  We propose a plasmonic modulator with semiconductor gain material for
optoelectronic integrated circuits. We analyze properties of a finite-thickness
metal-semiconductor-metal (F-MSM) waveguide to be utilized as an ultra-compact
and fast plasmonic modulator. The InP-based semiconductor core allows
electrical control of signal propagation. By pumping the core we can vary the
gain level and thus the transmittance of the whole system. The study of the
device was made using both analytical approaches for planar two-dimensional
case as well as numerical simulations for finite-width waveguides. We analyze
the eigenmodes of the F-MSM waveguide, propagation constant, confinement
factor, Purcell factor, absorption coefficient, and extinction ratio of the
structure. We show that using thin metal layers instead of thick ones we can
obtain higher extinction ratio of the device.
