Cut-off frequency of a drift transistor

Abstract: A method is described that selects, for each transistor in a circuit, the model of least complexity that will give acceptable accuracy. The capability to assess model adequacy derives from a self-consistency test in which the values of currents and voltages computed in a simulation of the circuit behavior are compared with onset parameters, to determine whether these computed values are consistent with the approximations underlying the device models used in the simulation. The onset parameters for a model are the terminal currents and voltages above or below which the model fails to give a satisfactory representation of device behavior. The authors set forth the onset parameters for the Ebers-Moll model and discuss their determination by terminal measurement and by calculation based on the transistor makeup. The paper limits consideration to the static behavior of transistors operating in the forward-active mode.

Abstract: Various expressions for the emitter-collector transit time of a heterojunction bipolar transistor (HBT) can be found in the literature. It is not obvious whether the product of the emitter contact resistance and the base-emitter capacitance should be included in the emitter-collector transit time expression. This paper theoretically demonstrates that the above product does not appear in the transit time expression. Additional physical insights observed from the derived transit time expression and comparison to a similar expression for homojunction bipolar transistors will be discussed.

Abstract: The effect of mobility degradation at high impurity concentrations on the cut-off frequency of a diffused base transistor with exponential impurity profile in the base has been considered analytically. It has been shown that the cut-off frequency exhibits a maximum with increase in emitter and concentration. The results are compared with those of complementary error function and Gaussian base impurity profiles.

Abstract: Preparation of lattice matched InP/InGaAs(P) heterojunctions was first reported by Antypas et all in 1972. Initially research efforts were mainly concentrated on optical devices. In recent years three-terminal InP/InGaAs(P) heterojunction bipolar transistors (HBT's), for microwave and digital applications, have gained more interest. Several laboratories have reported HBT's fabricated by LPE techniques but these were not optimised. More recently devices grown by MBE and CBE have been demonstrated in the InP/ InGaAs system. This paper is concerned with discussing the intrinsic advantages to be gained by fabricating HBT's in this material system and progress attained to date is reviewed.

Abstract: Certain conventionally defined characteristic frequencies of a drift transistor are related to each other, to the basic transistor parameters, and to minority carrier time constants, using the theory of the simple one-dimensional model The Frequencies are the common emitter and common base cut-off frequencies, and the frequency at which the magnitude of the common emitter short circuit current gain is unity; the minority carrier time constants are the effective lifetime, the average transit time, and the average time of stay in the base Several approximations for the frequency variation of the current gains are given, and used to find how junction capacitances and base resistance affect the measurement of the characteristic frequencies Finally the maximum frequency of oscillation is discussed, and the high-frequency figure of merit redefined in a way compatible with the conventional definition