  Surface plasmon polaritons (SPPs) give an opportunity to break the
diffraction limit and design nanoscale optical components, however their
practical implementation is hindered by high ohmic losses in a metal. Here, we
propose a novel approach for efficient SPP amplification under electrical
pumping in a deep-subwavelength metal-insulator-semiconductor waveguiding
geometry and numerically demonstrate full compensation for the SPP propagation
losses in the infrared at an exceptionally low pump current density of 0.8
kA/cm$^2$. This value is an order of magnitude lower than in the previous
studies owing to the thin insulator layer between a metal and a semiconductor,
which allows injection of minority carriers and blocks majority carriers
reducing the leakage current to nearly zero. The presented results provide
insight into lossless SPP guiding and development of future high dense
nanophotonic and optoelectronic circuits.
