A self-consistent DC-AC two dimensional electrothermal model for GaAlAs/GaAs microwave power HBTs

A 2D self-consistent model has been developed to investigate the coupled electrothermal problem in GaAlAs/GaAs HBTs under DC and AC conditions. Electrical and thermal aspects of device behavior are simultaneously investigated by means of a nodal analysis of the distributed and physics-based model using a circuit simulator. The effects of base widening and the temperature dependence of the thermal conductivity are taken into account. Rigorous simulations are compared to the results given under different approximations. In particular, the sensitivity to the temperature dependence of the electron mobility is used to highlight the beneficial role of the negative temperature coefficient of the current gain in determining the thermal stability of the device. An HF performance criterion (maximum stable gain) is calculated and then compared to the results derived from the isothermal approximation