Quasiballistic transport in GaAs-based heterojunction and homojunction bipolar transistors

An iterative approach to solving an implicit integral relation for the electron distribution function in the base of a bipolar transistor is exploited to achieve a solution to the field-free Boltzmann transport equation. The method, which is based on one previously applied to Si homojunction transistors, is extended here to hetero- and homojunction transistors in the GaAs material system. This involves incorporating tunneling and reflection into the boundary condition for the injected flux at the emitter end of the quasineutral base, and considering anisotropic and inelastic scattering mechanisms. The ballistic, scattered, and reflected portions of the distribution are examined as the base width is reduced to values where quasiballistic transport is evident. Numerical results are presented for the carrier concentration and velocity profiles, and for the base transit time. (C) 1998 American Institute of Physics. [S0021-8979(98)07821-9].