Antulio Tarazona

Hot-wire polysilicon waveguides with low deposition temperature

We fabricated and measured the optical loss of polysilicon waveguides deposited using hot-wire chemical vapor deposition at a temperature of 240°C. A polysilicon film 220 nm thick was deposited on top of a 2000 nm thick plasma-enhanced chemical vapor deposition silicon dioxide layer. The crystalline volume fraction of the polysilicon film was measured by Raman spectroscopy to be 91%. The optical propagation losses of 400, 500, and 600 nm waveguides were measured to be 16.9, 15.9, and 13.5 dB/cm, respectively, for transverse electric mode at the wavelength of 1550 nm. Scattering loss is expected to be the major contributor to the propagation loss.

Large Gauge Factor of Hot Wire Chemical Vapour Deposition In-Situ Boron Doped Polycrystalline Silicon

Polysilicon piezoresistors with a large longitudinal gauge factor (GF) of 44 have been achieved using in-situ boron doped hot-wire chemical vapour deposition (HWCVD). This GF is a consequence of a high quality p-type doped polysilicon with a crystal volume of 97% and an average grain size of 150 nm, estimated using Raman spectroscopy and atomic force microscopy (AFM) respectively. The measured minimum Hooge factor associated to the 1/f noise of the polysilicon piezoresistors is 1.4 × 10−3. These results indicate that HWCVD polysilicon is a suitable piezoresistive material for micro-electro-mechanical systems (MEMS) applications.

Laser annealing of low temperature deposited silicon waveguides

We report the fabrication of low temperature deposited polysilicon waveguides using a laser annealing process. Micro-Raman and XRD measurements reveal the quasi-single crystal-like quality of the material, which exhibits low optical losses of 5.13 dB/cm.

Characterization of epitaxial heavily-doped silicon regions formed by HWCVD using Micro-Raman and Micro-Photoluminescence Spectroscopy

We report on the characterization of heavily boron doped epitaxial silicon regions grown in a hot-wire chemical vapor deposition tool, using micro-Raman and photoluminescence spectroscopy. In particular, the use of this approach for emitter fabrication in an interdigitated back contact silicon solar cell is studied, by analyzing its suitability concerning selective growth, uniformity, anneal time, and luminescent defects. We show that by reducing the silane flow rate, both the required postanneal time and intensity of defect luminescence are reduced. Furthermore, we show that selective area growth does not affect either the quality of the films or the sharpness of the resulting lateral doping profile. The uniformity of the doping is shown to be better than that achieved using laser doping.

HWCVD a-Si:H interlayer slope waveguide coupler for multilayer silicon photonics platform

We present an interlayer slope waveguide, designed to guide light from one level to another level in a multilayer silicon photonics platform. The waveguide is fabricated using HWCVD a-Si:H at 350oC. Measured loss of 0.5 dB/slope was obtained at a wavelength of 1550 nm and for TE mode polarization.

Laser annealed low temperature deposited polysilicon waveguides for nonlinear photonics

The intrinsic properties of silicon (Si) make it an excellent material for integrated photonics devices with small footprints [1]. To date, most of the reported devices have been based on crystalline silicon (c-Si), but this material suffers from difficult integration with electronic layers due to fabrication constraints. Subsequently, there has been growing interest in alternative forms of Si, such as hydrogenated amorphous silicon (a-Si:H), silicon nitride (SiN) and polysilicon (poly-Si) [2]. Among these materials, only poly-Si has the potential to exhibit both optical and electronic properties that are equivalent to c-Si. However, to achieve good material quality, poly-Si is typically deposited at temperatures higher than 900°C, rendering it incompatible with most CMOS fabrication processes. Thus there is a growing drive to develop new techniques to deposit poly-Si at low temperatures (<450°C) [2], but so far the optical losses in these materials have been high, limiting its use in all-optical systems employing nonlinear optical processing. In this work, we report the fabrication and characterisation of laser annealed, low temperature deposited silicon waveguides with low optical losses. Our results represent the first demonstration of nonlinear propagation in a poly-Si waveguide suitable for integration.

Laser writing of polycrystalline Si ridge waveguides

Polycrystalline silicon (poly-Si) has attracted significant interest in the area of silicon photonics because of its potential for combining good optical transmission, electronic functionality and low fabrication cost, which makes it an attractive material for commercial applications [1]. In addition, it was shown recently that by laser processing of amorphous Si (a-Si) it is possible to obtain very large grain poly-Si [2] resulting in a material with superior optical and electronic performance.

Broadband 2D diamond grating couplers with variable pitch

We present the design, simulation and measurements of broadband gratings couplers with a variable grating pitch. The measured 3 dB bandwidth was over 110 nm. The gratings employ diamond-shaped sub-wavelength grating (SWG) structures for dispersion control and a varying pitch along the transmission axis.

Low temperature silicon nitride waveguides for multilayer platforms

Several 3D multilayer silicon photonics platforms have been proposed to provide densely integrated structures for complex integrated circuits. Amongst these platforms, great interest has been given to the inclusion of silicon nitride layers to achieve low propagation losses due to their capacity of providing tight optical confinement with low scattering losses in a wide spectral range. However, none of the proposed platforms have demonstrated the integration of active devices. The problem is that typically low loss silicon nitride layers have been fabricated with LPCVD which involves high processing temperatures (<1000 ºC) that affect metallisation and doping processes that are sensitive to temperatures above 400ºC. As a result, we have investigated ammonia-free PECVD and HWCVD processes to obtain high quality silicon nitride films with reduced hydrogen content at low temperatures. Several deposition recipes were defined through a design of experiments methodology in which different combinations of deposition parameters were tested to optimise the quality and the losses of the deposited layers. The physical, chemical and optical properties of the deposited materials were characterised using different techniques including ellipsometry, SEM, FTIR, AFM and the waveguide loss cut-back method. Silicon nitride layers with hydrogen content between 10-20%, losses below 10dB/cm and high material quality were obtained with the ammonia-free recipe. Similarly, it was demonstrated that HWCVD has the potential to fabricate waveguides with low losses due to its capacity of yielding hydrogen contents <10% and roughness <1.5nm.

Junction Formation With HWCVD and TCAD Model of an Epitaxial Back-Contact Solar Cell

In this paper, we present morphological and electrical characteristics of a junction formed of Si p-type films deposited on an n-type silicon wafer using a hot wire chemical vapor deposition (HWCVD) tool. We describe the fabrication process and study the influence of diborane flow and postprocess annealing in improving junction characteristics. Our morphological studies undertaken using atomic force microscopy show that the initial deposition suffered from voids rather than being a uniform film; however, this improves significantly under our annealing treatment. The improvement in morphology was observed in the electrical characteristics, with estimated Voc doubling and rectification of the junction improving by several orders of magnitude. Fitting of the current-voltage curves to a two-diode model showed that increasing the diborane flow in the process helps reduce the saturation current and ideality factors, while increasing the shunt resistance. Electrochemical capacitance-voltage (ECV) and quasi-steady-state photoconductance measurements are used to characterize the deposited films further. A solar cell device with a silicon epitaxy emitter is modeled using industry-standard 3-D modeling tools and input parameters from experimental data, and the impact of defects is studied. A potential efficiency approaching 25% is shown to be feasible for an optimized device.