The University of British Columbia

McKelvey's one-flux method, which has recently been used to investigate transport in short-base bipolar transistors and to specify the carrier mobility in a forward-biased barrier, is put into perspective by a comparison with the usual continuity and drift-diffusion equations. For a bulk semiconductor region in which a small electric field is present, and under typical operating conditions, it is shown that the use of the time-dependent flux method is equivalent to solving the usual continuity and drift-diffusion equations under low-level injection. It is then shown that recent one-flux analyses of short-base transport, for both d.c. and a.c. conditions, are equivalent to solving the continuity and drift-diffusion equations with appropriate boundary conditions. It is pointed out that the use of the flux method to resolve the long-standing issue of specifying the carrier mobility within a forward-biased barrier is impeded by a lack of knowledge of the required backscattering coefficients. Recent suggestions for these backscattering coefficients are carefully examined; the physical basis for the choices made, and hence the resulting values of mobility and diffusivity, are questioned.