A study of the DC and RF degradation of Be-doped AlGaAs/GaAs HBTs under constant current stress

AlGaAs/GaAs HBTs play an increasingly important role in the market of wireless products. Although it is still a matter of scientific debate whether Be or C is the optimum base dopant, the technology of Be-doping is more mature, and commercially more important than that of C-doping. However, it is well known that the outdiffusion of Be toward the emitter (a degradation mechanism that is accelerated by high current densities) produces a displacement of the p-n base-emitter junction which results in an increase of its turn-on voltage (V_BEon) and a reduction of the current gain β. Less treated are the effects of Be diffusion on the device RF characteristics, and their correlation with the DC degradation mode. Moreover, the stress time and current dependences of the degradation are not conclusively documented