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The widely used vertical bipolar inter-company (VBIC) model for bipolar junction transistor-heterjunction bipolar transistors (HBTs) was modified to incorporate high-current effects. The modified VBIC model keeps all features of the original model and adds new features such as mobile carrier modulation of the base-collector capacitance, high-current Kirk effects, high-current reverse emitter-base injection, and current dependence of the reverse transit time in HBTs. The new model accurately fits the dc I-V characteristics, the bias-dependent transit-time, and S-parameters at active and quasi-saturation region biases. It is shown that the new formulation accurately models the strong current dependence of [f.sub.t] and [G.sub.max] over a wide range of biases. It also predicts very well the power performance in class-AB operation and at the loading for maximum power-added efficiency and maximum output power. The model also shows good fitting of two-tone linearity characteristics when simulated with the same fundamental and harmonic load conditions as in the measurements. Index Terms--Heterojunction bipolar transistor (HBT), high current, semiconductor device modeling, vertical bipolar inter-company (VBIC).

Optimum loading for a power enhancement-mode pseudomorphic high electron-mobility transistor (E-pHEMT) is determined by a systematic harmonic load-pull simulation. The simulation uses a modified Angelov-Parker model that can accurately predict dc, small-signal RF, and power performance of the devices. The optimum second harmonic loading for a 2-mm device is found to be open circuit and the optimum third harmonic is at the third quadrant, which is about 1 [angle] 210[degrees]. The measured versus modeled results show very good agreement and, therefore, verify the model. The simulation predicts that as high as 80% poweradded efficiency can be achieved for E-pHEMT under optimum source and load termination with harmonic tuning.

Using novel characterization techniques, output gain, and phase jumps (with respect to input frequency or input level) of multistage monolithic-microwave integrated-circuit power amplifiers were correlated with heterojunction field-effect transistor (HFET) drain-current kinks and negative gate resistances. Both physical and phenomenological models were used to explain the correlation through hole-trapping and self-biasing mechanisms. A remedy involving bias-stabilization diodes was experimentally verified. Other possible remedies are also discussed. The present conclusion can be extended to other metal-semiconductor field-effect transistor and HFET amplifiers with similar gain/phase jump problems. Index Terms - Charge - carrier processes, electric breakdown, gain control, heterojunction, MESFET's, microwave power amplifiers, MMIC's, phase control.

A comprehensive large-signal model of a GaAs MESFET is presented to account for charge conservation and effects of dispersion and self-heating. An improved set of capacitance and charge equations, along with an enhanced Triquint Own model (TOM)-like drain current model, is used for consistent small- and large-signal simulations. Charge conservation is satisfied by deriving the capacitance part of the model from charge equations. Transconductance and output conductance dispersion is modeled by combination of a feedback network and a subcircuit, which describes the self-heating effect. An improved description of the near-pinchoff characteristics, high-voltage breakdown, and gain compression at high-current region in the TOM is introduced. The new model accurately predicts the I-V, CV, bias-dependent S-parameter, waveform, power, and linearity characteristics of the MESFET.

A large-signal heterojunction bipolar transistor (HBT) model has been developed which includes self-heating, collector transit-time, and RF-breakdown effects. The model has a compact form which is based on a compromise between accuracy and utility. As such, the model can be readily extracted and verified with the aid of RF waveform measurements. Using the model in simulations, it was found that RF breakdown was dependent on base biasing and loading conditions. Therefore, with proper circuit design, the maximum output power of the HBT can significantly exceed the limit of open-base breakdown voltage.