Abstract

The large absorption depth for red-infrared photons propagating in silicon makes fast response times for integrated photodetectors difficult to achieve. Typical high speed photodetectors for light in this wavelength range are PIN diodes, where the intrinsic layer is used to extend the region of electric field to allow drift mechanisms to dominate diffusion mechanisms in carrier transport across a junction boundary. Since the fabrication of a large intrinsic layer is not easily incorporated in VLSI processing, an alternative approach has been developed in which the direction of light propagation in the silicon is altered by a surface-relief grating at the silicon-silicon dioxide interface. Propagation of light at an oblique angle in the silicon allows the photons to be absorbed closer to the silicon surface, within the drift region of a shallow vertical pn junction. We expect this grating structure to be made using periodic structures drawn in standard fabrication masks and the bird's beak effect that disturbs the flatness of the silicon-silicon dioxide interface during oxide growth. We present a description of layout modifications required to generate the periodic mask structures and computer simulations of diffraction efficiency for various grating modes with varying grating depth and period.

© 1989 Optical Society of America