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Strained Si/Ge Superlattice for Optical Modulation at 1.3 Mm

IP.com Disclosure Number: IPCOM000100223D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Iyer, SS: AUTHOR [+2]

Abstract

Disclosed is a method for modulating light at 1.3 mm in an optical waveguide by forming part of the waveguide in the conducting channel of an FET. Switching of the FET causes variable absorption modulation within the waveguide.

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Strained Si/Ge Superlattice for Optical Modulation at 1.3 Mm

       Disclosed is a method for modulating light at 1.3 mm in
an optical waveguide by forming part of the waveguide in the
conducting channel of an FET.  Switching of the FET causes variable
absorption modulation within the waveguide.

      The bandgap of Si can be engineered by the application of
strain in a strained Si/Ge superlattice configuration (1). In this
invention the composition of the superlattice is chosen such that in
quiescent condition absorption of light at 1.3 mm occurs.  The
waveguide structure is shown in Fig. 1.  The superlattice structure
forms part of the section of a silicon waveguide, and the modulation
of the absorption in the superlattice can be effected by its
incorporation as the conducting channel of an FET (see Fig. 2).

      In Fig. 3, the the band diagrams for the modulator when the
device is in flat band condition (solid) and when inverted (dashed)
are shown.  Clearly in the former condition, 1.3 mm transitions are
allowed, while in the latter case the relative position of the Fermi
level with respect to the conduction band edge in the narrow gap
Si-Ge layer causes the transitions to be bleached since a large
number of conduction band states are filled with electrons. Excitonic
absorption is also quenched.  The bleaching effect will be reduced
somewhat due to bandgap renormalization and the influence of the
Stark effect on available states. Thus, varying the ap...