Electro-optical modulating multistack device based on the CMOS-compatible technology of amorphous silicon

Sandro Rao,Francesco G Della Corte

doi:10.2971/jeos.2010.10040s

Abstract

In this paper we report results on a field-effect induced light modulation at λ = 1.55 µm in a high-index-contrast waveguide based on a multisilicon-on-insulator (MSOI) platform. The device is realized with the hydrogenated amorphous silicon (α-Si:H) technology and it is suitable for monolithic integration in a CMOS Integrated Circuit. The device exploits the free carrier optical absorption electrically induced in the semiconductor core waveguide. The dynamic behaviour of the device was experimentally and theoretically analyzed in presence of a visible illumination showing a link between the photogeneration and the free carriers provided by doped α-Si:H layers. The core waveguide contains several thin dielectric films of amorphous silicon carbonitride (α-SiCN) embedded along its thickness highly enhancing the absorbing action of the modulator held in the on-state.

Highlights

The optoelectronic properties of hydrogenated amorphous silicon, α-Si:H, and related materials have been exploited for decades almost exclusively for the fabrication of lowcost large-area photovoltaic devices
Of the waveguide and the modulated light emerging from the chip was collected and collimated by an objective and detected by an InGaAs photodiode
The average effective absorption coefficient variation ∆αeff induced in the core waveguide is 0.35 cm−1, 0.65 cm−1 and 0.75 cm−1 respectively at 10 V, 20 V and 30 V biases, corresponding to an electric field of 0.13 MV/cm, 0.26 MV/cm and 0.39 MV/cm across the 40 nm thin insulating α-SiCN layers

Summary

Introduction

The optoelectronic properties of hydrogenated amorphous silicon, α-Si:H, and related materials have been exploited for decades almost exclusively for the fabrication of lowcost large-area photovoltaic devices. Thanks to their unique characteristics of transparency at the infrared wavelengths [1], refractive index tunability and good technological compatibility with all microelectronic process [2], many α-Si:H-based photonic devices, such as LEDs [3], photodetectors [4] and lightwave guiding [2], have been fabricated successfully. A λ = 1.55 μm radiation propagating in a planar waveguide has been modulated in amplitude by a visible wide spectrum light sources [5] In such cases the interaction of amorphous silicon with an infrared radiation strictly depends on the density of localized states available in the pseudogap and their respective occupancy state. This is a peculiarity of amorphous semiconductors which makes a substantial difference in the optoelectronic applications with respect to the homologous crystalline counterparts

Methods

Results

Conclusion