Modeling of SiGe-base heterojunction bipolar transistor with gaussian doping distribution

Modeling of the inverse base width modulation effect in HBT transistor with graded SiGe base

“…In further considerations material parameters are defined as follows. Intrinsic carrier concentration in the SiGe base is given as [4]:…”

“…where: n i0Si -intrinsic carrier concentration in pure silicon, ∆E GEFF -the effective band gap narrowing in the base due to the presence of Ge (∆E GGe ) and due to heavy doping effects (∆E GAPP ). It is assumed that band gap depends linearly on y Ge (7.5 meV per 1% of Ge, e.g., [4]). The model of Klaassen-Slotboom-de Graaff [5] was chosen to describe ∆E GAPP .…”

“…The model of Klaassen-Slotboom-de Graaff [5] was chosen to describe ∆E GAPP . The ratio of the effective density of states in a SiGe base to that in a silicon one is defined in the following way as a function of Ge content (for y Ge ≥ 0.01) [4]:…”

“…As expected, the increase of Ge gradient lowers m, i.e., collector current becomes much more dependent on V BE . The importance of including the dependence of D nSiGe on F and that of γ(x) on y Ge (x) in J C model of SiGebased HBT has been demonstrated in [4]. The influence of these two effects on the collector current pre-exponential ideality factor m is discussed below.…”