STATIC AND DYNAMIC BEHAVIOR OF A SI/SI0.8GE0.2/SI HETEROJUNCTION BIPOLAR-TRANSISTOR USING MONTE-CARLO SIMULATION

A theoretical study of a Si/Si1-xGex/Si heterojunction bipolar transistor using Monte Carlo simulations is reported. The geometry and composition of the emitter-base junction are optimized using one-dimensional simulations with a view to improving electron transport in the base. It is proposed to introduce a thin Si-P spacer layer, between the Si-N emitter and the SiGe-P base, which allows launching hot electrons into the base despite the lack of natural conduction-band discontinuity between Si and strain SiGe. The high-frequency behavior of the complete transistor is then studied using 2D modeling. A method of microwave analysis using small signal Monte Carlo simulations that consists of expanding the terminal currents in Fourier series is presented. A cutoff frequency f(T) of 68 GHz has been extracted. Finally, the occurrence of a parasitic electron barrier at the collector-base junction is responsible for the f(T) fall-off at high collector current density. This parasitic barrier is lowered through the influence of the collector potential.