can be increased by up to a factor of ∼4 after a postdeposition anneal at temperatures of 300–1100 °C. The postdeposition annealing also resulted in an enhancement of the green-red (500–600 nm) PL band associated with the film matrix. Post-Er implantation passivation in an oxygen atmosphere resulted in a gradual reduction in intensity for both the Er and matrix PLs, and led eventually to a complete quenching of both PLs at the highest passivation temperature (900 °C). In contrast, hydrogen passivation increased the matrix PL intensity by a factor up to ∼2, but was found to have negligible effects on Er PL intensity over a wide range of passivation temperatures. Analysis of Er and matrix-related PL characteristics suggests that the matrix luminescence centers are most likely the sensitizers responsible for energy transfer to Er in C-doped silicon oxides. In this context, a discussion is presented of potential types of matrix-related luminescence centers present in such materials, along with the possible mechanisms leading to differences in Er excitation and deexcitation between the C-doped Si-rich oxide films analyzed herein and commonly reported Si-rich oxide materials containing Si nanocrystals.

Optical and Electrical Properties of Si-Based Multilayer Structures for Solar Cell Applications

Among the materials of interest in the fields of solar cells, silicon Rich silicon Oxide (SRSO) has proved convincing results. In order to benefit from the carrier confinement within the active material, a multilayered arrangement of SRSO alternated with an insulating matrix is preferred. SiO2 matrix has been used as a host matrix, but its limitations appear due to the poor electrical conductivity. Hence, SiNx has become an alternative choice for such matrices in the recent past. This work compares the structure and luminescence properties of SRSO/SiO2 and SRSO/SiNx multilayers and demonstrates the interest in replacing SiO2 sublayer by SiNx. Optical and electrical characterizations are made on these materials We eventually propose a promising type of multilayer structure with enhanced photoluminescence and electrical conductivity with a control over the thermal budget.

Electromagnetic modeling of waveguide amplifier based on Nd3+ Si-rich SiO2 layers by means of the ADE-FDTD method

By means of ADE-FDTD method, this paper investigates the electromagnetic modelling of a rib-loaded waveguide composed of a Nd3+ doped Silicon Rich Silicon Oxide active layer sandwiched between a SiO2 bottom cladding and a SiO2 rib. The Auxilliary Differential Equations are the rate equations which govern the levels populations. The Finite Difference Time Domain (FDTD) scheme is used to solve the space and time dependent Maxwell equations which describe the electromagnetic field in a copropagating scheme of both pumping (λpump = 488 nm) and signal (λsignal = 1064 nm) waves. Such systems are characterized by extremely different specific times such as the period of electromagnetic field ~ 10-15 s and the lifetimes of the electronic levels between ~ 10-10s and ~ 10-4 s. The time scaling method is used in addition to specific initial conditions in order to decrease the computational time. We show maps of the Poynting vector along the propagation direction as a function of the silicon nanograin (Si-ng) concentrations. A threshold value of 1024 Si-ng m-3 is extracted below which the pump wave can propagate so that a signal amplication is possible.

Atomic scale investigation of silicon nanowires and nanoclusters

In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers.

High Voltage Device Negative Bias Temperature Instability Improvement with Different Process Conditions

Drastically device dimension shrinkage and rigorous requirement in automotive era puts Negative Bias Temperature Instability (NBTI) at the forefront of reliability issue recently. The PMOS parametric degradation during negative bias high temperature aging can depend on many process variables of the manufacturing flow. A study was carried out to explore the process related dependencies for high voltage PMOS transistor and to increase the device robustness against NBTI stress. In this papers, the process impact on the NBTI degradation were discussed. This investigation work provides methods for significant suppression of the NBTI degradation with silicon rich oxide (SRO) inter layer dielectric (ILD) liner and two-step gate oxidation.

Multiple excitation of silicon nanoclusters during erbium sensitization process in silicon rich oxide host

Sensitization of erbium through silicon nanocluster (Si-nc) in silicon rich oxide host has been analyzed through a statistical approach. Our analysis shows that significant fraction of Si-ncs can experience multiple excitations during the Er lifecycle. The probability of Si-nc being excited at every alternate cycles of excitation increases from small fractions to percentage levels for incident flux levels above 1018/cm2 s. We show that, for typical values of Er and Si-nc incorporation, saturating effects in Er luminescence starts at flux levels much lower than that for Si-nc excitation. Occurrence of multiple excitation of Si-nc has been correlated with the deteriorating effects in Er sensitization at higher flux incidence.

(Invited) Sensitization of Erbium Photoluminescence in Silicon-Rich Silicon Dioxide - Current Status and Future Perspectives

not Available.

Determination of the energy states of the donor acceptor decay emission in silicon rich oxide prepared by low-pressure chemical vapor deposition

Room temperature cathodoluminescence and photoluminescence were used to study silicon rich oxide (SRO) films with 5.5% silicon excess. Intense blue and red luminescence emissions were found. A SRO film was deposited by low-pressure chemical vapor deposition and was annealed at 1100 °C by 3 h in a nitrogen ambient. The emission from the SRO films was modeled as being due to donor-acceptor-pair decay. Calculations have been made to obtain the first estimates of the donor and acceptor energy distributions in SRO films.

Effect of the Nd content on the structural and photoluminescence properties of silicon-rich silicon dioxide thin films

In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously exhibited PL from Si-np and Nd3+ demonstrating the efficient energy transfer between Si-np and Nd3+ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive quenching of the Nd3+ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments. Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd3+.

Optical properties of silicon rich oxides

AbstractThermally treated silicon rich oxides (SRO) used as starting material for the fabrication of silicon nanodots represent the basis of tunable bandgap nanostructured materials for optoelectronic and photonic applications. The optical modelization of such materials is of great interest, as it allows the simulation of reflectance and transmittance (R&T) spectra, which is a powerful non destructive tool in the determination of phase modifications (clustering, precipitation of new phases, crystallization) upon thermal treatments. In this paper, we study the optical properties of a variety of as‐deposited and furnace annealed SRO materials. The different phases are treated by means of the effective medium approximation. Upon annealing at low temperature, R&T spectra show the precipitation of amorphous silicon nanoparticles, while the crystallization occurring at temperatures higher than 1000 °C is also clearly identified, in agreement with structural results. The existing literature on the optical properties of the silicon nanocrystals is reviewed, with attention on the specificity of the compositional and structural characteristics of the involved material. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of Cobalt-Based Nanocrystal Layer in Silicon Dioxide for Nonvolatile Memory Applications

Cobalt silicide (CoSi) nanocrystal (NC) layer distributed within narrow spatial region is synthesized by thermal annealing of a sandwich structure comprised of a thin cobalt (Co) film sandwiched between two silicon-rich oxide (SiO(x)) layers. It is shown that the size of the CoSi NCs can be controlled by varying the Co film thickness, an increase in the size with increasing thickness. Capacitance-voltage (C-V) measurements on a test metal/oxide/semiconductor (MOS) structure with floating gate based on CoSi NCs of 3.8 nm in diameter and 1.4 x 10(12) cm2 in density are shown to have C-V characteristics suitable for nonvolatile memory applications, including a C-V memory window of about 9.5 V for sweep voltages between -15 V and +8, a retention time >10(8) s, and an endurance > 10(6) program/erase cycles.

Comparison of silicon nanocrystals embedded silicon oxide films by sputtering and PECVD

The material and optical properties of the silicon rich oxide (SRO) films prepared by PECVD and sputtering were comprehensively studied. The optical properties were found strongly depend on the material properties of the SRO films. The photocurrent of the photodiodes using PECVD deposited SRO was ~ 3 order higher than that prepared by the sputtering, while the leakage current of the later was much lower than the former, leading the light/dark current ratio of the sputtered photodiodes was higher than the PECVD prepared ones when the bias voltage exceeded ~ 1.6 V. The transmission electron microscopy and the X-ray photoelectron spectroscopy were used to investigate the variations of the constitutive Si nanocrystals and the oxidation states. After annealing, size of the nanocrystals decreased and the oxidation states changed, changing the optical properties of the photodiodes.

Erbium implanted silicon rich oxide thin films suitable for slot waveguides applications

Thin (50 nm) erbium implanted silicon rich oxide films suitable for slot waveguides applications have been produced and studied by means of optical spectroscopy and structural characterisation techniques. Comparison between different deposition techniques in terms of light emitting properties of erbium ions is presented. Special attention is given to the efficiency improvement of the energy transfer from silicon nanoclusters to erbium ions where the type of annealing treatment is proven to be of crucial importance.

Photoelectric Properties of MOS-like Structures with Twofold SRO Films

The optical properties of silicon rich oxide (SRO) have been deeply studied because, between other reasons, they emit an intense photoluminescence (PL) from visible to the near infrared range when excited with UV light. MOS-like structures with SRO film as the active layer have shown an enhanced conductivity under different illumination conditions. In this paper, MOS-like structures with double SRO layer were fabricated in order to have a barrier to isolate the silicon substrate from the active SRO layer. Results show that all structures have a higher current when light shines on them than that obtained under dark conditions. A possible application of this photo-effect can be used to increase the response of photodetectors and silicon solar cells.

Silicon Nanocavity Based Light Sources

ABSTRACTWe develop Si-based nano-photonic devices for the control of light at the nano-scales. We design high quality (Q) factor photonic crystal nanobeam cavities for a variety of Si compatible materials with low index, such as silicon rich oxide and silicon nitride, all with Q > 9,000 and small mode volumes. We apply these cavity designs to active materials such as Sinanocrystal doped silicon oxide and Er doped silicon nitride. By placing emitters in these cavities, we demonstrate that the cavity enhances emission processes. We show that the free carrier absorption process is greatly enhanced in the nanobeam cavities at both room and cryogenic temperatures. In addition, we demonstrate that nanobeam cavities made of Er-doped amorphous silicon nitride have enhanced absorption and gain characteristics compared to earlier designs that included silicon in the cavity. Because of the reduced losses, we observe linewidth narrowing and material transparency at both room temperature and cryogenic temperatures.

Assessment of the composition of Silicon-Rich Oxide films for photovoltaic applications by optical techniques

Abstract The deposition of sub-stoichiometric silicon rich oxide (SRO) is the first step to obtain well ordered silicon Quantum Dots (QDs) in a dielectric matrix. This structure is used also for third generation photovoltaic devices operating in a tandem architecture. A precise control and assessment of the stoichiometry of these films is crucial to tune the electrical and optical properties of the device. In this paper we discuss two optical techniques to assess the composition of such films and we compare their results.

Photoluminescence of Er-doped silicon-rich oxide thin films with high Al concentrations

Er-doped silicon-rich oxide (SRO) thin films co-doped with Al in high concentrations were prepared by sputtering. Some films were deposited using a substrate heater (150 °C<Td<235 °C). Films deposited without using substrate heating were annealed to 700 °C. The photoluminescence (PL) of most of the former films was greater than the PL of the latter films. Excitation wavelength dependence (EWD) of Er ion emission presents variations as the O content decreases and the Al content increases. The dependence of the Er ion 980 nm peak PL with respect to the Er ion 1525 nm peak PL indicates that the first emission depends less on energy transfer upconversion (ETU) processes as the O content decreases and the Al content increases. Broadband excitable Er3+ infrared (IR) emission with less loss due to ETU processes is important for applications in photonics.

Cathodoluminescence and photoluminescence comparative study of erbium-doped silicon-rich silicon oxide

We present a study on erbium (Er)-doped silicon (Si)-rich silicon oxide thin films grown by the magnetron cosputtering of three confocal cathodes according to the deposition temperature and the annealing treatment. It is shown that, through a careful tuning of both deposition and annealing temperatures, it is possible to engineer the fraction of agglomerated Si that may play the role of sensitizer toward Er ions. To investigate the different emitting centers present within the films according to the fraction of agglomerated Si, a cathodoluminescence experiment was made. We observe in all samples contributions from point-defect centers due to some oxygen vacancies and generally known as silicon-oxygen deficient centers (SiODC), at around 450–500 nm. The behavior of such contributions suggests the possible occurrence of an energy transfer from the SiODCs toward Er3+ ions. Photoluminescence experiments were carried out to characterize the energy transfer from Si nanoclusters toward Er3+ ions with a nonresonant wavelength (476 nm) that is unable to excite SiODCs and then exclude any role of these centers in the energy transfer process for the PL experiments. Accordingly, it is shown that structural differences have some effects on the optical properties that lead to better performance for high-temperature deposited material. This aspect is illustrated by the Er-PL efficiency that is found higher for 500°C-deposited, when compared to that for RT-deposited sample. Finally, it is shown that the Er-PL efficiency is gradually increasing as a function of the fraction of agglomerated silicon.