Publications (11)10.49 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: In this work secondary ion mass spectrometry (SIMS), variable angle spectroscopy ellipsometry (VASE) and atomic force microscopy (AFM) are used to investigate the structure, composition and morphology of multilayer SRON films. Three/four SRON sequential layers were deposited on silicon wafers by PECVD and silicon, nitrogen and oxygen content was varied by changing the N2O/SiH4 ratio. The total thickness of the resulting SRON stack is about 50nm. SIMS analyses of NCs+, OCs+, SiCs+, in MCs+ methodology are performed by a Cameca SC-ultra instrument. Depth profiles are obtained at 500eV of primary beam impact energy with sample rotation. An approximate method to obtain silicon concentration is used. Total layer thickness are obtained from both SIMS and VASE measurements. In addition, we compare the thickness of the single layers obtained from VASE with the SIMS depth profiles. A detailed analysis of films morphology is obtained by AFM. The SRON stack is sputtered by SIMS until a certain layer is exposed, which is then analyzed by AFM. The sputtered layers are then etched in HF solution to better resolve the exposed nano-crystals.
- [Show abstract] [Hide abstract] ABSTRACT: Recent results on the photoluminescence properties of silicon nanocrystals embedded in silicon oxide are reviewed and discussed. The attention is focused on Si nanocrystals produced by high-temperature annealing of silicon rich oxide layers deposited by plasma-enhanced chemical vapor deposition. The influence of deposition parameters and layer thickness is analyzed in detail. The nanocrystal size can be roughly controlled by means of Si content and annealing temperature and time. Unfortunately, a technique for independently fine tuning the emission efficiency and the size is still lacking; thus, only middle size nanocrystals have high emission efficiency. Interestingly, the layer thickness affects the nucleation and growth kinetics so changing the luminescence efficiency.
- [Show abstract] [Hide abstract] ABSTRACT: Silicon-rich-oxide (SRO) layers and silicon nano-crystals (Si-nc) have been gaining par-ticular attention for their optoelectronic properties. Analytical techniques as secondary ion mass spectrometry (SIMS), photo-electron spectroscopy (XPS), variable angle spectroscopy ellipsometry (VASE) and atomic force microscopy (AFM) were considered in this work as helpful ways to obtain the required characterization of these materials. SRO different films were deposited on Si wafers by plasma enhanced chemical vapor deposition (PECVD) and varying the ratio between SiH 4 , N 2 O and NH 3 . Then they were analyzed by SIMS and XPS, which combine the chemical physical ana-lytical techniques requested to provide quantitative and accurate results. Besides the high preci-sion of SIMS profiles, the accuracy of the data in SRO is marked as a difficult task, because of different matrices in different films. Therefore a fit equation for silicon SIMS depth profiles quanti-fication in SRO is proposed. The physic-chemical data were related to VASE measurements. Furthermore the structural properties of silicon nano-crystals were investigated by AFM. The de-veloped methodology confirms undoubtedly the Si-nc growth.
- [Show abstract] [Hide abstract] ABSTRACT: The characteristics of silicon-nitride films deposited with plasma-enhanced chemical vapour deposition (PECVD) can vary not only in composition, but also in terms of physical properties. An important parameter in the fabrication of micro-electro-mechanical systems (MEMS) devices is the control and tailoring of the film stress. In fact, silicon-nitride film stress can vary from tensile (up to 800 MPa) to compressive (−500 MPa), depending on the PECVD deposition conditions (e.g. plasma pressure, plasma frequency and power). In this work, we have investigated the role of frequency mixing on the resulting film structure and stress. The layers were prepared with a commercial PECVD deposition chamber, keeping all deposition parameters constant except the ratio between low (380 kHz) and high (13.56 MHz) frequency. Film stress values were compared with compositional and chemical data from X-ray photoemission spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements. These two techniques are complementary. The comparison between quantified SIMS depth profiles and the XPS HF etch-back method shows a good agreement in nitrogen profile behaviour. In addition, XPS analyses have provided a suitable chemical characterisation of the different growth processes. We demonstrate that this analytical approach is really effective for the physico-chemical characterisation of PECVD grown silicon nitride. Copyright
- [Show abstract] [Hide abstract] ABSTRACT: We study the effect on a LED of a controlled insertion of N in Si oxide containing Si nanocrystals. Nitrogen lowers the electronic potential barrier, thus increasing the carrier injection. Electroluminescence spectroscopy suggests that both electron and hole injection can be observed
- [Show abstract] [Hide abstract] ABSTRACT: A Fabry-Perot optical microcavity based on liquid crystal infiltration integrated in a waveguide has been designed and fabricated. Careful optimization of the cavity geometry allows designing a device with a simulated resonance peak transmission of 95% with a linewidth of about 1.7nm. Based on this simulation, a first prototype has been fabricated and tested.
- [Show abstract] [Hide abstract] ABSTRACT: This paper reports on Si<sub>3</sub>N<sub>4</sub>/SiO<sub>2</sub> multilayer waveguides to increase the optical confinement factor and, as consequence, to reduce optical losses.
- [Show abstract] [Hide abstract] ABSTRACT: Si3N4/SiO2 waveguides have been fabricated by low pressure chemical vapor deposition within a complementary metal-oxide-semiconductor fabrication pilot line. Propagation losses for different waveguide geometries (channel and rib loaded) have been measured in the near infrared as a function of polarization, waveguide width, and light wavelength. A maximum thickness of single Si3N4 of 250 nm is allowed by the large stress between Si3N4 and SiO2. This small thickness turns into significant propagation losses at 1544 nm of about 4.5 dB/cm because of the poor optical mode confinement factor. Strain release and control is possible by using multilayer waveguides by alternating Si3N4 and SiO2 layers. In this way, propagation losses of about 1.5 dB/cm have been demonstrated thanks to an improved optical mode confinement factor and the good quality of the interfaces in the waveguide.
- [Show abstract] [Hide abstract] ABSTRACT: In view of the integration within Si-based optical devices, LPCVD (low-pressure chemical vapor deposition) thin-film Si3N4 waveguides have been fabricated on a Si substrate within a CMOS fabrication pilot-line. Different structures (channel, rib and strip-loaded) were designed, fabricated and characterized both optically and structurally to optimize waveguide performances. Geometry, sidewall as well as layer roughness of the waveguides have been investigated by scanning electron microscopy and atomic force microscopy. Optical guided modes have been observed and propagation loss measurements at 632.8 and 780 nm have been performed by using the cut-back technique, the insertion loss technique and scattered light collection. The channel waveguides have shown propagation losses of about 0.1–0.2 dB/cm. Differences between geometries and lithographic processes have been discussed. Polarization dependence of propagation losses has been investigated too.Optical guided modes have also been measured in the near-infrared range (at 1544 nm), where propagation losses are about 4.5–5 dB/cm, quite larger with respect to the visible, because of the poorer confinement factor of the optical modes.
- [Show abstract] [Hide abstract] ABSTRACT: Complementary metal-oxide-semiconductor-compatible tunable Fabry-Perot microcavities filled with liquid crystals (LCs) were realized and studied in the near-infrared region. The microcavities were produced by chip bonding technique, which allows one to infill LC between two [SiO2/Si]n lambda/4 (lambda = 1.5 mum) Dielectric Bragg Reflectors separated by 950 nm thick SiO2 posts. The Dielectric Bragg reflectors were realized on Si or SiO2 substrates Liquid crystals with positive and negative dielectric anisotropy were used, i.e. MerckE7 (Deltaε=13.8) and Merck-6608 LC (Deltaε=-4.2). Mirror-integrated electrodes allow an external bias to induce an electrical field and to tune the LC properties and, hence, the microcavity resonance. Electric-field-induced shifts of the second-order cavity modes of ~120 nm and ~50 nm were obtained for Merck-E7 and Merck-6608 LC, with driving potentials of 5 V and 10 V, respectively. The transmittance at the cavity resonance is typically in the order of 10%. Simulation of cavities allows to identify surface roughness of the Dielectric-Bragg-Reflectors as the major origin of the transmission losses. The switching behavior of microcavities filled with E7 were studied as function of applied fields. Both switch-on ton and switch-off toff times were measured and were found to be lower than 5 ms.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper we present preliminary results for a PECVD based omnidirectional waveguide in silicon technology that consists of alternating SiO 2 and Si thin films. The light guiding is based on a reflector cladding, which reflects light at any angle or polarisation back into the core.
Fondazione Bruno Kessler
Trient, Trentino-Alto Adige, Italy
- Microtechnologies Laboratory (MTLab)