E. Terzini

Amorphous silicon waveguides and light modulators for integrated photonics realized by low-temperature plasma-enhanced chemical-vapor deposition.

A new amorphous silicon waveguide is realized by use of amorphous silicon carbon as cladding material. The structure is characterized both experimentally and theoretically, and its application for optical interconnections in photonic integrated circuits on silicon motherboards is proposed. The fabrication process is based on low-temperature (220 degrees C) plasma-enhanced chemical-vapor deposition and is compatible with standard microelectronic processes. Propagation losses of 1.8 dB/cm have been measured at the fiber-optic wavelength of 1.3 microm. A strong thermo-optic coefficient has been measured in this material at this wavelength and exploited for the realization of a light-intensity modulator based on a Fabry-Perot interferometer that is tunable by temperature.

Amorphous silicon-based guided-wave passive and active devices for silicon integrated optoelectronics

Waveguides and interferometric light amplitude modulators for application at the 1.3- and 1.55-/spl mu/m fiber communication wavelengths have been fabricated with thin-film hydrogenated amorphous silicon and its related alloys. The technique adopted for the thin-film growth is the plasma- enhanced chemical vapor deposition, which has been shown to give the lowest defect concentration in the film. Consequently the proposed waveguiding structures take advantage of the low optical absorption shown by a-Si:H at photon energies below the energy gap. In addition a good radiation confinement can be obtained thanks to the bandgap tailoring opportunity offered by this simple and inexpensive technology. In particular rib waveguides, based on a a-SiC:H/a-Si:H stack, have been realized on crystal silicon, showing low propagation losses. Recently, however, a new interest as low as 0.7 dB/cm. The same structure has been utilized for the fabrication of thermooptic Fabry-Perot modulators with switching times of 10 /spl mu/s. Modulators based on the alternative waveguiding configuration ZnO/a-Si:H, giving comparable results, are also presented.

Fast infrared light modulation in a-Si:H micro-devices for fiber-to-the-home applications

Abstract We have produced and measured the properties of a fast switching micro-optic device in a rib-like configuration working at the 1.3 and 1.55 μm fiber communication wavelengths for fiber-to-the-home applications. The core guiding layer is made of intrinsic hydrogenated amorphous silicon (a-Si:H) deposited by plasma enhanced chemical vapour deposition (PECVD) with absorption coefficients sufficiently small at the wavelength of interest. The signal modulation is performed exploiting the thermo-optic effect of thin film a-Si:H in a Fabry–Perot waveguide integrated interferometer. Switching times

a-Si:H/a-SiC:H waveguides and modulators for low-cost silicon-integrated optoelectronics

Abstract Starting from an a-Si:H/a-SiC:H stack deposited by glow discharge on a crystal silicon wafer, we have fabricated and measured the properties of rib waveguides suitable for infrared optical communication purposes. Propagation losses as small as 0.7 dB/cm have been measured. The same waveguiding structure has been utilised for the construction of Fabry–Perot interferometers. As the process is compatible with the standard microelectronic technologies, the integration of optical and electronic functions on the same chip becomes possible.

Changes of hydrogen evolution thermodynamics induced by He and H2 dilution in PECVD a-Si:H films: influence on thermal crystallization

Abstract Intrinsic and n-type amorphous silicon films were deposited by plasma-enhanced chemical vapour deposition on Qz (fused silica), crystalline silicon and aluminium substrates. Different substrate temperatures (200°C and 300°C) and 50% diluted SiH 4 in He or H 2 process gas were used to change hydrogen content and microstructure of deposited amorphous material. The hydrogen evolution thermodynamics of a-Si:H films was investigated using differential scanning calorimetry to obtain the entropy change and the activation energy of hydrogen evolution process. Crystallization of a-Si:H was obtained by an isothermal annealing performed at a pressure of 30 mTorr, at 650°C, using different annealing times (30–480 s). Different entropy variations are observed in the a-Si:H films. The hydrogen evolution affects the crystallization kinetics; in fact, crystallization was delayed in the samples with a greater disorder after hydrogen evolution.

Amorphous silicon waveguides and interferometers for low-cost silicon optoelectronics

The present work reports on our recent achievements in the exploitation of a simple technology for the fabrication of hydrogenated amorphous silicon (a-Si:H) based low-loss rib waveguides. In particular, waveguides with various widths have been fabricated out of an a-SiC:H/a-Si:H stack deposited by plasma enhanced chemical vapor deposition at the relatively low temperature of 220 degrees C. The ribs were defined by an anisotropic, CH4-based, reactive ion etching process. The devices have been subsequently characterized by cut-back technique. Even though a dependence of attenuation parameter on the waveguide width was observed, propagation losses as low as 0.7 dB/cm could be measured at λ=1.3 μm, in good agreement with he theoretical estimations based on the intrinsic absorption of the material. Starting from the same structure, a Fabry- Perot thermo optical modulator has been also fabricated and tested at the communication wavelength of 1.3 μm.

Thermo-optical modulation at /spl lambda/=1.5 μm in an /spl alpha/-SiC-/spl alpha/-Si-/spl alpha/-SiC planar guided-wave structure

A planar waveguide based on an amorphous silicon-amorphous silicon carbide heterostructure is proposed for the realization of passive and active optical components at the wavelengths /spl lambda/=1.3-1.5 /spl mu/m. The waveguide has been realized by low temperature plasma enhanced chemical vapor deposition and is compatible with the standard microelectronic technologies. Thermo-optical induced modulation at /spl lambda/=1.5 /spl mu/m is demonstrated in this waveguide. Numerical simulations predict that operation frequencies of about 3 MHz are possible. The measurements have also allowed the determination of the previously unknown thermo-optical coefficient of undoped amorphous silicon at this wavelength.

Structural and electrical properties of highly conductive μc-Si(P) layers

Abstract Thin films of phosphorus doped μc-Si have been prepared in a glow discharge reactor starting from hydrogen diluted silane using less than 5 watt RF power. Conductivities as high as 41 S/cm have been measured on samples deposited at 210°C. The discharge parameters and reactor geometry will be examined in order to correlate the really dissipated RF power to the structural and electrical properties of the material. XRD, SEM, Raman spectroscopy and electrical characterization techniques have been used. All the samples show clusters that increase with the film thickness, while at the same time the crystallite size changes in the range 30–75 A.

Amorphous Silicon Based Waveguides And Light Modulators For Silicon Low-Cost Photonic Integrated Circuits

This paper reports about the fabrication and experimental test of an interferometric light intensity modulator integrated in a low loss (0.7 dB/cm), amorphous silicon based waveguide. It measures approximately 1 mm in length, while its cross section is 30-μm-wide and 3-μm-high. The device, which exploits the strong thermo-optic effect in thin film a-Si for its operation, is designed for application at the infrared wavelengths of 1.3 and 1.55 μm. The measured maximum operating on-off switching frequency of the device is 600 kHz. The very simple fabrication technology involves maximum process temperatures of 230 °C, and is therefore compatible with the standard microelectronic technology. This offers a new opportunity for the integration of optical and electronic functions on the same substrate.

Correlation Between Minority Carrier Diffusion Length and Microstructure in a-Si:H Thin Films

Aim of this work is to investigate the opto-electronic properties of amorphous hydrogenated silicon (a-Si:H). The deposition temperature nas been used as a driving force to modify the morphology and bonded hydrogen distribution. The influence of the hydrogen microstructure on the carriers μτ product has been examined. The majority and minority carrier μτ have been evaluated from the diffusion length measurement, by using the Steady State Photocarrier Grating (SSPG) technique, and from the photoconductivity in the steady state condition (SSPC). The μτ values have been correlated with the defect density and the Fermi level position. Some considerations are proposed to explain the carrier transport in terms of the compositional inhomogeneities in Si:H alloys due to the morphological variations.