Base transit time minimization with fixed base dopant dose

The problem of determining the doping profile minimizing base transit time TB in a BJT is investigated for the case in which the net active dopant dose Q in the quasi-neutral base is held fixed, but the width W of the base is allowed to vary. It is found that the minimum TB is obtained, for reasonable values of Q, by shrinking the base width until the profile becomes box-shaped with doping equal to the solid solubility. This occurs at so narrow a base width, however, that in any practical device it will always be favourable to grade the base doping profile

Simple model for front and end contact resistances

The paper proposes a simple model for contact resistance in the Berger and Kelvin structures which approximately accounts for finite substrate thickness in terms of closed-form expressions. The present model agrees with the transmission-line model for large contact resistivity, but deviates significantly in the other extreme

Bounds on bipolar transistor base transit time

The paper provides upper and lower bounds on the base transit time of a bipolar transistor which hold regardless of the shape of the base doping profile. These bounds apply, for the case of conventional bipolar transistors, when both the diffusion coefficient of the mobile carriers and the effective bandgap narrowing depend on doping density. They would also apply to composition grading in heterojunction bipolar transistors

A method for contact resistivity measurement using thick, uniformly doped substrates

A method for measuring contact resistivity ρ{variant}c which makes use of thick, uniformly doped semiconductor samples is presented. The contacts take the form of parallel stripes which extend across the width of the sample, producing a two-dimensional current distribution. Conformal mapping is used to relate the resistance measured between the stripes to ρ{va

Distribution of base dopant for transit time minimization in a bipolar transistor

A means to determine the doping profile minimizing base transit time in a bipolar transistor is presented, assuming that the width of (he neutral base is held constant. It is found that the optimum profile is not close to the exponential decrease from emitter to collector predicted by earlier studies