R. De Rosa

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.

Spectroscopic ellipsometry study of interfaces and crystallization behavior during annealing of a-Si:H films

Spectroscopic ellipsometry is used to investigate the subsurface reactions related to hydrogen diffusion during the annealing process at temperatures ranging from 250°C to 650°C of very thin a-Si:H films in stacked structures. A gradual and partial crystallization of the a-Si film develops from both the substrate and the top surface layers depending on annealing time. The SE approach is also applied to the characterization and optimization of the annealing process of ITO/a-Si:H/c-Si heterostructures for solar cells application. The effects of the annealing process on the a-Si:H microstructural modification and on the optical properties of the indium tin oxide (ITO) layer are deduced.

Innovative Diodes based on Amorphous-Porous Silicon Heterojunction

In this paper the authors present an innovative diode based on the heterojunction between amorphous silicon and porous silicon grown on crystalline silicon. The device architecture gives several advantages. Deposition of amorphous silicon on porous material realizes high performance junction at temperature less than 250 C and it passives the porous layer against the natural oxidation due to aging in the environment. Porous technology allows to obtain a controlled textured silicon surface independently from crystalline silicon orientation just to give the opportunity to reduce surface reflectivity and the blue shift of the absorption spectra in solar cell application. Solar cells were characterized by I-V dark/light and quantum yield measurements. Under standard AM 1.5 light they obtained photovoltaic conversion efficiency greater than 10%. Change in photoluminescence in different gas environments showed for gas sensor applications give rise to encouraging results. In dark condition they found the typical diode behavior.

Amorphous–Porous Silicon Heterojunction for Gas Sensor Application

In this work we studied the compatibility of amorphous thin film technology with the porous silicon in case of large area applications like gas sensors. We found that thin amorphous silicon layer growth on porous silicon substrates preserves the room temperature photoluminescence of porous material. Also amorphous–porous silicon heterojunction shows a good rectifying behaviour. Those properties, correlated with the porous silicon sensitivity to the gas environments, can be effectively used to realise heterojunction diodes whose current voltage characteristics are modified by the gas reactivity on the porous surface. Sensitivity of those devices and response time to different gas exposure have been investigated.

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.